Significant results from one of the largest asbestos inhalation studies ever done were never published. Over the last 10 years, some of these have been found and reported in a series of papers in this journal. The “missing” data from the study were largely concerned with the potential chronic effects of short fibre chrysotile but also dealt with the alleged ability of a single, high dose exposure to long fibre chrysotile to produce a risk of disease for life (so-called “irreversibility”). Given its ubiquity and the notion held by the US Government and Plaintiff that all forms of asbestos are equally potent in even the smallest doses, the where-withal to scientifically “exonerate” short fibre chrysotile as a human health hazard would have very major regulatory, socio-economic and legal implications. The US Government was aware that the issues of fibre length and irreversibility had to be scientifically resolved and so funded the study. California Coalinga chrysotile was used as the “standard” short fibre material for the chronic inhalation assay: initially a 12-month exposure to fibre and then lifetime follow up. The “irreversibility” question was tested with a long fibre chrysotile from the Canadian Jeffrey mine: an initial high dose 1-hour to 1-day exposure and then 2-year follow-up. This report summarises how some of these missing data were found and discusses their relevance.
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