The role of fiber type and cumulative exposure in controlling mesothelioma risk.
Toxicology and Applied Pharmacology 2018 October 28 [Link]
Langer AM, Nolan RP
The acceptance of primary tumors arising on the serosal surface of body cavities and its association with asbestos exposure was established in 1960. Epidemiological studies followed in an effort to determine if all asbestos fiber types produced the same malignancy and with the same mortality incidence. Three asbestos mortality studies were published in 1979 authored by the same research team from the Mount Sinai School of Medicine. The studies followed the same design making their datasets internally consistent and uniquely comparable. Insulation workers who were exposed to three commercial fiber types (amosite, chrysotile, crocidolite), factory workers who manufactured amosite-containing insulation for U.S. warships, and chrysotile miners and millers from Thetford Mines, Quebec, comprised the three cohorts. Lifetime cumulative exposures for these three cohorts (expressed in fiber/mL-years) were available from different source materials. Mortality data were obtained on these workforces and ascertainment of their cause(s) of death was based on medical-pathology evidence rather than information available on death certificates. Depending on the exposure estimates for the three cohorts the calculated mesothelioma risk for mid range mixed fiber exposure (insulators) is about 269 times (range 157 to 490) that of chrysotile exposure alone and for amosite at mid range exposure about 139 times (range 30 to 213) that of chrysotile exposure alone. Risk comparisons are the result of range in cumulative exposure estimates. Based on the available data from three Mt. Sinai studies, these differences in mesothelioma risk regarding fiber type were apparently knowable to the asbestos community as early as 1979. The amphibole asbestos exposures carry far greater mesothelioma risk than chrysotile exposure alone. Mixed fiber exposure (chrysotile and amphibole asbestos) is associated with the highest mesothelioma mortality among the workforces studied.