SCIENTIFIC Studies

  • Mortality from Occupational Exposure to Relatively Pure Chrysotile: A 39-Year Study

    09/10/2008 14:36:00

    Sichletidis studied the disagreement that exists regarding the relationship between chrysotile exposure and mesothelioma or lung cancer. To do this he looked at the cause of death in workers who had been exposed to relatively pure chrysotile in an asbestos cement factory where the asbestos fibre concentration was always below permissible levels. The date and cause of death were recorded for active and retired workers. Fifty-two workers died during the study, 28 from cancer of which 16 had lung cancer. No case of mesothelioma was reported. The authors concluded that occupational exposure to relatively pure chrysotile within permissible levels was not associated with a significant increase in lung cancer or with mesothelioma.

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  • Chrysotile as a Cause of Mesothelioma: An Assessment Based on Epidemiology

    06/01/2006 12:14:00

    One of the most important, recent, epidemiological papers is by Yarborough. His study not only shows that: “[A] review of 71 asbestos cohorts exposed to free asbestos fibers does not support the hypothesis that chrysotile, uncontaminated by amphibolic substances, causes mesothelioma. He also notes that failure to resolve the debate has hampered proper risk assessments: “A firm understanding of any health risks associated with natural chrysotile fibers is crucial for regulatory policy and future risk assessments of synthesized nanomaterials.” The paper underlines that the current mess of regulations and mis-understanding is a reflection of public policies not science.

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  • The expected burden of mesothelioma mortality in Great Britain from 2002 to 2050

    06/01/2005 14:56:00

    This more recent analysis by Hodgson and others modelled the expected burden of mesothelioma mortality in Great Britain based on male mesothelioma deaths from 1968 to 2001 as a function of the rise and fall of asbestos exposure during the 20th century and took into account the difference between fibre types. The models fitted the data to predict exposure patterns compared with the actual exposure patterns based on imports of amosite and crocidolite. The authors now state that chrysotile had zero weight in both the models they constructed. This means that, based on their work, the mesothelioma cases in Great Britain since 1920 can be explained by exposure to a combination of amosite and crocidolite.

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  • The Quantitative Risks of Mesothelioma and Lung Cancer in Relation to Asbestos Exposure

    06/01/2000 14:55:00

    The 2000 paper by Hodgson and Darnton, HSE statisticians, was welcomed by some but heavily criticised by many respected asbestos scientists. However, this work remains the information source of choice for the HSE, politicians and others. Its good point is that it clearly differentiates the specific risk of mesothelioma between the major asbestos types ranking their relative potency as 1:100:500 for chrysotile, amosite, crocidolite respectively. However, the reasons for giving chrysotile even this level of affect are considered by many to be flawed because of the way in which they assessed certain cohorts and it is noticeable that in a later paper chrysotile is removed from the discussion.

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  • Asbestos exposure and mesothelioma in South Africa

    06/01/1999 15:02:00

    In the mesothelioma literature South Africa is known for its crocidolite mines through the seminal paper by Wagner (1960) which identified this rare tumour in people living and working in or near the mines. It is less well-known that South Africa also has chrysotile mines which for decades produced about 100 000 tons of the mineral per year. Mesothelioma has not been found in the miners and millers who worked in these mines. Lees proposes that the for the scarcity or absence of the cancer may be a relative lack of contaminating fibrous tremolite, an amphibole that variably occurs with chrysotile ores.

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  • Asbestosis: A Marker for the Increased Risk of Lung Cancer Among Workers Exposed to Asbestos

    06/01/1999 12:18:00

    While the main cause of lung cancer at the present time is cigarette smoking it can also result from occupational exposure to asbestos. Weiss reviewed studies of lung cancer in groups of workers who had been exposed to asbestos and developed asbestosis. He found that the studies indicated that asbestosis is a much better predictor of excess lung cancer risk than measures of exposure and could be used as a marker for lung cancer cases attributed to asbestos.

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  • The 1891-1920 birth cohort of Quebec chrysotile Miners and millers: development from 1904 and Mortality to 1992.

    06/01/1997 14:45:00

    The largest epidemiological study in the asbestos industry was that of the miners and millers (those who crush the rock and extract the fibres) in Southern Quebec. Some 11,000 males born between 1891 and 1920 who worked in the industry were studied. Inevitably the researchers lost track of some of the men – there had been 1 or 2 world wars in their lifetime and some only worked for a few weeks and moved on. In total 9780 men were traced up to 1992. 1992. Of these, 8009 (82%) were known to have died: the most common causes of death were heart disease and stroke, which accounted for 3305 deaths (41.3%), followed by lung cancer (657, 8.2%), 38 died from mesothelioma, 1205 from other malignant disease, 108 from pneumoconiosis and 561 from other non-malignant respiratory diseases (excluding tuberculosis). Most of the cancer deaths could be attributed to smoking. The mines where they worked were grouped around either the town of Asbestos or the town of Thetford Mines. Of the 38 deaths from mesothelioma in the cohort, 33 were in miners and millers—25 from Thetford Mines and 8 from Asbestos, and the remaining 5 were in an associated asbestos products factory. Those from Thetford mines were mostly from the areas found to be contaminated with tremolite ( a fibrous mineral similar to crocidolite). These men, born 1891-1920, had worked through years of very high dust exposure yet with no discernible effect on mortality from lung cancer below an accumulated exposure of about 1000 (fibres/ml) x years and no case of mesothelioma among over 4000 men employed for less than 2 years. The authors concluded that their studies of the Quebec chrysotile miners and millers consistently showed little evidence of a cancer risk except at very high levels of exposure.

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