RESEARCH TRIANGLE PARK, N.C., April 26 – A panel of scientific experts today endorsed the findings of a Federal investigation showing that a compound widely used to fluoridate public water supplies may cause bone cancer in male rats.

The panel found that the evidence inconclusively demonstrated a weak association between fluoride consumption and the bone cancer in male rats.

Federally sponsored scientists who conducted the study say the finding does not in itself imply a hazard to humans from drinking fluoridated water. But opponents of fluoridation who attended the meeting today argued that the evidence was now strong enough that fluoridation should be halted. Roughly half of all Americans drink fluoridated water. A representative of the American Dental Association attending the meeting condemned the report of the fluoride study as misleading. Another proponent of fluoridation threatened the scientists with legal action if they retained the wording of their report.

A 2-Year Study

The public meeting conducted by 13 independent scientists here today set the official seal on results of a two-year investigation by the National Toxicology Program, a branch of the Public Health Service. Mice and rats of both sexes were fed varying amounts of sodium fluoride at doses up to 20 times those human beings might encounter in drinking water. The animals were killed and very carefully examined.

The most striking result was that some male rats in the study contracted osteosarcoma, or bone cancer, significantly more often when they received increasingly high levels of sodium fluoride. But neither female rats nor any of the mice showed any increase in bone cancer.

The National Toxicology Board therefore said, ”The current findings are inconclusive, but are weakly supportive of an association between sodium fluoride administration and the occurrence of osteosarcomas in male rats.”

This was unanimously adopted by the panel of independent scientific experts convened to give the report ”peer review.” Several panelists urged that in view of the evidence, a more comprehensive investigation should be begun.

Dr. John R. Bucher, the National Toxicology Program scientist who directed the study, said his agency could perform a more comprehensive investigation. ”But we have no mandate or plans to do so at present,” he said.

Dr. Michael A. Gallo, an environmental scientist who acted as chairman of the meeting today, reminded participants that its purpose was not to decide on the possible carcinogenicity of fluorides to humans, or on the advisability of fluoridating water.

Undertone of Tension

”At this level,” he told a reporter, ”scientists are simply trying to assess possible hazards. Other scientists would then examine possible human exposure to that hazard to determine risk. Finally, risk must be weighed against potential benefit.”

But despite the cautious tone of most of the speakers at the meeting, there was an undertone of tension that occasionally found voice. ”

We’re all very much aware that the chemical we’re considering here is no ordinary one, but is the substance in nearly everyone’s drinking water,” said Dr. Ellen K. Silbergeld of the University of Maryland Medical School. ”But as scientists we must discuss sodium fluoride with no more emotion than we would when considering the toxicity of any other chemical.”

Among the public witnesses permitted to speak was Dr. John A. Yiamouyiannis of Delaware, Ohio, a scientist who is a leading opponent of water fluoridation. ”The evidence brought to light in the National Toxicology Program report coupled with earlier studies is clear,” he said. ”Sodium fluoride should now be declared a Class A carcinogen.” Class A is the designation for dangerous substances.

A study conducted 13 years by Dr. Yiamouyannis and Dr. Dean Burk, former head of the cellular chemistry section of the National Cancer Institute, concluded that 10,000 excess cancer deaths occur each year in the United States because of water fluoridation. The Yiamouyannis-Burk investigation caused so much public concern that Congress ordered the investigation that resulted in the report ratified today.

Conclusions Are Assailed

Several other speakers appearing as witnesses before the panel of scientists took strong exception to the report. Speaking for the American Dental Association, Dr. John W. Stamm declared that the conclusions of the National Toxicology Program were not justified, since animal studies were not reliable indicators of effects on humans.

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