Chyrsotile Amphibole Asbestos -
Chrysotile Asbestos, Amphibole
What is Mesothelioma?
"Mesothelioma (malignant)"
Mesothelioma is a rare form of cancer. It affects the linings of the cavities around the lungs, stomach, and heart. It is caused by inhaling asbestos fibers, but the cancer usually does not appear until 10 to 40 years after a person first inhales asbestos.
Chrysotile - Amphiboles
Table 3 shows the EPA's inconsistency in the approach to carcinogenic potency of different asbestos fibres. It shows modified values of the coefficient KL, taken from an EPA publication (36), indicating considerable differences in the potency of different asbestos fibres.
The coefficient KL reflects the carcinogenic potential of the exposure to carcinogens; it is the estimated increase in lung cancer risk due to one-year exposure to the unit concentration of 1f/ml. The values presented in Table 3 clearly show that the carcinogenic risk is by far the lowest in the exposure to chrysotile only, with the exception of chrysotile in textile production.
Exposure to amosite fibres alone involves a much greater risk, as is the case with the combined exposure to amphibole asbestos and chrysotile asbestos. The high KL value in pure chrysotile textile production is attributed to a significantly higher content of more carcinogenic long chrysotile fibres in textile production (37-40).
Rich evidence of the significant difference in the potencies between fibres of chrysotile and amphiboles gave grounds for introducing 'the chrysotile hypothesis" and 'the amphibole hypothesis". The first says that the human risk becomes acceptable at a sufficiently low exposure level to chrysotile, and the second that the carcinogenic risk at low concentrations of chrysotile is present only if amphiboles are also present.
These hypotheses are not generally accepted; they have particularly been rejected by the US regulatory agencies (1,33) and by the Ramazzini Society (12,41). The controversy about whether there is a difference in the carcinogenic potency between chrysotile and amphibole fibres is continued in more recent papers by most reputable authors in the field.
While Berry (42), Landrigan and co-workers (43), and Dement (44) believe that chrysotile is less potent than amphiboles in its ability to cause mesothelioma, and Hodgson and Darnton (45) conclude that specific risks of mesothelioma from chrysotile, amosite and crocidolite are in the ratio 1:100:500, respectively, Landrigan and coworkers and Dement consider that the lung cancer risk from chrysotile is at least as high as that from amphiboles, and Smith and Wright (46) regard chrysotile as the main cause of pleural mesothelioma in humans.
While McDonald and McDonald (50) and McDonald (53) state that the carcinogenic risk at present day levels of exposure to commercial chrysotile is vanishingly small and that the remaining risk is due to contamination of chrysotile by the amphibole tremolite, Dement (44) maintains that chrysotile should not be controlled differently than other asbestos types.