A recent article in our local paper caught my eye; it reported that the U.S. Department of Health and Human Services was recommending lowering the amount of fluoride in drinking water. The reason is that many of us are getting additional fluoride from other dental products (toothpaste, mouthwash), and too much fluoride is not a good thing.

Fluoridation of drinking water has been official U.S. Public Health Service policy since 1951, as a way to prevent tooth decay. As of 2006, about 70% of the U.S. population that receives its drinking water from a public supply was drinking fluoridated water, about 180 million people. The recommended level is between 0.5 and 1.0 mg/L (ppm).

Despite its obvious health benefits, fluoridation has always been controversial. Fluoride always makes me think back to the great movie “Dr. Strangelove,” and the crazy General Jack Ripper, who thought that the addition of fluoride to drinking water was sapping our “precious bodily fluids.” That was satire, but plenty of people have opposed fluoridation on various grounds. The U.S. EPA has set a drinking water standard of 4 mg/L (the World Health Organization recommends a lower level, 1.5 mg/L), because of mottling of teeth and potential bone disease known as fluorosis, where fluorine replaces the hydroxyl ion in bone hydroxyapatite. It’s not a pretty picture.

There are places in the world with naturally high fluoride in groundwater, often in igneous terrains and arid climates. The dominant major ions in high fluoride waters are sodium and bicarbonate, the water being naturally soft. Here’s a link to a good summary report on worldwide occurrences of high fluoride.

Illinois doesn’t have igneous rock aquifers and most groundwater in the state is typically moderately to very hard (high levels of calcium and magnesium), but there are some areas with naturally elevated fluoride, although typically not extremely high levels. Here’s a plot showing fluoride vs. sodium for samples from the Water Survey water quality database in Kane, Kendall, and Will Counties:

Most samples are < 2 mg/L, but there are about 25 with fluoride > 2 mg/L. And most of these are from relatively shallow wells (< 500 ft):

We haven’t systematically looked at the data yet, but it appears that some of these wells are near the Fox River and fault zones in the region, which suggests there may be water migrating up from depth. As the water passes through shale beds, they make be picking up fluoride (and sodium).