Big toenail and hair samples as biomarkers for fluoride exposure – a pilot study

Abstract

Background Biomarkers can aid in detecting and preventing clinical disease through the recognition of change in biological samples. The objective of this case-control study was to further the knowledge on the use of big toenail and hair samples as biomarkers for fluoride exposure. Methods A total of 48 participants from an endemic (IC) and a non-endemic (SC) fluorosis region were included. Big toenail and hair samples were collected from each participant and the fluoride concentration was determined. The results of 42 participants were reported: 21 participants (11 males and 10 females, mean age 15.66 + 2.61 years) from IC and 21 participants (11 males and 10 females, mean age 15.06 + 0.79 years) from SC. Results The mean fluoride concentration of big toenail (2.34 ± 0.26 mg/kg) and hair (0.24 ± 0.04 mg/kg) in the endemic region was significantly higher than the mean fluoride concentration of big toenail (0.98 ± 0.08 mg/kg) and hair (0.14 ± 0.02 mg/kg) in the non-endemic region ( p < 0.001 and p = 0.004, respectively). The Receiver Operating Characteristic (ROC) analysis showed that the Area Under the Curve (AUC) value was 0.889 for big toenail (p < 0.001) and 0.762 for hair (p = 0.004) samples. The fluoride assay for big toenails exhibits greater observed accuracy than does the fluoride assay for hair. Conclusion Nail and hair samples can serve as biomarkers to detect biological fluoride exposure according to the data of this pilot study. Nevertheless, hair is less sensitive and specific as a biomarker when AUC values of big toenail and hair samples were compared.

Dental Fluorosis according to Birth Cohort and Fluoride Markers in an Endemic Region of Colombia

“…Nails are a noninvasive, readily available biomarker of chronic, subchronic, and acute F exposure. e F concentration found in the toenails confirms its value in measuring a community's chronic F [23,25]. e exposure time reflects the increase in the DF incidence in the birth cohorts and coincides with the F concentration found in the study population's toenails.…”

“…The F concentration found in the studied cases' toenails coincides with that found in similar studies, i.e., toenail samples, age group, and the number of subjects, conducted in other geographic areas [ 20 ]. Elekdag-Turk et al [ 25 ] found a mean F concentration of 2.34 ± 0.26 mg/kg in endemic regions and a mean of 0.98 ± 0.08 mg/kg in nonendemic regions. Buzalaf et al [ 20 ] and Amaral et al [ 28 ] reported F concentrations of 1.49–2.80 mg/kg and 2.15 (0.39)–2.64 (0.41) μ g F/g, respectively.…”

“…Although some studies have reported higher F concentrations in fingernails than in toenails, it is currently recommended to use toenail samples, especially from the first toe, because it is fast growing and provides enough sample for the analysis. Some reports have shown that toenails are less exposed to external contamination than fingernails [ 7 , 20 , 25 , 28 ]. However, this can vary depending on the lifestyle of the rural populations.…”

Recent Biomarkers for Monitoring the Systemic Fluoride Levels in Exposed Populations: A Systematic Review

“…Nails and hair can be highlighted for their capability of reflecting the short-term and long-term exposure to fluorides (from months to years), non-invasive access, and long storage periods without degradation or loss of properties, and because both are supplied by blood during the growth stage, these present the average concentration of plasma fluoride levels from chronic intake [ 23 , 25 , 26 , 27 ]. Furthermore, both nails and hair as keratinized matrices share histological features that make them able to attach different types of elements, which is useful for the toxicological evaluation in several research areas [ 28 ].…”

“…In both biomarkers, higher F − levels were found in the endemic fluorosis area, showing significant differences ( p < 0.001 for nails; p = 0.004 for hair). Although it was established that nails and hair were adequate biomarkers for monitoring the exposure to fluorides, toenails had more sensitivity for this purpose [ 25 ].…”