Fluoride is considered an essential ion for strengthening bones and preventing tooth decay especially in children. For this reason, it is often added to toothpaste and other foods to enhance protection against dental decay. Also, in some countries, synthetic substances such as fluorosilic acids, sodium fluorosilicate and sodium fluoride are added to drinking water supplies to increase the fluoride level. Controversies still exists as to whether the addition of these substances to drinking water supplies is a viable option or not.
Although consumption of fluoride is noted to have some health benefits for human health, excessive intake of the ion largely through groundwater sources leads to dental fluorosis (tooth decay) and in severe cases, results in skeletal fluorosis (bowed or Curved legs).
Dental fluorosis is a disease in which fluoride together with other environmental conditions attacks the teeth and forms an irreversible rust-like deposit on it thus consequently destroying (chipping, fracturing or breaking) the enamel, dentine and the cementum of the teeth. This imposes a lot of stigma on the affected persons. It affects the way they mingle and interact with others. For example, in the Bongo District of Ghana (where the groundwater is predominantly contaminated with fluoride), it is reported that the discoloration of the teeth of school going children as a result of fluorosis, reduces their confidence level and those who cannot stand the ridicule drop out of school.
If the levels of fluoride intake are very high and the period of exposure spans over years, the unhealthy impacts of the ion on the teeth also begin to appear on major bones of the human body and this is termed as skeletal fluorosis (bowing or curving of the legs).
Although there is limited information on other equally intriguing health implications of high fluoride consumption such as stomach troubles etc, a study conducted in India in 1993 by Sushecla and others on “the prevalence of endemic fluorosis with gastrointestinal manifestations of people in some villages in India” revealed that loss of appetite, nausea, abdominal pain, flatulence, constipation and intermittent diarrhoea are the early signs of fluoride toxicity.
How much fluoride is good for drinking water
The World Health Organisation (WHO) has made it one of its primary goal that “all people, whatever their stage of development and their social and economic conditions, have the right to have access to an adequate supply of safe drinking water” for which it has taken upon itself the responsibility ‘to propose ….regulations, and make recommendations with respect to international health matters …. ’. Thus, the WHO water quality target for drinking water for fluoride is 1.5mg/L. This value is the maximum allowable limit of the ion in drinking water considered to pose minimal health impacts on humans. The minimum requirement is 0.5 mg/L (Dental cavities may occur especially in children). The optimal range is 0.5-1.5 mg/L where generally no adverse effects occur. However, above 1.5 mg/L, there are risks of dental fluorosis and much larger values may lead to skeletal fluorosis.
The chemistry of fluorosis
Human bones are made of hydroxylapatite. This hydroxylapatite and fluoroapatite (remember fluoride comes from fluoroapatite) are both end members in the apatite group and thus the hydroxyl (OH-) ion in the hydroxylapatite of human bones is easily displaced by the fluoride ion (F-) in the apatite structure, consequently increasing the brittleness and solubility of the bone structure. Over an extended period, this then manifests as bowed or curved legs as the body begins to put on weight and more load exerted on the legs.