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Supporters of fluoridation assert that lots of things are toxic (salt, iron, Vitamin A, none of which we add to our water), and that the quantities of fluoride consumed through drinking water are inconsequential. The flaw in their reasoning is that the difference between "optimal" fluoridation levels and a potentially toxic dose is small. The amount of fluoride different people ingest varies considerably. It is inevitable that some people will end up crossing the line between safe and toxic exposure because of fluoride's high inherent toxicity.

One subset of the population we should be especially concerned about is infants and young children. According to the Environmental Working Group, infants and young children are at a three to four times higher risk of over-exposure to fluoride than adults because of their smaller size.

What are the risks? One of the biggest involves the effect of fluoride on the brain. A 1998 study by Varner, Jensen et al, reported brain-damaging effects in rats given fluoride in drinking water at the same level deemed "optimal" by pro-fluoridation groups (one part per million). Studies from China show decreases of between 5 and 10 IQ points in children who get more fluoride than control groups.

Another risk is bone pathology, because fluoride bio-accumulates in the bones. A study published earlier this year found adolescent boys who drank moderately fluoridated water had a five times greater risk of developing osteosarcoma, a rare form of bone cancer. Numerous studies have found a higher rate of hip fractures in fluoridated versus nonfluoridated communities.

Fluoride inhibits enzyme systems and can impair both the kidneys and the thyroid gland. The recently released National Research Council report reviewed virtually all published research on fluoride and concluded in a number of key areas relating to human health that "more research is needed." The most charitable interpretation you can put on the existing science is that there are significant unanswered questions about fluoride's safety, even at low levels of exposure.

These unanswered questions are made more urgent by a growing body of evidence showing that fluoridating water does not reduce tooth decay. Historically, tooth decay has declined at comparable rates in both fluoridated and nonfluoridated areas. The largest U.S. study on fluoridation, conducted by the U.S. Public Health Service, found the decay rate of permanent teeth was virtually the same in fluoridated and nonfluoridated areas.

Fluoride proponents are fond of quoting statistics suggesting that fluoride dramatically reduces tooth decay in specific age groups. These statistics are bogus. They do not control for the fact that fluoride delays tooth eruption by from one to two years. When proponents assert that at age 9, children from a fluoridated area have 50 percent less decay, they forget to mention that they also have 50 percent fewer teeth. When these statistics are adjusted for delayed tooth eruption, the apparent advantage for fluoridation disappears.

Maybe there was a time when fluoridation seemed like a good idea. There was a time when bleeding people with leeches to treat a fever seemed like a good idea, too. It's time to put an end to this bizarre custom of disposing of toxic waste by dumping it in our drinking water. Fluoridation is an idea whose time has come - and gone.

• David Ottoson owns Rainbow Foods in Juneau.