By Kim Murphy

Proponents of fluoridating Portland's water supply had no trouble getting the local Urban League on board. Here in the biggest city in the country that still doesn't treat its water to prevent tooth decay, studies show that low-income children and kids of color have been hit hardest by untreated cavities.

"Do we really want our children to be suffering from something we could prevent? Why would we not want to be involved?" said Jerome Brooks, an Urban League advocacy contractor who has helped marshal the civil rights group behind a fluoridation measure on Tuesday's municipal ballot.

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But at the National Association for the Advancement of Colored People, the city's other major advocacy group for blacks, leaders were worried about lacing the water with a mineral that might aggravate diabetes-related kidney problems, whose incidence rate is higher in the black community. "People of color are disproportionately going to suffer by adding what I call a toxin to the water," said Clifford Walker, a board member at the NAACP's Portland chapter.

That the city's two premier black organizations are at loggerheads over the fluoridation referendum is only one measure of how the fluoride debate has turned this city's traditional liberal politics on its head.

Cities across America have been fighting fluoride wars since the 1940s. Dentists and public health advocates armed with fluoride's strong track record of strengthening teeth have been challenged by anti-government fringe groups warning against bureaucrats trying to medicate the water supply.

Today, most major American cities, and more than 66 percent of the population, have fluoridated water flowing through their taps.

But not Portland, which voted against fluoridation three times between 1956 and 1980. When the City Council exercised its own power to pass a measure last year, critics amassed 20,000 signatures in 22 days, and a referendum was put on the ballot.

The measure has divided the city's powerful progressive community. Mainstream liberals see fluoridation's benefits as obvious, but they have hit an unexpected juggernaut of opposition from people who usually are their allies _ among them rock musicians, Green Party activists and organic farmers, who have been carrying signs warning of an impending "Zombie Nation."

The Sierra Club warns that fluoridation could put traces of arsenic, lead and other heavy metals in the Columbia and Willamette rivers, jeopardizing not only threatened populations of salmon but human health as well.

A former chief of the American Cancer Society in Oregon, Rick North, has joined the opposition, saying he believed fluoridation was a good idea until he learned it had been linked at some dosages to cancer, thyroid disease, diabetes and other ailments. "I started studying the science, and I was amazed, and very concerned," he said.

Traditional doctors, dentists, business groups, and minority health groups have joined forces behind Healthy Kids, Healthy Portland's fluoride campaign. Opponents at Clean Water Portland have signed on chiropractors, nutritional therapists, acupuncturists and food co-ops -- plus a few dentists.

In a city known to observe political sensitivities, the fluoride feud has turned ugly. Yard signs have been stolen and burned, or covered with dog poop.

Evyn Mitchell, who's managing the pro-fluoride campaign, said she has seen online bullying, heckling at public forums "and a lot of things that are really very un-Portland."

"We've heard reports of it dividing families and friends," she said. "It's been hard to see the progressives in Portland so deeply divided."

At the same time, the issue engages Portlanders in the same way as debate over climate change, salmon restoration or logging policy.

Proponents say Oregon ranks 48th among states in access to fluoridated water and has one of the poorest records of child dental health, with 35 percent of the state's children suffering from untreated tooth decay as of 2007. Neighboring Washington, where cities such as Seattle are fluoridating the water, has only half as many.

Mitchell likes to tell people that the Centers for Disease Control and Prevention calls water fluoridation "one of 10 great public health achievements of the 20th century," and that the American Medical Association and the American Dental Association have strongly endorsed it.

But critics say that it's impossible to know how much fluoride people are exposed to -- it depends on how much they drink -- and that harmful effects have been found at high dosages. "If you go to the CDC website, 43 percent of their (fluoride) samples have arsenic, 2 percent have lead," said Kellie Barnes, a physical therapist who is the spokeswoman for Clean Water Portland.

(c)2013 Los Angeles Times