Applying Quality Criteria to Exposure in Asbestos Epidemiology Increases the Estimated Risk
Health Council of the Netherlands was asked for advice by the Ministries of the Environment and of Social Affairs and Employment to provide scientific evidence on risks of environmental and occupational exposure to asbestos
14.07.2011 | Annals of Occupational Hygiene, June 2011. Alex Burdorf and Dick Heederik via IPEN
This commentary reports that the Health Council found that, when asbestos studies with low quality data are excluded, the risk estimate increases 3 to 6 times and that apparent differences between amphibole asbestos and chrysotile asbestos in causing lung cancer and mesothelioma are much less than previously thought.
The occupational exposure limit in The Netherlands for chrysotile asbestos is 0.01 f/cc. The Netherlands Health Council has recommended this be changed to 0.002 f/cc.
Kathleen Ruff, Roca alliance member from Canada states "Note that the Canadian government (like the governments of other asbestos exporting countries, such as Russia, Kazakhstan and Brazil) endorses the position of the asbestos industry that permits exposure levels of 1 f/cc, which is one hundred times higher than the present standard in The Netherlands".
Full commentary available here
Although quality aspects have been mentioned in earlier reviews on asbestos studies, quality was never systematically evaluated. This is a surprising finding, given the crucial role of epidemiological evidence in the guidelines for occupational and environmental exposure to asbestos. Since a poor quality of exposure estimates will inevitably lead to exposure misclassification and, thus, underestimation or misspecification of exposure–response relationships, the Committee decided to conduct a systematic review with quality appraisal and to analyse the influence of quality of the different studies on average effect estimates for asbestos and cancer.
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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