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The study comprises 7,410 male employees from the Norwegian primary aluminium industry, and presents overall mortality as well as cancer incidence. During the period 1953-79, 428 new cases of cancer were observed compared to the expected number of 412.2. The only statistically significant difference for the four investigated plants combined was cancer of the lung with 57 observed against 35.9 expected cases. The increased risk was almost solely confined to two subgroups in processing departments; workers with a short duration of employment and workers with a very long duration of employment in the older plants. These results were difficult to interpret because of the problems in selecting the appropriate reference population for estimation of expected number of cases of lung cancer. Furthermore, the individual occupational histories were incomplete and there was no information on smoking habits. In order to determine whether there is an excess risk for workers with long periods of employment in the newer plants, it is necessary to wait for another 10-20 years, when more conclusive data will become available.

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The predominant asbestos fibre type used in the production of asbestos cement is chrysotile. The use of asbestos in relation to fibre type in a Norwegian asbestos cement plant during 1942-80 was 91.7% chrysotile, 3.1% amosite, 4.1% crocidolite, and 1.1% anthophyllite respectively. Electron microscopy and x ray microanalysis of lung tissue samples of asbestos cement workers who had died of malignant pleural mesothelioma or bronchogenic carcinoma showed a completely inverse ratio with regard to fibre type. The percentage of chrysotile asbestos in lung tissue varied between 0% and 9% whereas the corresponding numbers for the amphiboles were 76% and 99%. These differences are discussed with respect to the behaviour of different fibre types in the human body and to the occurrence of malignant mesothelioma in this asbestos cement factory.

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