Discussion
The above-mentioned publications of corporate affiliates put forth unreliable illness estimates and conclusions by omitting well established scientific facts, relying on incomplete and or outdated data, or omitting critiques of data sets relied upon, and drawing false conclusions due to use of data sets that are not adequately controlled for latency and/or exposure.
There is also the Vanderbilt talc issue-contaminated with asbestos - where a company official boasted to workers of having a “US Senator in our back pocket”.
As mentioned, there is absolutely no doubt among independent scientists that all asbestos types are carcinogenic and cause many diseases including mesothelioma. This was also IARC’s conclusion upon evaluation of the available literature [
92] as well as of other scientific organisations and societies [
11,
93‐
97]. Furthermore, exposure to chrysotile is also associated with the other typical asbestos-caused disorders - asbestosis and plural fibrosis [
3,
93‐
96,
98,
99]. The difference between diseases RRs (risk ratios) of chrysotile versus amphiboles has been debated and is considered by some to be a legitimate but unsettled issue. Some, but not all studies, provide evidence of differences of the various asbestos fiber types. In this connection recent publications by Lenters, Burdorf et al. [
100,
101] are worth mentioning. These authors had a closer look at the quality of asbestos exposure assessment; they came to the conclusion that differences between risks of chrysotile and amphiboles are mainly due to shortcomings in exposure assessment than in fiber types.
By summarizing the literature, Lemen [
102], Frank [
11] and Egilman [
103] demonstrate that chrysotile meets all of Hill’s nine proposed criteria of causation, i.e. of malignant mesothelioma. The same is true for the other asbestos-related cancers and for asbestosis. As for other asbestos types, no threshold could be demonstrated below which adverse health effects do not occur.
As mentioned, the counter argument that amphiboles frequently present in very low amounts in chrysotile products are responsible for the disorders found in exposed workers is not likely because the mostly very low or even absent amphibole contamination does not correlate with diseases. Studies in cohorts only exposed to chrysotile fibers such as from specific mines, textile industries, brake repairing, but not to amphiboles, exhibit the typical asbestos-related diseases, especially mesothelioma [
27,
104‐
109]; see also overviews by Lemen at al [
29]. and by Lemen 2004 [
102]. Frank et al. [
35] analyzed Canadian UICC chrysotile B which is free of tremolite by electron microscopy; they found that chrysotile was the only fibrous asbestos component. Very similar results were reported in miners and millers from Balangero, Italy, [
104], China [
110] or Zimbabwe [
106] exposed to amphibole-free chrysotile. In the former East Germany Republic DDR where much Russian chrysotile was used [said to be amphibole free], and sometimes only chrysotile was applied, hundreds of pleural and peritoneal mesotheliomas were recorded and written about [
111]. These findings correspond to chrysotile-induced pathology in animal studies which do not support an explanation based on the so-called “amphibole hypothesis”. The animal experiments showed that pure chrysotile is carcinogenic [
37,
38,
112‐
119]. Also in-vitro toxicological studies provided corresponding findings [
103].
The aforementioned well-founded outcomes of human and animal studies on adverse health effects of chrysotile as published by the IARC [
92], the Collegium Ramazzini [
120], and other authors [
27,
35,
53,
99,
101,
102,
115,
121‐
126] were all not cited in recent publications questioning these facts [
8,
30,
31,
127]. It has also been ignored that chrysotile, especially its short fibers, move to the pleura where high concentrations can be found in exposed subjects and animals, often with no presence of amphiboles [
21,
117,
128‐
131].
With regard to causative asbestos exposure, it is important that the level of exposure necessary to induce mesothelioma is well below the level necessary to induce asbestosis or other non-malignant asbestos-associated diseases [
95]. So it is not surprising that mesotheliomas have been documented not only in occupational settings but also in para-occupational settings such as those occurring among family members exposed to asbestos fibers introduced into the household through the clothes of the worker, and in the vicinity of asbestos manufacturing plants where fiber concentrations are much lower [
40,
132‐
134].
However, it should be mentioned that none of the efforts to use statistical models to characterize relative cancer potencies for asbestos fiber types and sizes have been able to overcome limitations of the exposure data. Quantification of the risk is not reliable because accurate exposure information is lacking for the epidemiological studies used such as Hodgson & Darnton [
32] and Berman & Crump [
33,
34]. Hodgson & Darnton [
135] explained that they relied on “guesstimate(s)” for a number of missing data points [
50]. By only referring to studies of earlier potency estimates reported by Hodgson and Darnton [
32].
The significantly revised later estimates lowering the potency differences between chrysotile and amphibole asbestos by these same authors (Hodgson and Darnton [
135] have been repeatedly ignored as already pointed out by (Lemen, Frank et al. [
29]. Resulting uncertainties have been so great that estimates should not be used to drive occupational and environmental health policy. The EPA rejected and discontinued work on its proposed methods for estimating potency factors. For more details see the EPA Report on the Peer Consultation Workshop to Discuss a Proposed Protocol to Assess Asbestos-Related Risk, at pages 3--14.: “
The risk coefficients (for mesothelioma)
were largely derived from data sets with inadequate exposure--response information for mesothelioma, and assumptions had to be made to determine critical inputs to the mesothelioma model (e.g., average exposure, duration of exposure)”.
Correspondingly, according to Silverstein, et al. [
136], an EPA Peer Consultation Workshop convened to review the 2003 version of the Berman & Crump approach yielded the following criticisms: “
The 2003 report repeated earlier cautions that grossly imperfect exposure characterization in the epidemiology studies creates substantial uncertainties in the estimation of potency factors, including both random and systematic biases. Among the specific data flaws mentioned were unrepresentative sampling strategies, use of surrogate measures in the absence of actual asbestos measure [
136]
.
Conclusions
The ongoing promotion of chrysotile combined with unjustified downplaying of its adverse health effects, especially of its carcinogenicity, is driven by commercial interests and is not supported by scientific evidence, see e.g. websites of ICA and its predecessor the Chrysotile Institute [
137,
138] and a related commentary [
4]. The same is true for widespread restrictive compensation practices based upon lung fiber counts or inadequate risk models [
139‐
141]. As an example, the aforementioned statement of predominantly non-asbestos causation of mesothelioma in women in a chapter in the WHO/IARC book accompanied by similarly distorted statements made by the same or other sponsored or affiliated authors in various journals, lacks scientific evidence and is not true.
A related example is the “amphibole hypothesis” originating from the Quebec industry-sponsored studies. Correspondingly, McCormack et al. [
28] and Gilham et al. [
13,
142] published that figures showing mesotheliomas related to chrysotile asbestos exposure may be erroneously overestimated, and that mesothelioma in chrysotile-exposed cohorts is due to other asbestos types. As mentioned, the literature shows the opposite [
35,
37,
92,
143].
The relative lack of chrysotile biopersistence in the lung combined with its translocation to the pleura and also to the peritoneum and pericardium where the mesothelioma develops has to be taken into consideration when interpreting fiber data in tissue and pathogenicity [
24,
128,
131,
144].
The aforementioned influence of vested asbestos-related interests in workers and public health issues including regulations and compensation necessitate ongoing alertness, corrections and appropriate reactions in scientific as well as public media and policy advisory bodies.
It should be mentioned that in general sophisticated mineralogical analysis of lung tissue is a useful method for determining the lung fiber burden when the occupational history does not allow a reliable exposure assessment. However, it has to be taken into consideration that there is considerable interlaboratory variation and it is essential that each laboratory establishes its own reference values [
63]. Thus, comparison of data obtained in different laboratories is difficult and this limits the proper use of mineralogical results in the legal field. Furthermore, as stated in the Helsinki criteria [
63] at negative non-effect outcome excludes neither potential past asbestos exposure nor the likelihood of asbestos-related disease to develop, while with positive results the possibility of a serious health consequence is increased [
145].
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14].