Government regulators may have greatly overestimated the cancer risk from asbestos, according to new research that suggests the billions of dollars spent to clean up contaminated public buildings may have been a massive case of overkill.
Exposure to moderate levels of the asbestos does not appear to significantly increase a person's risk of developing lung cancer, the authors of the new study conclude after analyzing health records for thousands of women from a Quebec district that has the world's greatest concentration of asbestos mines and mills.
"We found no measurable excess risk of death due to lung cancer," Montreal epidemiologist Michel Camus and two colleagues wrote in a report published in today's New England Journal of Medicine. "The [Environmental Protection Agency] model overestimated the risk of asbestos-induced lung cancer by at least a factor of 10."
But other scientists disagreed sharply with the report's conclusions and cautioned against any weakening of government protections.
"All forms of asbestos are carcinogenic," said Philip J. Landrigan, a professor at New York's Mount Sinai School of Medicine who serves as an adviser to the EPA on children's health issues.
Asbestos, a fibrous, heat-resistant material commonly used for insulation or fire-proofing, is well known to cause cancer among workers exposed to heavy concentrations of the mineral. Since the 1980s, fears about possible cancer risks have driven public officials to investigate potential threats to school children and others who use buildings that contain asbestos.
But far less is known about the effects of lower doses. For years, U.S. policy on asbestos has been driven by EPA mathematical models that extrapolate from earlier cancer studies involving miners and industrial workers. More recently, though, scientists have questioned whether EPA's models can reliably gauge the cancer risk from far lower levels of airborne asbestos found in some older buildings.
To test the EPA's model, the three Canadian scientists tracked the cancer rate among thousands of women who lived in a cluster of towns in Quebec's asbestos district. Most of the women lived less than three miles from an asbestos factory or mine at a time before modern pollution controls were in use. In the 1940s and 1950s, the air around the mills was so dense with asbestos fibers "you could literally see it," said co-author Jack Siemiatycki, a professor of epidemiology with the University of Quebec's Institut Armand-Frappier.
"Housewives would have to sweep the dust off the balconies on a regular basis. You could see who had gone to church on Sunday mornings by the footprints on the sidewalks," Siemiatycki said.
By simply breathing, people in the study area would have been exposed to asbestos levels that are five times higher than the maximum exposure limit for today's asbestos workers, Siemiatycki said. Yet the region's women turned out to be no more likely to develop lung cancer than comparable groups of women in other parts of the province.
"If these people didn't experience excess rates of cancer, it's hard to understand the meaning of all the risk projections being done for schools and buildings where people are panicking because they're being exposed to small amounts," Siemiatycki said.
A separate component of the study will examine whether the Quebec women experienced higher rates of mesothelioma, a rarer form of cancer that attacks the lung's outer lining and is nearly always linked to asbestos. Preliminary data points to a small increase in the cancer rate near the asbestos mills.
"The mesothelioma story remains open," Siemiatycki said. "We may find some excess risk, but if we do it won't be a large problem in terms of public health."
Scientists who criticized the study found fault not with the researchers' data but with their interpretation. Landrigan, the Mount Sinai professor, said it was "quite a leap" to suggest that government standards for asbestos in buildings should be revamped.
Landrigan contends that the Canadian team's analysis is misleading because asbestos exposures are not all equal. Near the Quebec mines, most of the asbestos dust would consist of larger particles that can be easily expelled from the lungs. But the particles found in older buildings are smaller and potentially more damaging.
"They really compared apples and oranges," he said.
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