By Wade Rawlins
Asbestos is among the most thoroughly investigated of any workplace health hazard. Yet, certain questions still intrigue researchers including the relative potencies of different types of asbestos, the role of fiber size in determining toxicity and the workplace hazards of unregulated mineral fibers that mimic asbestos. But should these questions be a barrier to a national ban on asbestos use?
Researchers at the University of Washington, the U.S. Public Health Service and the Center for Construction Research and Training, argue in the current issue of the American Journal of Industrial Medicine, that unanswered questions about asbestos should not stand in the way of more protective occupational health policy.
Along those lines, the researchers say the most important health priority regarding the six forms of asbestos regulated by federal workplace safety authorities is—simply put— to ban their production and use. Policy makers often must act in the face of uncertainties to safeguard public health, they say
“There is ample reason to do this without waiting for more evidence on the relative potency of chrysotile versus the five regulated amphibole asbestos minerals,” Dr. Michael A. Silverstein, a professor of environmental and occupational health sciences at the University of Washington, and his co-authors write.
After all the World Health Organization’s International Agency for Research on Cancer recently reaffirmed its conclusion that all forms of asbestos including chrysotile cause mesothelioma as well as cancers of the lung, larynx and ovary. The World Health Organization has urged a worldwide ban on asbestos. Forty-three countries now have asbestos bans in place.
Waiting for more precise information about potential risks before taking action is essentially making a date with an uncertain future and exposing more workers to asbestos-related disease. The diseases typically don’t appear until decades after exposure.
The researchers note that attempts since the 1970s to develop dependable statistical risk assessment models for asbestos have been repeatedly undercut by limitations on reliable exposure data. The conditions of exposure vary too much and remain difficult to classify.
EPA’s current risk assessment method assumes that all types of asbestos fibers are equally potent for causing lung cancer and mesothelioma. But lobbyists for the asbestos industry have sought to change the model to back their claim that chrysotile asbestos—the most common in use today—is less toxic.
In 2008, EPA’s attempt to develop a risk assessment model predicting the relative toxicities for different combinations of asbestos fiber types and dimensions eventually ran aground. EPA’s scientific advisory board recommended that the model be rejected, and EPA administrator agreed that it couldn’t be used as the basis for setting public policy. At the time, Silverstein and more than 80 fellow scientists submitted comments opposing the change, saying there had been no new studies that offered a compelling reason for a new risk assessment.
“The history of asbestos cancer risk assessment illustrates the point that elegant mathematics do not make good public policy,” the researchers write. “Trying to turn fundamentally unreliable data into a valid and reliable output is statistical alchemy, no matter how sophisticated and complex the mathematical models.”
Given the difficulty of distinguishing the toxicity of one type of asbestos fiber from another when all are known to cause cancer, the most health protective course is to err on the side of caution, they say.
The researchers note that the Occupational Safety and Health Administration’s mandate is to take protective action based on the best available evidence. They cite a 1980 Supreme Court decision that OSHA does not have to calculate the exact probability of harm before acting, and “so long as they are supported by a body of reputable scientific thought, the agency is free to use conservative assumptions in interpreting the data… risking error on the side of over protection rather than under-protection.”
While improving analytic methods and developing more precise understanding of the risk of various types of by asbestos fiber remain valid research pursuits, the researchers say the only way to stop asbestos-related disease is to stop the use of all types of asbestos.
##
