HOGANSBURG – On Monday morning, F. Henry Lickers amazed and even brought to tears his audience of scientists and activists in a longhouse of the Mohawk people.

For three hours, the director of the Department of Environment for the Mohawk Council of Akwesasne described a dark chapter in his people’s history that began in the fluoride-filled smokestacks of nearby aluminum factories.

“Fluoride didn’t just kill the cows on Cornwall Island,” Mr. Lickers said. “Its effects were compound. It was strong enough to corrode individual Mohawk relationships. It was strong enough to divide a nation.”

In the last leg of a three-day conference on the dangers of fluoride, Mr. Lickers was invited to speak to 40 scientists, journalists and activists in the field. At St. Lawrence University, Canton, the group had listened to lectures on the effects of fluoridated water and toothpaste on the brain and bones. They even held a raffle for nonfluoridated toothpaste from India.

Mr. Lickers’s presentation at the St. Regis Mohawk Reservation emphasized how prolonged exposure to fluoride, whether airborne or in the water and land, can devastate a community.

It was a presentation, though, that neither the Centers for Disease Control and Prevention nor the American Dental Association attended.

“It is very important to appreciate the difference between industrial exposure to high levels of fluoride and the one part per million level of fluoride that occurs naturally in many water systems and which can be adjusted in others, safely and effectively.” said William R. Maas, director of the division of oral health at the CDC. “I think most people do understand the difference, but they can be susceptible to misunderstanding arising from distortion and alarming rhetoric given by some crusaders.”

Mr. Lickers began his lecture with the arrival 9,000 years ago of the Haudensaunee (Iroquois) people to the area. He described the community as deeply agricultural, with a strong cattle, fishing and trapping heritage.

Pushing forward to the late 1950s and the arrival of the Reynolds Metals plant in Massena, he said, that all changed.

The company’s aluminum manufacturing generated fluoride gas as a byproduct, hurting animals, insects and even people, he said.

By the 1960s, Mohawk farmers reported that honeybees and grasshoppers had disappeared from the area, while sick cattle were found downwind from the Reynolds plant.

Evidence also had been collected in 1978 by scientists such as Bertram Carnow of the University of Illinois School of Public Health that the community had a range of health problems often associated with fluoride. These included abnormalities in nervous and skeletal systems and lungs. No conclusive evidence, however, could link fluoride to the Mohawk ailments.

Even without this evidence, Mr. Lickers said, the weakening of cow bones and their eventual deaths from fluoride disrupted the community’s harmony. Cattle farmers no longer bartered with fishermen or trappers. And when toxins from the factories started to kill fish and other animals, these other trades stopped as well.

The fiber of the Mohawk agricultural base came apart, and in that void came the nontraditional economies of gambling and smuggling and the civil war of 1990. It was a war over the future direction of the community and it cost millions of dollars for the United States and Canada and the lives of both Mohawk and non-Mohawks, Mr. Lickers said.

A settlement was eventually reached in 1980 with Alcoa Inc. and Reynolds on the fluoride issue. The Mohawks received $464,000 in 1980 from the aluminum producer after agreeing not to sue the company for 10 years for damage to cattle and vegetation.

While the settlement was not completely satisfactory, Mohawks now have more of a voice in the company’s cleanup projects throughout the area, he said.

After hearing Mr. Lickers’s narrative, Lorna Rosenstein of Utah cried as she reflected on the plight of the Mohawk people.

“When you see something like fluoride that is seemingly harmless have such an impact on a community as it did for the Mohawks, you can’t help but think it profound,” said Ms. Rosenstein, an activist with a grass-roots coalition concerned with the quality of her state’s water supplies. “It is lucky for this community that they had the will to fight and get their concerns known to industry and the government.”

For Michael P. Connett, project director of the Fluoride Action Network, which organized the conference, the Mohawk experience with fluoride represents a problem for all citizens and not just for those living near fluoride-emitting factories. It’s a problem for anyone who regularly ingests fluoridated water or uses fluoridated toothpaste, allowing the chemical to build up in their system, he said.

“Studies have already shown that problems associated with aluminum workers are manifesting in communities that simply drink fluoridated water,” he said. “Fluoride accumulation is a threat and the government should make every effort to stop it.”