Retrospective occupational hygiene assessments.

In retrospective occupational epidemiological studies there is a need to make assessments of personal exposure which are valid over the whole period under study. Generally this process is complicated because of the absence of reliable historical concentration measurements, on which exposures could be based. This paper reviews the various strategies which have been used to estimate exposure in such circumstances. From this basis a systematic procedure is outlined to enable exposure estimates to be made. Many approaches have been adopted to make exposure assessments for retrospective epidemiological studies. For some situations monitoring data exist for all or part of the period under study. In the majority of cases little or no monitoring data are available and the most common approach has been to make a subjective estimate of exposure. The procedure outlined in this paper is intended to be used where good information about past concentrations does not exist. It begins with the identification of sources of exposure and the factors which may affect these. The historical development of the work process and environment should then be documented, in terms of these factors. The concentration of the substance can then be estimated by developing a mathematical model, integrating the workplace history with changes in the exposure factors and using current concentrations as a starting point. An essential final step in the process of exposure estimation is the validation of the model. This may be achieved by simulating an old work environment or through some other means. The approach advocated in this paper is exemplified in a study to estimate historical airborne fibre concentrations in the European man-made mineral fibre (MMMF) production industry.