07/28/2011

Applying Quality Criteria to Exposure in Asbestos Epidemiology Increases the Estimated Risk

Asbestos is a well-known carcinogen responsible for cancer of the pleura and
peritoneum (mesothelioma) and lung cancer. The profound consequence of
historical exposure to asbestos is well documented in many countries. In all
Western countries, the pleural mesothelioma incidence among men has increased
dramatically in the past 40 years. In recent years, in some countries, a
leveling off of mesothelioma rates has been observed, whereas in most
countries, the mesothelioma incidence is still expected to rise in the next few
years. Asbestos is most likely the occupational risk with the highest burden of
disease.

Mesothelioma deaths due to environmental exposure to asbestos in The
Netherlands led to parliamentary concern that exposure guidelines were not
strict enough. The Health Council of the Netherlands was asked for advice. Its
report has recently been published. The question of quality of the exposure
estimates was studied more systematically than in previous asbestos
meta-analyses. Five criteria of quality of exposure information were applied,
and cohort studies that failed to meet these were excluded. For lung cancer,
this decreased the number of cohorts included from 19 to 3 and increased the
risk estimate 3- to 6-fold, with the requirements for good historical data on
exposure and job history having the largest effects. It also suggested that the
apparent differences in lung cancer potency between amphiboles and chrysotile
may be produced by lower quality studies. A similar pattern was seen for
mesothelioma. As a result, the Health Council has proposed that the
occupational exposure limit be reduced from 10 000 fibres m-3 (all types) to
250 f m-3 (amphiboles), 1300 f m-3 (mixed fibres), and 2000 f m-3 (chrysotile).
The process illustrates the importance of evaluating quality of exposure in
epidemiology since poor quality of exposure data will lead to underestimated
risk.


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AplusA-online.de - Source: The Annals of Occupational Hygiene