The health effects of white asbestos
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Chrysotile is an established carcinogen and there is no safe threshold
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WHEN THE towers of the World Trade Center (WTC) in New York collapsed in September 2001, they released a cloud of hazardous material that included 2000 tonnes of asbestos.
In a ruling on a class action suit filed by people who say they were exposed to this hazard, on February 2, 2006, Judge Deborah Batts chastised the US Environmental Protection Agency for having first assured that the clouds were safe from asbestos and later admitting to this misinformation, calling their assurances as `conscience-shocking'.
The asbestos used at the WTC is what is known as `white asbestos' or chrysotile as it is chemically known. This form of asbestos is being used in the U.S., India and many other countries with the belief that of the various forms of asbestos, chrysotile is the safest.
The basic message
The Asbestos Cement Products Manufacturers Association of India (ASCMA), during the Clemenceau controversy, issued a public interest advertisement stating that (a) chrysotile or white asbestos, when used under controlled conditions, does not pose any risk to health (b) chrysotile fibres are locked as a 8-9 per cent component in a cement matrix which prevents them from escaping into the air, and (c) asbestos occurs in nature and a lot of asbestos fibres are inhaled by us everyday.
The basic message here is that chrysotile is used in India under controlled conditions and is therefore completely safe. Asbestos occurs in nature in six forms, broadly classified into two families. One is the amphiboles (or the two-sided) wherein the molecules form railway track-like double chains.
Blue Asbestos (or crocidolite) and Brown Asbestos (or Amosite) are two common examples.
The other is the serpentine family, best typified by chrysotile.
Source of controversy
These form extended sheets, which wrap around themselves into curved tubular structures (serpentine) in contrast to the `straight' amphiboles.
The chemical properties of all classes of asbestos are pretty much the same, but it is their relative health effects that have been a source of controversy.
There is a group that holds all asbestos — amphiboles or serpentines — are equally dangerous to human health; there is another, which has been staunchly holding that the culprits are the amphiboles, and chrysotile is safe.
The ASCMA belongs to this class of `chrysophiles' while the former are the `chrysophobes.' What is the latest in this confrontation between the two? An educative and remarkably readable analysis of the white asbestos controversy has been published by Drs. G. Tweedale of the Manchester Metropolitan University Business School, UK and J. McCulloch of the RMIT University School of Social Science and Planning at Melbourne, Australia.
Called the Chrysophiles versus Chryophobes, this paper in the journal Isis (2004, 95: 239-259) gives a historical account of the gory story where science was repeatedly given the short shrift by commerce.
No distinction made
Until the 1950s scientists, while admitting the health hazards of asbestos, made no distinction between its types in their ability to cause diseases. When in 1960, it was found by one Dr. J.C. Wagner in South Africa that blue asbestos caused malignant mesothelioma (cancer of the linings of the lungs, chest and abdomen), it caused a furore in the industry there.
Interestingly, since it was chrysotile that was the major asbestos of commerce and use in U.K. and U.S., industry seized blue asbestos as the culprit, declaring that white asbestos has not been similarly implicated and so it is safe.
Tweedale and McCullogh give a detailed history of how industry interests in U.S. and in particular Canada (a major world source of chrysotile) campaigned and raised funds for research purporting to show that chrysotile was safe.
As the Isis article points out, when covering the controversy in the period 1950-2004, political, economic and social factors have militated against a speedy resolution of the debate, facilitating the continued production and use of asbestos in the developing world. Let us now look at developments in the biomedical literature during the last few years.
Many published articles
The PubMed database, maintained by the US National Library of Medicine, cites 141 published articles in the last three years on the health effects of chrysotile and just about every one of them reports its ill effects on proteins and DNA, cells and tissues of the body.
Dr Qamar Rahman of the Industrial Toxicology Research Centre at Lucknow was one of the early ones to show how chrysotile induces oxidative stress in experimental animals (J. Biochem. Mol. Toxicol. 17, 366, 2003).
Later studies support her and show that it does so by producing reactive oxygen species, which damage cellular molecules and components. It damages DNA, producing 8-oxo-guanine, and it affects the cell cycle and proliferation of cells.
These effects are also seen to be specific to the cell type; mesothelial cells are specifically targeted by chrysotile, producing cancer there, while fibroblasts (cells that make up the connective tissue) are not (Kopnin and coworkers: Oncogene 23, 8834, 2004). Li and coworkers in Hangzhou, China did a meta-analysis (which combines the results of several studies addressing a given issue) of cancer mortality among workers exposed only to chrysotile (Biome. Environ. Sci. 17, 459, 2004), concluding that there are excessive risks of lung cancer and mesothelioma among workers exposed to white asbestos alone, and little association between its exposure and cancers at other sites. In other words, chrysotile affects the lungs and pleura specifically.
When discussing epidemiological associations of this type, rigour is provided only when all causal criteria are satisfied.
The British medical statistician Sir Austin Bradford Hill has listed nine such criteria: strength and association, consistency, specificity, temporality, dose-response, biological plausibility, biological coherence, experimental evidence, and analogy.
Causal factor
And, the former Assistant Surgeon General of USPHS, Dr. R.A. Lemen, has applied these nine to the chrysotile-mesothelioma connection (Int. J. Occup. Environ Health 10, 233, 2004), found them all satisfied, and concludes that chrysotile asbestos is not just associated with, but a cause of mesothelioma.
It has been held that controlled use of chrysotile makes it safer. It is interesting to note here that the Appellate Body of the World Trade Organization, in upholding the French ban on asbestos, ruled in 2000 that chrysotile is an established carcinogen, there is no safe threshold and `controlled use' is not an effective alternative to a national ban.
D. BALASUBRAMANIAN
dbala@lvpei.org
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