Applying quality criteria to exposure in asbestos epidemiology increases the estimated risk

Our plain-English summary of Applying quality criteria to exposure in asbestos epidemiology increases the estimated risk, by A. Burdorf, D. Heederik (The Annals of Occupational Hygiene, 2011).

The study

• Authors: A. Burdorf, D. Heederik
• Journal: The Annals of Occupational Hygiene
• Published: 2011;55(6):565-8
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

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.

In plain English

This commentary, by two members of the Health Council of the Netherlands' asbestos committee, described the Council's 2010 review of cohort studies of occupationally exposed workers. The committee rated the studies against five criteria for the quality of their exposure information. For lung cancer, 19 cohort studies were included. Excluding studies that failed the criteria on exposure-data coverage and job history raised the risk estimate 3- to 6-fold. Stepwise exclusion raised this estimate, 100 times KL (the slope of relative risk per fibre-year per millilitre of cumulative exposure), from 0.13 (19 studies) to 0.48 (3 studies). For mesothelioma, 12 studies gave risk estimates of 7.95 for amphiboles, 1.08 for mixed exposure and 0.017 for chrysotile. When the analysis was limited to the highest-quality studies, the estimates were 1.30 for mixed exposure and 0.15 for chrysotile. The Council proposed occupational exposure limits of 420 fibres per cubic metre for amphiboles (the abstract says 250), 1300 for mixed fibres and 2000 for chrysotile. The existing limit was 10 000 for all fibre types. The authors concluded that poor exposure assessment leads to exposure limits that do not protect workers.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Commentary describing a systematic review with quality appraisal and meta-analysis carried out by a committee of the Health Council of the Netherlands; the lung cancer analysis is published separately (Lenters et al., 2011)
• Who was studied: Selected cohort studies of occupationally exposed workers: 19 cohort studies for lung cancer and 12 studies for mesothelioma
• Exposure: Occupational asbestos exposure, analysed as amphiboles, mixed exposure and chrysotile; risk expressed per unit of cumulative exposure in fibre-years per millilitre
• Main results:
  • Lung cancer (19 cohort studies): excluding studies that failed the criteria on coverage of exposure data and job history increased the risk estimate 3- to 6-fold
  • Lung cancer: the measure used was 100 times KL, the slope of increase in relative risk per unit of cumulative exposure (fibre-years per millilitre). With stepwise exclusion of less informative studies, this estimate increased from 0.13 with 19 studies to 0.48 with 3 studies (reported from Lenters et al., 2011)
  • Mesothelioma (12 studies): risk estimates KM were 7.95 for amphiboles, 1.08 for mixed exposure and 0.017 for chrysotile
  • Mesothelioma, highest-quality studies only: risk estimates KM were 1.30 for mixed exposure and 0.15 for chrysotile. The highest-quality studies were those where workers had predominant or exclusive chrysotile exposure
  • The slopes of the exposure-response relationships were roughly 5 to 10 times higher than those in the meta-analyses of Hodgson and Darnton (2000) and Berman and Crump (2008)
  • The Health Council assumed an acceptable risk of one additional death from lung cancer or mesothelioma per 1 000 000 person-years among exposed workers. On that basis it proposed occupational exposure limits of 420 fibres per cubic metre for amphiboles, 1300 for mixed fibre type and 2000 for chrysotile. The existing Dutch limit was 10 000 fibres per cubic metre for all fibre types
• The authors' conclusion: The authors concluded that evaluation of exposure-assessment quality should be part of risk assessment. In their view, poor exposure assessment leads to occupational exposure limits that do not protect workers. They also stated that, for lung cancer, it cannot be excluded that the suggested potency differences between chrysotile and other asbestos types are entirely due to study quality

Topics

Medical terms in this study, explained in our Lexicon: Epidemiology, Mesothelioma, Environmental Exposure, Lung Cancer, Amphibole Group, Chrysotile, Occupational Exposure.

Related studies

• Overreliance on a single study: there is no real evidence that applying quality criteria to exposure in asbestos epidemiology affects the estimated risk — D.W. Berman, B.W. Case (2012)
• An air quality data analysis system for interrelating effects, standards, and needed source reductions: Part 13--Applying the EPA Proposed Guidelines for Carcinogen Risk Assessment to a set of asbestos lung cancer mortality data — R.I. Larsen (2003)
• Applying definitions of "asbestos" to environmental and "low-dose" exposure levels and health effects, particularly malignant mesothelioma — B.W. Case, J.L. Abraham, et al. (2011)
• A meta-analysis of asbestos and lung cancer: is better quality exposure assessment associated with steeper slopes of the exposure-response relationships? — V. Lenters, R. Vermeulen, et al. (2011)
• The potential impact of epidemiology on the prevention of occupational disease — D.H. Wegman (1992)
• Design and conduct of occupational epidemiology studies: IV. The analysis of case-control data — N. Pearce, H. Checkoway, et al. (1989)

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