Response to Murray M. Finkelstein, letter to the editor re Bernstein et al: Health risk of chrysotile revisited. Crit Rev Toxicol, 2013; 43(2): 154–183

• Amphibole asbestos
• chrysotile
• epidemiology
• health risk
• toxicology

Finkelstein, Murray M. – (BTXC-2013-0047) in his Letter to the Editor states that “surprisingly, Bernstein and colleagues completely ignore the human lung burden studies that refute the conclusions about the short biopersistence of chrysotile”.

However, the studies that Finkelstein, Murray M. (BTXC-2013-0047) cited (Churg et al., 1984; Churg & Wiggs, 1986; Dufresne et al., 1996; Rogers et al. 1991) appear to support the concepts put forward by Bernstein et al. (2013). As stated in those publications, all of the studies involved mixed exposure of amphibole asbestos with chrysotile with exposures dating from the first half of the 20th century before controlled use was implemented.

The toxicology studies that Bernstein et al. (2013) cites explain two very important aspects which are relevant to interpreting the studies cited by Finkelstein. When amphibole fibers are present in the lung, the intense inflammatory response created by the longer fibers has been shown to effectively lock up the shorter fibers, so that they do not clear as well. In humans exposed to both amphibole fibers and chrysotile, a similar process would occur in which the chrysotile would be bound in the inflammatory matrix created by the amphibole fibers. Fibers within this matrix would not clear very quickly and could have clearance half-times approaching that of amphibole fibers completely in agreement with what is stated. Secondly, as also shown in the studies by Bernstein et al., which have used confocal microscopy to determine the localization of fibers within the lung and pleural cavity, fibers are translocated to different regions within the lung. In particular, the shorter chrysotile fibers can be translocated to the lymphatic system where they accumulate over time within the bronchial associated lymphoid tissue and the lymph nodes. This is the same process for any relatively insoluble innocuous dust which will accumulate in the BALT and lymph nodes and persist over time. As all the studies cited by the author used a lung digestion procedure to analyse the fiber content, and were with exposures at high concentrations, it would be impossible from these studies to determine where the fibers were within the lung.

In addition, numerous fiber burden studies have shown that the risk of mesothelioma correlates with amphibole and not chrysotile fiber levels (these include Churg & Vedal, 1994; Howel et al. 1999; Wagner et al., 1988). The chrysotile miners and millers that Churg studied did not necessarily cease exposure to chrysotile when they ceased employment since they presumably lived in the vicinity of Asbestos or Thetford which have increased ambient levels of chrysotile asbestos. The controls that he used for the studies were from the Vancouver area.

The study of Rees et al. 2001 of asbestos lung fiber concentration in South African chrysotile mine workers revealed relatively low concentrations of chrysotile fiber implying substantial clearance. In fiber burden studies of friction product workers, elevated levels of chrysotile fibers have not been found unless there were concomitant increases of commercial amphibole fibers (Butnor et al., 2003; Woitowitz & Rödelsperger, 1994).

Finkelstein further states that “By failing to mention any of the data which contradict their conclusions, Bernstein and colleagues have clearly not provided an objective analysis, and have created the impression that they have published a document to support the interests of the International Chrysotile Association, which, in cooperation with The Canadian Chrysotile Association, funded their work”.

However, the data cited by Finkelstein do not contradict the concepts put forward by Bernstein et al. and in fact they appear in company with an understanding of the toxicology to clearly support these concepts.

Finally, Finkelstein refers to the funding of the Bernstein et al. review by the Canadian Chrysotile Association, stating that “they have published a document to support the interests of the International Chrysotile Association”. In his own Declaration of Interest, Finkelstein declares that “The author has appeared as an expert witness in litigation concerned with alleged health effects of exposure to chrysotile”. What Finkelstein has left unstated is the frequency with which he works for the plaintiff’s lawyers who would benefit from publication of his Letter to the Editor.

Declaration of interest

The preparation of the original paper was supported by a fixed sum grant from the International Chrysotile Association, Washington, DC, USA, in cooperation with The Canadian Chrysotile Association, Montréal, QC, Canada. The affiliation of the authors includes university, government institute, hospital and corporate affiliations as well as independent toxicology consultants. This letter is the professional work product of the authors alone and may not necessarily represent the views of the corporate sponsors. Two of the authors, David Bernstein and Allen Gibbs have appeared as expert witnesses in litigation concerned with alleged health effects of exposure to chrysotile. Jacques Dunnigan has served as an expert witness on the health effects of chrysotile before the Commission de la santé et sécurité du travail du Quebec/Workers Compensation Board of Québec.