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Something nasty in the water?

March 24, 2006 By Emma Marris This article courtesy of Nature News.

Fluoride leaching from rocks is turning kids' teeth brown.

The maximum allowable limit of fluoride in US drinking water is too high, according to a report from the National Academies' research unit this week.

The Environmental Protection Agency (EPA) currently enforces a limit of 4 milligrams of fluoride per litre of water, and advises a lower limit of 2 mg/l for children younger than nine years for aesthetic reasons.

But the Academy report says that these rules don't seem to be good enough. Children are drinking water in areas where fluoride is at about 4 mg/l, and some 10% of them have an ugly condition known as severe enamel fluorosis, where teeth are mottled brown and pitted. Most on the panel agreed that this affliction, which is found around the world, goes beyond the aesthetic and can be considered an "adverse health effect".

The 450-page report also noted that there are some conflicting data on whether or not high levels of fluoride can be correlated with bone cancers.

The EPA, which commissioned the Academy study, says it will now get down to the business of re-evaluating its maximum limit. At the moment, says report co-author Charles Poole, an epidemiologist at the University of North Carolina at Chapel Hill, the United States's maximum limits are higher than that of many other countries.

Not about fluoridation

The report only looked into high levels of fluoride, well above the 0.7-1.2 mg/l amount that is intentionally added to water in some communities to help prevent cavities. This practice, known as fluoridation, has long been a subject of controversy. The higher limits of 2-4 mg/l are usually only reached in areas where fluoride naturally leaks out from surrounding rocks into the water or where it is an industrial pollutant.

"We thought about calling our report 'Not About Fluoridation' and stamping NAF as a little acronym on every page," jokes Poole.

Some vocal groups claim the risk to teeth and bones outweigh the benefits of fluoridation. This is contrasted by the majority of scientific opinion, says John Stamm, a dentist and epidemiologist at the University of North Carolina. "Fluoridation is overwhelmingly supported by the dental profession and public health agencies," he says.

Clear cut

The results in the report show that there seems to be a very clear cut-off point where fluoride no longer causes ill effects. Below 2 mg/l, severe enamel fluorosis is only seen very rarely. "We are dealing with levels that look like they are not very far apart, but they are very different in terms of health effects," says Stamm.

Such a clear line between harmless and harmful is unusual, notes Poole. "In 30 years of environmental epidemiology, I have never seen a curve that so clearly showed a threshold," he says.

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