TOE NAILS AS A BIOMARKER OF CHRONIC FLUORIDE EXPOSURE SECONDARY TO HIGH WATER FLUORIDE CONTENT IN AREAS WITH ENDEMIC FLUOROSIS.

There is a need to monitor the body burden of fluoride (F) in endemic areas without resorting to bone biopsy. For a biomarker of F exposure to be applicable in a large population, it should be easily collectible without objections from the donors and be an effective, a reliable, and a valid method of F estimation. The present study was designed as a population based observational cross-sectional study. The F content in toe nail clippings was determined by the dry ashing method in a total of 40 local residents residing in three F endemic areas of the Jaipur district of Rajasthan, India, with mean drinking water F levels of 4.1, 4.8, and 5.6 ppm. The F levels of serum and 24 hr urine were also estimated in the same population. The mean nail ash F levels were extremely high with a range of 82.38±6.89 - 103.92±16.89 ppm. Highly significant relationships were present between the water F levels and the F levels in toe nail (p<0.001), serum (p<0.001), and urine (p<0.001). Similarly, significant relationships were present between the toe nail F levels and the F levels in serum (p<0.001 and p<0.01) and urine (p<0.001 and p<0.01). The presence of F in toe nail indicates that F is obtained from the systemic circulation to the nail beds and deposited in the nails by either continuous incorporation or secondary concentration. Toe nail F is a useful biomarker for both subchronic and chronic F exposure. [ABSTRACT FROM AUTHOR]