The differential potency for causing mesothelioma among asbestos varieties is well established. In the year 2000, John Hodgson of the Epidemiology and Medical Statistics Unit, in the British Health and Safety Executive, published an analysis of the relative potency for different asbestos minerals. The published analysis showed that the estimated ratio of excess mesothelioma mortality for the same exposure in fiber/milliliter – years was 1:100:500 for chrysotile, amosite and crocidolite, respectively.[1] The analysis was recently updated by David Garabrant, who charitably considered some mixed exposure cohorts as chrysotile only,[2] with the result of slightly less extreme relative risks for amosite and crocidolite.[3]
The lawsuit industry’s expert witnesses have long been afraid to acknowledge the differential potency of chrysotile (with or without tremolite contamination) and the commercial amphibole fibers, amosite and crocidolite.[4] Why? First, by lumping the fiber types together, they obtain risk ratios for mesothelioma for all workers, regardless of the nature of their specific exposures. Their quest to seek compensation and obtain bans of all asbestos works better by simplification and exaggeration of risk. Second, they knew in the early days of the asbestos litigation in the United States that the South African amphibole suppliers were beyond the reach of courts and litigants in American courts. They were alert to the litigation risk that the Canadian mining companies would escape liability because the overwhelming bulk of the risk derived from South African amphibole fiber. Later cases involved chrysotile-only products that did not cause the level of exposures seen from friable insulation and cloth materials. A differential in risk for low-exposure chrysotile products raised serious questions whether such products could contribute substantially to a given case of mesothelioma, for which there was also exposure to amosite and crocidolite. Interestingly, some companies, concerned about losing contribution from low-exposure chrysotile products, took similar positions. Third, the exaggerated risks of all fibers helps advance their “each and every fiber” (or cumulative) causation theory, which they invoke to claim that even fleeting exposures from asbestos-containing products are “substantial contributing factors.” Consider how that argument goes when one product is akin to drinking 750 ml. of whiskey, and another is the equivalent of 1.5 ml. A man drinks a fifth of whiskey at one bar, and a thimble full of whiskey at the second. Most juries can see that the thimble was not substantial factor in contributing to the man’s drunkenness. Still, if you were the company that sold the whole bottle, you would love to have the thimble seller pay a 50% share; no? If you were the drunkard, and the seller of the bottle of whiskey was now a “bankruptcy trust,” obtaining a pro-rate share against the thimble seller would be lovely.
The extent to which crocidolite asbestos contributed to the horrific burden of mesothelioma was muddled by the writings of Irving John Selikoff. Before Selikoff wrote anything about any asbestos type and cancer, in 1960, in a remarkable case series, Christopher Wagner and colleagues showed a strong relationship between mesothelioma and crocidolite (blue) asbestos. Selikoff may not have had any first-hand knowledge of the unique potency of “big blue,” but he had been a regular testifier in workman’s compensation cases for UNARCO (Union Asbestos & Rubber Company) workers throughout the 1950s.[5]
In a 1965 volume, which Selikoff edited, of proceedings of a 1965 conference, which which Selikoff chaired, Selikoff presented United States Department of Commerce statistics that showed for six years reported (1957-1962), crocidolite imports exceeded amosite imports.[6] In that same year, 1965, in a prominent article in the New England Journal of Medicine, Selikoff played down the role in causing mesotheliomas in the United States.[7]
“Crocidolite is a relative newcomer to the American asbestos-industry scheme. Thus, American imports of crocidolite (none is mined here) were less than 500 tons in 1935 and had reached a level of only 20,000 tons even in 1962. In contrast, chrysotile, the type of asbestos fiber widely used in the American asbestos industry, was imported at a level of 165,000 tons in 1935 and 650,000 tons in 1962.5”
Selikoff thus chose to paint the mesothelioma problem as a dichotomy between blue asbestos and chrysotile, while leaving amosite out of the analysis completely. Indeed, the word “amosite” (or the word grunerite) does not appear in the New England Journal of Medicine article .
Aside from misleadingly framing the South Africa experience as limited to blue asbestos, and the United States experience as somehow limited to chrysotile, Selikoff presented the import statistics for amosite and crocidolite in a rather confusing way. In 1972, Selikoff presented a more revealing set of statistics about amphibole fiber imports, in the context of discussing whether amosite was carcinogenic (despite testifying in the UNARCO cases two decades earlier):
“Few data exist concerning the comparative neoplastic potential of the several kinds of asbestos in man. Some information is available for chrysotile,4 crocidolite,5 and anthophyllite.6 However, there has been no evidence to indicate whether or not the amosite variety is also carcinogenic.”[8]
Selikoff went on, in this 1972 article, to present more complete data on fiber type consumption in the United States, although still only estimates:
The 1972 article raises interesting questions about Selikoff’s own testimony in the 1950s New Jersey workman’s compensation cases on behalf of UNARCO workers. Table 1, reproduced above from Selikoff’s 1972 article, also throws considerable doubt upon generalizations about what fiber types were commercially used by insulators and others throughout the 20th century, in the United States. We can see that for 1920 and 1925, there is an “other” category, which could be virtually anything, and no data about South African fibers, which could mean none or it could mean simply no data available. In 1930, 1935, and 1940, there are data for crocidolite and amosite combined. Throughout the 1930s, the “other” category grew considerably, introducing serious ambiguity and doubt into Selikoff’s argument. Selikoff’s 1965 article in the New England Journal of Medicine gave a distorted view of the supply issue, but to my knowledge, it has never been corrected.
From Table 1, above, we see crocidolite and amosite data segregated for the first time in 1945. And for that year, the supply of crocidolite (8,700 tons) was almost twice that of amosite (4,500 tons). There was certainly no warrant for claiming that insulators and American factory workers had no amosite or crocidolite exposure before and after World War II.
While these confusions were being put forward, other countries were acting to control the occupational hazards of asbestos by differentially banning crocidolite, and imposing stricter controls on chrysotile. Selikoff led the United States in a different direction. The photograph and text below is from the May 1966 issue of the Port of Houston Magazine, showing how blue asbestos was continuing to invade the United States, while Selikoff and many of his colleagues were pointing to chrysotile.
Port of Houston Magazine 21 (May 1966)
In a 1968 conference presentation, with the benefit of hindsight, Selikoff addressed the issue of the forseeability of widespread asbestos disease:
“At the outset of this presentation, I questioned whether asbestos might properly be included as an unanticipated environmental hazard. Yet the less iconoclastic among us might have countered with: it must have been-we could not have knowingly allowed this to come to pass! Surely the explanation lies in the length of the period that elapses between exposure and disease which kept us from really knowing the problem until now.
Perhaps so. Indeed, I do not share the demonological theory of industrial hygiene history, in which industry is seen as callously exchanging human disease for profits. Rather, I would say industry shared the ignorance and lethargy of us all. The answer will come in these next several years. We have some reason for optimism. First, we have the law of averages on our side-sooner or later, some important environmental hazard is bound to be controlled. I suspect asbestos will be one. We have reason to believe that the dose-disease relationship is on our side-to the present, disease has been uncommon except with significant exposure. And our data suggest further that such significant exposure can be prevented, that we can learn to live and work with asbestos. All it will take is the doing -but herein lies another tale.”[9]
Selikoff’s position was especially generous to manufacturers who had used crocidolite after 1960, when Wagner alerted the community to para-occupational mesothelioma cases from blue asbestos exposure. Selikoff’s dismissal of the problem of blue asbestos as somehow a problem of English workers allowed the reality of blue asbestos use to be ignored, and then hidden with the myth of equal potency among all asbestos types. Twenty years after Selikoff’s New England Journal of Medicine article, no less an authority than Dr. Harriet Hardy would refer to mesothelioma as
“A fatal malignancy [mesothelioma] associated with inhalation of a single form (crocidolite) of asbestos invaded the chest wall (pleura) and/or the abdominal wall.”[10]
It is time to acknowledge the harm caused by asbestos fiber type egalitarianism.
[1] John T. Hodgson & Andrew A. Darnton, “The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure,” 14 Ann. Occup. Hygiene 565 (2000).
[2] Misty J Hein, Leslie T Stayner, Everett Lehman & John M Dement, “Follow-up study of chrysotile textile workers: cohort mortality and exposure-response,” 64
Occup. & Envt’l Med. 616 (2007).
[3] David H. Garabrant & Susan T. Pastula, “A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans,” 361 Toxicology & Applied Pharmacol. 127 (2018) (“relative potency of chrysotile:amosite:crocidolite was 1:83:376”). See also D. Wayne Berman & Kenny S. Crump, “Update of Potency Factors for Asbestos-Related Lung Cancer and Mesothelioma,” 38(S1) Critical Reviews in Toxicology 1 (2008).
[4] “Playing Hide the Substantial Factors in Asbestos Litigation” (Sept. 27, 2011); “Selikoff and the Mystery of the Disappearing Amphiboles” (Dec. 10. 2010).
[5] “Historians Should Verify Not Vilify or Abilify – The Difficult Case of Irving Selikoff” (Jan. 4, 2014); “Selikoff and the Mystery of the Disappearing Testimony” (Dec. 3, 2010).
[6] App. 3, Statistical Tables – Asbestos, prepared by T. May, United States Bureau of Mines, in I.J. Selikoff & J. Churg, eds., “Biological Effects of Asbestos,” 132 Ann. N.Y. Acad. Sci. at 753, Table 17 (1965).
[7] Irving J. Selikoff, Jacob Churg, and E. Cuyler Hammond, Relation Between Exposure to Asbestos and Mesothelioma, 272 New Engl. J. Med. 560 (1965).
[8] Irving John Selikoff, E. Cuyler Hammond & Jacob Churg, “Carcinogenicity of Amosite Asbestos,” 25 Arch. Envt’l Health 183, 183 (1972). The article contains no disclosure of conflicts of interest, despite Selikoff’s testifying role in UNARCO and other asbestos cases for claimants.
[9] Irving John Selikoff, “Asbestos” 11 Environment 3, 7 (Mar. 1969) (presented at the Symposium on “Unanticipated Environmental Hazards Resulting from Technological Intrusions,” held by the American Association for the Advancement of Science Committee on Science in the Promotion of Human Welfare and the Scientists’ Institute for Public Information, at Dallas, Texas, on Dec. 28, 1968).
[10] Harriet Hardy, M.D., Challenging Man-Made Disease: The Memoirs of Harriet L. Hardy, M.D. 95 (1983). See also “Harriet Hardy’s Views on Asbestos Issues” (Mar. 13, 2013).
