Examination of the various studies produced and funded by the asbestos industry show a long history of manipulation of scientific data to postulate that anything but chrysotile causes mesothelioma. Time is against them, however, as between 85% and 95% of all asbestos used commercially was chrysotile. Despite the fact that other forms of asbestos have long since been banned mesothelioma cases continue to be diagnosed and many of those cases we now see were only ever exposed to chrysotile.
In 1965, the English epidemiologist Sir Austin Bradford Hill established a criteria consisting of a group of conditions necessary to provide adequate evidence of a causal relationship between an incidence and a possible consequence. Bradford Hill’s criteria are still accepted for investigating and defining causality in epidemiological study.
The list of criteria is as follows:
- Strength: Size of effect in a study.
The medical and scientific community universally accept that the overwhelming majority of mesotheliomas are caused by exposure to asbestos. Numerous studies of workers exposed to chrysotile demonstrate that the risk of contracting mesothelioma after exposure is more than double the risk of workers who have not been exposed.
- Consistency: Effect shown to be repeated in different conditions.
Cases of mesothelioma have been observed in chrysotile miners and workers throughout the world.
- Specificity: A specific site and specific condition without other likely explanation.
Specific condition would include all asbestos related disease, mesothelioma, lung cancer, asbestosis and pleural thickening, all can be caused by exposure to chrysotile.
- Temporality: Cause precedes the effect.
Given the latency period, the exposure to chrysotile will precede the development of mesothelioma.
- Biological Gradient: Greater exposure gives rises to greater incidence of the effect.
An increase in dose increases risk of disease. Any exposure to chrysotile raises the risk of development of mesothelioma.
- Plausibility: Mechanism between cause and effect.
It is known that all asbestos causes mesothelioma. It is known that chrysotile is carcinogenic and is a cause of mesothelioma.
- Coherence: Any inconsistency with epidemiological findings.
No clinical argument has been raised that explains why chrysotile cannot cause mesothelioma.
- Experiment: Laboratory evidence to support or deny.
Laboratory studies confirm that chrysotile can cause mesothelioma in rats. In studies chrysotile has been shown to be more carcinogenic in lab animals than other forms of asbestos.
- Analogy: Effect of similar factors to be considered.
All asbestos fibres cause mesothelioma. Chrysotile exposure on its own can cause mesothelioma.
On the basis of the Hill causation model chrysotile can cause mesothelioma.
Previous asbestos industry claims that mesothelioma following chrysotile exposure was only caused by contaminants in chrysotile do not appear sustainable. Studies with “pure” chrysotile have shown that this form of asbestos can also cause mesothelioma in lab animals. In addition the extent of any such contamination is minute. Far less than the 2% of exported crocidolite (blue asbestos banned in 1984) that the industry previously blamed for the cause of mesothelioma. Globally over 100,000 people still die annually from asbestos disease and given that over 85% of asbestos used commercially was chrysotile it would seem unlikely that all have been killed by the far smaller percentage of other asbestos used or by any small element of contamination.
A cynic might suggest that claims of the safety of chrysotile backed by asbestos industry friendly and funded research is solely to protect the industry’s main asbestos product and its continued use in the US and developing countries.
A director for the Bendix Corporation (now Honeywell) perhaps best summed up the industry view in a memo written in 1966 to an official with the Johns Manville Co in Canada (a chrysotile mine) in relation to the deaths of their workers:
“My answer to the problem is: if you have enjoyed a good life while working with asbestos products why not die from it.”