VARIABILITY IN FLUORIDE CONTENT OF SUBSURFACE WATER RESERVOIRS

Groundwater may contain high concentrations of fluoride. In most count ries, however, information on the fluoride content is scarce and anecd otal. The aim of the present study was to make a comprehensive assessm ent of F- in the groundwater of a representative area of Norway, there by establishing a more solid basis for appropriate health counseling. Relevant technical information was collected, together with water samp les from 1063 underground water sources in 31 municipalities in the co unty of Hordaland. One thousand and two water samples were analyzed fo r F- and pH with an F--selective electrode and a pH electrode, respect ively. Mean F- was 0.30 mg/l (range, <0.02-9.48). Fourteen per cent of the wells contained water with F- levels greater than or equal to 0.5 0 mg/l. In three municipalities well water had a mean F- concentration >0.70 mg/l; in one instance the mean was as high as 1.45 mg/l. In 10 municipalities maximum F- values were >1.50 mg/l. F- values showed a p ositive correlation with the pH of the water and the depth of the well s (P < 0.01) and a negative correlation with the age of the well (P < 0.05). The results indicated that low-capacity wells deliver water wit h a higher F- value than high-capacity wells. This trend, however, was not statistically significant. The results show that high-F groundwat er is prevalent and emphasize that information on domestic water suppl y must be available before supplementary fluoride is prescribed for ca ries prophylactic purposes.