More than 600 scientists and health experts are urging Congress to halt the addition of fluoride to public drinking water until the controversial treatment is proven safe.

In a strong statement Thursday, the health professionals called upon lawmakers to stop fluoridation in communities across the nation until their safety concerns are reviewed at congressional hearings. The group, the Fluoride Action Network, cited fresh scientific evidence that fluoridation, long promoted to fight tooth decay, is ineffective and carries serious health risks

No hearings on fluoridation are currently planned before any Senate or House committee.

Among the petitioners is Arvid Carlsson, 84, a Swedish scientist best known for his work with the neurotransmitter dopamine and its effects in Parkinson’s disease and a co-recipient the 2000 Nobel Prize for Medicine. “Fluoridation is against all principles of modern pharmacology,” he said. “It’s really obsolete.”

The anti-fluoride signers are challenging the powerful American Dental Association, which is well-entrenched on Capitol Hill and calls fluoridation one of the best public health ideas ever.

Dr. Sally Cram, an ADA spokeswoman, told Roberta Baskin, an investigative reporter for WJLA-TV, “Absolutely, fluoride is safe, it’s effective, it has reduced the decay rate in the population by about 20 to 40 percent over the last 60 years.” Baskin’s report aired on the Washington ABC-TV affiliate Thursday.

Baskin also interviewed Bob Carton, a former toxic substance scientist at the Environmental Protection Agency, who told her that adding fluoride to water was a mistake from the beginning. “It was a foolish thing to do years ago,” Carton said. “They didn’t have enough information. It hadn’t really been tested.”

Baskin cited a recent study by the National Academy of Sciences that concluded toxic levels of fluoride can lead to severe, permanent pitting of the enamel in children’s teeth and that fluoride can also build up in the bones to cause pain, stiff joints and skeletal abnormalities when they get older. She reported, however, that “the Environmental Protection Agency isn’t about to make any quick decisions about the academy’s finding that toxic levels of fluoride must be drastically lowered.”

Baskin’s WJLA report also featured an interview with Benjamin Grumbles, an EPA water quality specialist, who told her, “We take [the academy’s] recommendations very seriously. We also have a commitment to get additional information and validate it and work with other public health authorities.”

Supporters of fluoridation cite research by the U.S. Centers for Disease Control and Prevention that shows fluoridation of drinking correlates to reductions in tooth decay on the order of 15 percent to 40 percent in municipalities across the United States.

Excessive amounts of the chemical, however, can lead not only to irreversible tooth discoloration, a condition called “fluorosis,” but also to other health issues, including an increased risk of bone breakage, particularly among the elderly.

The problem, according to the Fluoride Action Network, is that the very water that is treated for dental purposes is also used in the preparation of many food products — from baby formula and cereal to juices, sodas, wines, beers and even fresh produce. These scientists hold that since most toothpastes also contain added fluoride, many people are ingesting far more fluoride than they should.

Water fluoridation by public authorities has often provoked controversy. Advocates say that it is similar to fortifying salt with iodine, milk with vitamin D and orange juice with vitamin C and claim it is an effective method of preventing tooth decay.

The Fluoride Action Network and other opponents, however, contend that fluoridation can have harmful health effects such as bone cancer and osteoporosis. Another issue is the potential discoloration of children’s second teeth once the baby teeth are gone. Besides being embarrassing, there is no cure. Several studies have also shown how low-to-moderate doses of fluoride can lead to eczema, reduced thyroid activity, hyperactivity, IQ deficits and premature puberty.

Some opponents also claim that releasing fluoride compounds into municipal water supplies takes away individual choice as to the substances a person ingests and amounts to forced mass medication.

On the other side, concerns have risen that our increased reliance on nonfluoridated bottled water instead of fluoride-treated tap water, especially among teenagers, may be leading to increases in tooth decay.

The Food and Drug Administration has long required warning labels to keep toothpaste out of the reach of children under 6 years old. “If more than used for brushing is accidentally swallowed, get medical help or contact a Poison Control Center right away,” the mandatory labels say.

In 2005, Baskin reported, some 22,000 Americans did so.

“Too much of any good thing can be a bad thing,” the ADA’s Cram told Baskin in their on-air interview. However, Cram added, “we prevent a lot of suffering and pain that is totally unnecessary and preventable, both in adults and children.”