Many researchers have published analyses of the relative potency for the commercial asbestos fiber types to cause mesothelioma. Hodgson & Darnton (2000) is often cited for estimating the potency of crocidolite to amosite to chrysotile as 500: 100: 1. Berman & Crump (2008) estimate the amphiboles were more than 200 times more potent than chrysotile. More recently, Garabrant & Pastula (2018) updated the Hodgson & Darnton (2000) analysis with data published since 2000, estimating the relative potency as 376: 83: 1. But, even if the amphiboles are more potent than chrysotile on a fiber-per-fiber basis, some argue that the analyses still show that chrysotile is potent for causing mesothelioma. And, because chrysotile was so much more widely used than crocidolite and amosite, they argue it is still a significant cause of many mesotheliomas.
Responding to this argument calls for a closer look at the analyses and, in particular, the “chrysotile” studies reviewed to find any potency for mesothelioma. It is clear that all the studies purporting to find risk from chrysotile exposure involved co-exposure to amphibole asbestos and, where the co-exposure was a likely contaminant of the chrysotile, involved cumulative exposure exceeding 100 fiber-yrs.
– Ray Harris, Erin Therrian