Mortality of workers employed in two asbestos cement manufacturing plants

Abstract

In a study of the mortality experience of 6931 employees of two New Orleans asbestos cement products manufacturing plants over 95% were traced. Chrysotile was the primary fibre used in both plants. Plant 1 also used small amounts of amosite and, later, crocidolite irregularly whereas plant 2 used crocidolite steadily in pipe production. Previously reported exposure concentration estimates were revised, based on additional air sampling data and re-evaluation of these data. Workers in the two plants had similar duration of employment (overall, a mean of 3.8 years) and estimated exposure concentration (a mean of 7.6 million particles per cubic foot (mppcf)). Mortality was similar for these plants and comparable with Louisiana rates for all causes combined, nonmalignant causes, and primary cancers of specified sites other than lung. Short term workers from both plants showed raised and similar risk of lung cancer, but risk among longer term workers differed--for example, for workers employed over one year there was no excess in plant 1 (16 observed, 17.2 expected) but a significant excess in plant 2 (52 observed, 28.9 expected, p less than 0.001). After excluding short term workers, risk of lung cancer in plant 2 showed a significant trend with estimated cumulative asbestos exposure; using a conversion of 1.4 fibres/ml = 1 mppcf, the slope of the line was 0.0076. The slope for plant 1 was 0.0003. Among all workers (the 6931, plus 167 early employees) ten mesotheliomas had occurred up to 1984: two from plant 1, eight from plant 2. In plant 2 a case-control analysis found a relation between risk of mesothelioma and duration of employment (p less than 0.01) and proportion of time spent in the pipe area (p less than 0.01), thus adding to the evidence of a greater risk of mesothelioma from crocidolite than chrysotile asbestos. A review of the mortality findings of eight cohorts of asbestos cement workers is presented.