Chrysotile Asbestos Exposure linked to Lung Malignancy
Asbestos was once widely used worldwide. With the realization of health hazards associated with asbestos exposure more than 52 countries have either banned or restricted the use of asbestos. Unfortunately the mining and use of asbestos is continuing in developing countries like India and China. In India alone, the use of asbestos has doubled over the past decade and more than 100000 workers are exposed to this mineral.
Asbestos, chemically fibrous hydrated magnesium silicate occurs in two fiber varieties; serpentine and amphiboles. The serpentine chrysotile is spiral in shape while the amphiboles; crocidolite, amosite, tremolite are long and needle shaped. One of the long held views is amphiboles are more carcinogenic than serpentines. This premise better known as ‘amphibole hypothesis’ attributes carcinogenicity to the physical property of the fibre rather than the chemical composition. The long needle like amphiboles that can more easily penetrate the lung to the pleural surface are considered more carcinogenic. Malignancies that occurred with the chrysotile exposure were attributed to the natural contamination with tremolite, an amphibole. This hypothesis led to widespread acceptance of chrysotile asbestos in manufacturing industries.
A prospective 37 year follow up study from a chrysotile asbestos manufacturing unit in China shows that the risk of lung cancer and non-malignant respiratory diseases were three fold higher in workers exposed to chrysotile asbestos than controls. This strongly establishes the fact that exposure to chrysotile indeed increases the risk of lung malignancies. Smoking was found to further increase the risk of malignancy.
One of the findings of the study was that the incidence of mesothelioma was relatively low compared to other lung malignancies. This may suggest that probably in mesothelioma the fibre type may be a factor in the development of malignancy. It may be surmised that though the risk of mesothelioma is less with chrysotile variety, the risk of other lung malignancies is equal to that of amphibole variety.
Other than malignancies asbestos exposure is known to cause several respiratory diseases including pleural plaques, pleural thickening, pleural effusion and asbestosis. Asbestosis is characterised by interstitial inflammation and fibrosis and no drug is found to be of use in treating this disorder.
Increasingly the scientific community is of the consensus that there is no difference between lung cancer risks of different fibre types of asbestos. According to WHO more than 107,000 people die each year from asbestos related lung cancer. Findings of this study should be a wakeup call for policy makers in developing countries like India and China to stop mining and use of asbestos regardless of whether it belongs to chrysotile or amphibole variety.