FLUORIDE BIOACCUMULATION AND ENAMEL FLUOROSIS FROM CHRONIC EXPOSURE THROUGH DRINKING WATER

Chronic exposure to excessive amounts of fluoride (F^─) during tooth development causes dental fluorosis (DF) that lead to enamel demineralization and excessive enamel loss in severe cases. This study considers how F^─ concentration in urine and fingernails predict the severity of enamel disorder in rural communities of the Main Ethiopian Rift (MER). The study examined the DF status of 316 individuals (10 to 50 years old) in 22 communities with groundwater F^─ concentrations that ranged between 0.55 to 12 mg/L. A total of 301 and 287 individuals provided 12-hour urine and fingernail samples, respectively. The mean F^─ concentrations in groundwater were 5.2±3.1 mg/L (range: 0.55–12 mg/L), while those in urine were 9.8±7.5 mg/L (range: 0.44–34 mg/L). More than 96% of urine samples contained F⁻ concentrations at a level higher than the Biological Exposure Index (BEI) value of 2 mg/L. The fingernail F^─ content ranged from 0.65 to 30 mg/Kg (mean: 5.2±4.4 mg/Kg). There was a strong and significant positive correlation between F^─ in drinking water and 12-hour urinary F^─ excretion (r=0.74, p<0.001, n=287), fingernail F^─ content (r=0.6, p<0.001, n=258), and mean individual measures of DF severity using the Thylstrup-Fejerskov (TF) index (r=0.42, p<0.001, n=316). Among all teeth that were examined, 63% had TF-scores 1 or higher (mild to severe), with the proportion of mild, moderate, and severe TF scores being 23%, 18%, and 22%, respectively. Younger individuals (10 to 35 years old) had a much greater proportion (81%) of teeth showing signs of DF than older individuals (36 to 50 years old; 27.5% of teeth). The lower DF severity observed in the older individuals suggests that such individuals faced lower exposures in early childhood, which is the most critical period of risk to DF. The exceptionally high F^─ bioaccumulation in individuals in this region suggests the need for further research on other potential health consequences of high F^─ exposures, including skeletal and neurodevelopmental disorders, which could add to major public health challenges already facing this low-income region.