The ability of water to dissolve and redistribute substances to widespread areas can cause adverse health effects to exposed populations. Dichotomies exist between positive and negative health impacts from various minerals or elements; fluoride is one such element. Fluoride exposure provides a viable example for the famous toxicology quote, “the dose makes the poison.” Populations are generally exposed to fluoride in drinking water, where it is either natural or manually added, it is a mineral that has the ability to help or hinder exposed populations.
Man with sketal fluorosis in Turkana, Kenya. Photo: protectorsystems.com
Once absorbed, fluoride is rapidly circulated throughout the body. Fluoride is distributed between the plasma and blood cells, with plasma levels being twice as high as blood cell levels and the half life ranging between 3 to 10 hours. Approximately 99% of fluoride in the human body localizes to bones and teeth; fluoride is incorporated by replacing the hydroxyl ion in hydroxyapatite to form fluorohydroxyapatite. Fluoridation additives used in treating drinking water may include hexafluorosilicic acid (H 2 SiF 6), sodium fluoride (NaF), and sodium hexafluorosilicic acid (Na 2 SiF 6). According to the World Health Organization, total daily fluoride exposure in a temperate climate should be approximately 0.6 mg/l per adult per day in an area with no current fluoride additives or treatment in drinking-water resources.
The benefits of fluoride exist primarily in tooth enamel development in children. While higher than suggested fluoride levels by the World Health Organization, it has been determined that permissible levels (approximately 0.8 mg/l) reduce tooth decay and aid in the retention of calcium to strengthen teeth and bones. Fluoride use in caries prevention efforts have resulted in significant reduction of dental caries in substantial populations.
"Overexposure to fluoride has been associated with many adverse health effects."
Alternatively, overexposure to fluoride (greater than approximately 1 mg/l) has been associated with many adverse health effects. The most visible physical defect is enamel fluorosis; the condition is visible through the discernible brown stains and markings on teeth occurs when enamel covering of teeth fail to crystallize properly. A study by the National Research Council, 2006, concluded that severe enamel fluorosis occurs in 10% of children exposed to fluoride concentrations of 4 mg/l. Additional health effects have been reported in various studies and include neurodevelopmental delays in children, dental fluorosis, clinical stage II skeletal fluorosis, and skeletal factures in both children and adults. Prolonged exposure to high levels of fluoride can create severe bone abnormalities which present in crippling deformities.
Choi et al., 2012 report the inverse association between high fluoride exposure and children’s intelligence. As low as 1 mg/l fluoride exposure were determined to be positively linked to lower IQ levels in children. It was recently determined that fluoride may be a developmental neurotoxicant, affecting brain development at exposures much lower than toxic levels in adults. Obviously, cognitive impairment in children has a myriad of negative developmental outcomes associated with it.
A fluoride free water kiosk. Photo: theguardian.com
According to the World Health Organization ‘Fluoride in drinking-water’ written under the Water Quality, Guidelines, Standards, and Health, 2001, the most significant sources of fluoride exposure is located in the East African Rift through Kenya. These naturally-created veins of fluoride are associated with historical volcanic activity. In Kenya, the Soda Lake fluoride levels of Lake Elmentaita and Nakuru have concentrations up to 1,640 mg/l and 2,800 mg/l respectively. A survey completed by Nair in 1982 tested groundwater samples throughout Nairobi, the Rift Valley, and Central Province in Kenya. Fluoride levels were high in these regions, with maximum concentrations reaching between 30 to 50 mg/l. On average, over half of tested sites within these areas reached fluoride levels from 1.1 to 8.1 mg/l. These areas are physically marked by severe dental fluorosis throughout the population. Additional research needs to investigate neurotoxic effects; it is highly likely that children and adults are being significantly affected.
Fluoride contamination in Kenya needs to be addressed. Several defluoridation techniques exist today. Defluoridation processes must first be developed into centralized or de-centralized systems. Once the type of system has been evaluated and determined, defluoridation techniques may then be considered.
A child with dental fluorosis in Njeri, Kenya. Photo: wsup.com
Defluoridation of water usually occurs through either flocculation or adsorption. Flocculation employs hydrate aluminum salts that bind with fluoride ions in water. Due to alkalinity, lyme or bleaching powder can be added to disinfect the water. This technique can be carried out in large or small containers and can be used as a point of use system per household use. Coagulation and settling of the flocculation procedure takes approximately two hours. Adsorption filters water through a column that is packed with adsorbent (e.g. activated alumina or charcoal or ion exchange resins) that becomes saturated with fluoride ions, allowing clean water to pass through. This method is also suitable for household to use, but must promote caution in the disposal process to avoid recontamination of nearby groundwater. Lastly, calcium and phosphate compounds or contact precipitation chemicals can be added to the upstream water supply; though, this technique is not necessarily sustainable and may be costly.
Populations throughout Kenya are overexposed to fluoride in the drinking water; this overexposure causes adverse health effects, including dental and skeletal fluorosis and impaired brain development. Ultimately, economical and sustainable defluoridation techniques need to be adequately adapted to the at-risk population and be easily accessible to members of the community. These technical solutions may also need to be paired with educational programs that consider aspects of fluoride contamination and re-contamination, rain-water harvesting techniques, access to health-based information within healthcare clinics. It is important to address the root of the problem, but also provide information on harmful health effects of over-exposure to fluoride, while continuing to understand, monitor, and evaluate fluoride levels in the drinking water supply throughout Kenya.