Is fluoridated water good for you? Or is it a poison that causes young boys to die of bone cancer?

For 60 years, U.S. cities and towns have been adding fluoride to tap water, and for 60 years pro-fluoride advocates have been unable to forge a scientific consensus in favor of the practice.

Those who say fluoridation is harmful are often portrayed as crackpots scanning the heavens for UFOs.

Yet the opponents of fluoridation include a winner of the Nobel prize in medicine, one of Canada’s top dental researchers and 11 unions that represent 7,000 environmental and public health professionals at the U.S. Environmental Protection Agency.

“We have this good science showing this elevated risk of fatal bone cancer, and nothing’s happening in the regulatory community. It’s unconscionable,” said William Hirzy, a union vice president who is a senior scientist in pollution prevention and toxics at the EPA.

While Massachusetts lawmakers consider a proposal to mandate water fluoridation throughout the state, the EPA unions recently called on their agency to classify fluoride as a carcinogen. They also urged Congress to declare a moratorium on water fluoridation programs.

Research has tied fluoridated water to bone cancer in young boys, hip fractures in women and increased levels of lead in drinking water. But the biggest challenge for anti-fluoride lobbyists may be winning the public relations battle.

“The might of the government is very hard to overcome,” Hirzy said. “You know how difficult it is for the federal government to admit they made a mistake….How long did it take for the public health service to get off endorsing lead as a great thing in gasoline?”

The EPA declined an interview request to respond to the union demands, saying the agency is awaiting the results of a new federal review of fluoride research expected in February.

The toxic question

More than one-third of Massachusetts cities and towns have fluoridated drinking water, including all of those served by the Massachusetts Water Resources Authority.

No one disputes that fluoride, at high enough levels, is toxic. The chemical has been used as rat poison, and fluoridated toothpastes must include a warning telling people to call a poison control center if they swallow more than used for brushing.

But can tiny amounts of fluoride mixed with drinking water prevent cavities without causing terrible diseases? This is the question that has been hotly debated for the past 60 years.

Most European countries have decided that fluoridating water is too risky. Dr. Arvid Carlsson, a Swedish pharmacologist who won the 2000 Nobel prize for research involving the nervous system, argues that some people are sensitive to the chemical’s negative effects even when exposed at low levels.

“The addition of fluoride to water supplies violates modern pharmacological principles,” Carlsson wrote in the postscript to journalist Christopher Bryson’s recent book, “The Fluoride Deception.”

“Recent research has revealed a sometimes enormous individual variation in the response to drugs….This measure is ethically questionable and unnecessarily expensive.”

Studies that tie fluoridated water to bone cancer and other diseases are dismissed by U.S. government officials and dental associations, who argue that most researchers have not found risks associated with fluoride.

“The predominant view of the scientific community is that there is an optimal range of…fluoride, below which you don’t have the protective effects against tooth decay and above which you get the detrimental effects,” said Howard Pollick, an American Dental Association spokesman and dentistry professor at the University of California, San Francisco.

Holes in evidence?

But even fluoride’s intended benefits are up for debate. The government’s official position is that fluoride improves dental health, and the U.S. Centers for Disease Control and Prevention has called fluoridating drinking water one of 10 great public health achievements of the 20th century.

But does it even work? John Bucher, one of the federal government’s top toxicology officials, doesn’t think so.

“I don’t have any real reason to believe it’s dangerous. I don’t have any real reason to believe it’s effective, either,” said Bucher, deputy director of the environmental toxicology program at the U.S. National Institute of Environmental Health Sciences (NIEHS).

Bucher said fluoride is more effective at preventing cavities when applied topically, like in toothpaste.

The American Dental Association, a strong supporter of adding fluoride to public water supplies, says recent studies show the practice lowers tooth decay rates by 20 percent to 40 percent.

But even the ADA acknowledges that fluoride’s effects on teeth are not all positive. Nearly one in three children suffer from dental fluorosis, a usually mild condition that causes discoloration of the teeth and can create pits on the surface.

“If you were to introduce water fluoridation now, it would cause more damage to teeth than what it is supposed to prevent,” said Hardy Limeback, a professor at the University of Toronto and former head of the Canadian Association for Dental Research.

Limeback was a supporter of fluoridated water before causing a stir in 1999 when he decided that fluoride causes more harm than good.

“I wasn’t aware of all the toxicology literature. As soon as I read it, I changed my mind,” Limeback said. “It’s contaminated even when you dilute the crude material down to one part per million (the amount recommended in drinking water). It still has enough arsenic to increase the risk for cancer.”

Cancer concerns

Pro-fluoride advocates say the cancer risk is overblown, pointing to the government’s National Research Council 1993 review of fluoride studies which found that the legal fluoride limit of four parts per million in water is appropriate.

“More than 50 epidemiological studies have examined the relation between fluoride concentrations in drinking water and human cancer,” the NRC wrote. “These studies provide no credible evidence for an association between fluoride in drinking water and the risk of cancer….If there is any increase in cancer risk due to exposure to fluoride, it is likely to be small.”

This federal report was written three years after the U.S. Public Health Service found a small increase in osteosarcoma, a type of bone cancer, in male rats ingesting sodium fluoride. Bucher, who conducted the study, said the finding was “equivocal,” meaning it is suggestive of a cancer link but not conclusive.

More evidence connecting fluoride to cancer was found in 2001, by Harvard student Elise Bassin, who earned a doctorate in medical sciences for a thesis that found boys in communities with fluoridated water have a significantly increased risk of developing bone cancer.

Bassin’s thesis took center stage in the fluoride debate when her supervisor, professor Chester Douglass, wrote that Bassin’s work supports his view that fluoridated water poses no risk even though she found just the opposite.

Harvard is now investigating an ethics complaint filed against the professor by the nonprofit Environmental Working Group, and Bassin’s thesis is being reviewed by the National Research Council as it analyzes new fluoride research to update its findings issued in 1993. The updated report, requested by the EPA, is expected in February.

Bones and poison

There is more than just cancer to worry about when it comes to fluoride, some researchers have found. Women have a higher risk of hip fractures when they drink water with fluoride, according to a 1999 study published in the American Journal of Epidemiology.

The most commonly used type of fluoride may also increase the public’s exposure to lead. Natick chemist Myron Coplan, in research conducted with Roger Masters of Dartmouth College, found that young children in communities that use a class of fluoride chemicals known as silicofluorides are about twice as likely to have elevated levels of lead in their blood.

The finding is supported by new research from the Environmental Quality Institute at the University of North Carolina-Asheville, which ran fluoridated water through pipes made partially of lead for six weeks to determine if certain combinations cause extra lead to escape the pipes.

The institute found that silicofluorides, combined with chloramines — a common disinfectant containing chlorine and ammonia — causes a lead level in water at least twice as high as that in non-fluoridated water, said institute co-director Richard Maas.

In response to the work of Masters and Coplan, the U.S. government published an analysis this year that found an increased lead risk in fluoridated communities of up to 70 percent, but the study’s lead author said the difference was not considered statistically significant because of the sample size. But he also said the report does not disprove the lead allegations.

“That’s not to say that if a new study were conducted there might be some association. We certainly encourage other studies,” said lead author Mark Macek of the University of Maryland.

Silicofluorides, which include the chemicals hydrofluorosilicic acid and sodium silicofluoride, are hazardous waste products recovered from the phosphate fertilizer industry.

Twenty-five years ago, Coplan said, he worked for a Florida fertilizer company designing equipment to separate silicofluorides from plants producing phosphate fertilizer.

“I stood right next to this enormous pond where this toxic poisonous waste was being collected and eventually shipped off,” Coplan said.

Coplan later argued against fluoridation in Natick, but the town began using the chemical despite unanimous opposition from an expert panel formed by town officials in 1997.

Silicofluorides have never been tested on animals to determine their toxicity, Bucher and other government officials acknowledge, but in large enough quantities they are clearly dangerous.

In February, several blocks of downtown Phoenix, Ariz., were closed for 12 hours after a chemical company spilled nearly 300 gallons of hydrofluorosilicic acid. State environmental officials fined the company and warned the public that the fluoride substance is “harmful by ingestion, inhalation, or skin contact.”

Mass. plans

Despite research linking low levels of fluoride in water to health problems, there are no plans locally to stop using the chemical. The Massachusetts Water Resources Authority has fluoridated water since the 1970s, and will continue to do so as long as the CDC supports fluoridation, said planning director Stephen Estes-Smargiassi.

“We’re not in the business of health research,” Estes-Smargiassi said. “If the CDC changes its mind, you can be assured the MWRA (will, too).”

William Maas, director of oral health at the CDC, said the preponderance of evidence proves fluoridated water reduces tooth decay and doesn’t cause harm, and he expects the National Research Council to reach the same conclusion in its February report.

“There’s no question in my mind that fluoride is good for us,” he said.

The question of whether to add fluoride to water is usually handled on a town-by-town basis. Many have decided the risks are too great. But 30 lawmakers in Massachusetts want to take the choice away from communities by mandating fluoridation of all water supplies serving at least 5,000 people.

Sen. Pamela Resor, D-Acton, proposed the fluoridation mandate after listening to a presentation from a group of public health and dental professionals, she said.

When Resor filed the legislation, she was not even aware of the research connecting fluoridated water with bone cancer, increased lead intake and hip fractures. She didn’t learn of these studies until being contacted by a reporter.

“I will certainly look into all of these,” Resor said. “I certainly don’t want to do something that has any of that kind of detrimental impacts.”