Chrysotile as a Cause of Mesothelioma: An Assessment Based on Epidemiology
Charles M. Yarborough, Exponent, Inc., New York, New York, USA
There has been a longstanding debate about the potential contribution of chrysotile asbestos
fibers to mesothelioma risk. The failure to resolve this debate has hampered decisive risk communication
in the aftermath of the collapse of theWorld Trade Center towers and has influenced
judgments about bans on asbestos use. A firm understanding of any health risks associated with
natural chrysotile fibers is crucial for regulatory policy and future risk assessments of synthesized
nanomaterials. Although epidemiological studies have confirmed amphibole asbestos
fibers as a cause of mesothelioma, the link with chrysotile remains unsettled. An extensive review
of the epidemiological cohort studies was undertaken to evaluate the extent of the evidence
related to free chrysotile fibers, with particular attention to confounding by other fiber types,
job exposure concentrations, and consistency of findings. The review of 71 asbestos cohorts
exposed to free asbestos fibers does not support the hypothesis that chrysotile, uncontaminated
by amphibolic substances, causes mesothelioma. Today, decisions about risk of chrysotile for
mesothelioma in most regulatory contexts reflect public policies, not the application of the scientific
method as applied to epidemiological cohort studies.
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