Water Fluoridation—A Sound Public Health Practice

natural presence of more than 1.5 ppm. of fluorine in the waters used by those so affected, resulted in the analysis of many natural waters to determine their fluoride ion content. The presence of fluorides in natural waters is associated with igneous rocks and with prior volcanic action, or with sedimentary rocks which have been influenced by the weathering of igneous rocks. Fluorides are therefore most likely to be present in ground waters mineralized by sandstone and limestone formations. The fluorides in rocks are largely insoluble, so the concentration of soluble fluorides present in natural waters almost never exceeds 15.0 ppm. and is usually less than 1.0 ppm. Naturally occurring soluble fluorides are similar in chemical composition to the fluoride compounds being added to public water supplies in fluoridation treatment. A study of the distribution of fluoride-bearing waters by Hill, Jelinek and Blayney ( 1 ) discloses that natural waters in the 32 states investigated usually contained low concentrations of fluorides, but that many natural waters mostly located in Ohio, Indiana, Illinois, South Dakota and Texas contained concentrations of fluoride ion greater than 1.0 ppm. The survey d scloses that approximately 3,000,000 people are served by water supplies c ntaining from 1.0 ppm. fluoride ion to more than 5.0 ppm. as shown in Table 1.