Asbestos : Update and assessment of the airborne exposure data used in the Hodgson and Darnton meta-analysis and its effects on the estimates of the cumulative exposure

The aim of this work was to re-examine and update the airborne sampling data for some of the pivotal epidemiological studies that contribute to the dose response relationships in the quantitative meta-analyses of risk from airborne asbestos exposures. The analysis by Berman and Crump (2004) and Hodgson and Darnton (2000), in particular, looked at the sampling data available and combined this to calculate the cumulative exposure. In the case of the Hodgson and Darnton (H&D) analysis, this was derived as a single figure for the cohort in terms of fibres-years /ml by a number of ways depending on the information available. This included multiplying the estimated arithmetical average airborne fibre concentration based on phase contrast microscopy (PCM) fibre count index by the average duration of the exposure, the mid-point of the range of exposures or by weighing separate exposure groups by the expected deaths from lung cancer. Berman and Crump (2004) assigned a risk to the quality of the data available and consistently the airborne fibre concentrations came out as by far the highest level of uncertainty. This and subsequent discussions at the WATCH meeting in November 2007 lead to a work item to look further into the H&D meta-analysis to determine the robustness of the key points. Examination of the air concentration data was one of the assessments to be undertaken.