Objectives Although an asthma-like syndrome has been recognised in aluminium smelter workers for over 70 years, the causal agent has been difficult to identify.
Methods An inception cohort study was conducted at two Australian aluminium smelters where 446 employees participated over a period of 9 years. Cumulative exposures between interviews were estimated from job histories using a task exposure matrix based on measurements in the smelters. Participants completed an MRC respiratory questionnaire, spirometry and methacholine challenge test. Data were analysed with generalised estimating equations to allow for repeated measurements of each participant.
Results Wheeze and chest tightness, the two symptoms most closely related to asthma, showed associations with occupational exposures. SO2 exposure was significantly associated with these symptoms, bronchial hyper-responsiveness (BHR) to methacholine (a feature of asthma), airflow limitation (reduced forced expiratory volume in 1 second/forced vital capacity ratio) and longitudinal decline in lung function. Fluoride exposure was associated with the same outcomes, but less strongly. Inhalable dust and the benzene soluble fraction (BSF) were associated with symptoms of asthma and BHR. Although many of the exposures were highly correlated, further modelling suggested that of the known respiratory irritants, SO2 was more likely than fluoride to be primarily responsible for the symptoms observed. Fluoride, inhalable dust and SO2 were the most important airborne contaminants associated with effects on lung function.
Conclusions The observed effects were detected at contaminant levels within occupational exposure standards, so further reductions are required, particularly in SO2 exposures.
- Aluminium smelting
- sulphur dioxide
- occupational asthma
- bronchial hyper-responsiveness
- exposure assessment
- longitudinal studies
- lung function
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Funding The Healthwise study was funded by Alcoa of Australia Ltd (PO Box 252, Applecross WA 6953). The sponsor had no direct involvement in study design, the collection, analysis and interpretation of data, the writing of the report or in the decision to submit the paper for publication. Geza Benke and Lin Fritschi are supported by the National Health & Medical Research Council of Australia.
Competing interests Malcolm Sim is the principal investigator of the Healthwise programme of studies, which is funded by Alcoa of Australia A$700 000 per year. This research grant is paid to Monash University and the University of Western Australia and is used to pay for research staff who work on the study and other direct research costs. Malcolm Sim was also an invited keynote speaker at an aluminium industry-sponsored health conference in 2007 and his travel costs were paid for by Alcoa of Australia, but he received no lecturing or other fee for giving this talk. Bill Musk has been paid by Pauline Pfizer Pharmaceuticals to give lectures on the epidemiology and the management of mesothelioma in Adelaide and Melbourne. Bill Musk, Nick de Klerk and Lin Fritschi are also investigators of the Healthwise programme of studies, which is funded by Alcoa of Australia. Michael Abramson, Geza Benke, Jisheng Cui, Martine Dennekamp and Anthony Del Monaco have no competing interests to declare.
Ethics approval This study was conducted with the approval of the Standing Committee on Ethics in Research Involving Humans, Monash University.
Provenance and peer review Not commissioned; externally peer reviewed.