Mortality study of workers at a patent fuel plant

This report describes the mortality, over a 17-year period from 1 January 1967 until 31 December 1983 among workers employed at a patent fuel plant in South Wales. While employed there, men were exposed variously to pitch, coal dust, and to the fumes and by-products from coal carbonisation. The main purpose of the study was to determine the association, if any, between occupation at the works and subsequent mortality.The study was designed to include all male industrial workers employed at the works on 1 January 1967. Staff at the plant identified 620 such men from personnel records and were confident that the study group had been identified completely.Occupational histories of work at the plant up to January 1976 were also obtained, primarily from works personnel records. In liaison with staff from the works, the many job names with associated place of work were combined into 10 occupational groups including briquetting, carbonisation, by-products, non-direct process jobs and general work. Missing dates of job changes caused problems which were resolved only partially.Many (477) of the men studied had attended a survey of respiratory symptoms carried out by this Institute at the plant in November 1968. A questionnaire of respiratory symptoms had been administered, and details of smoking habits and of previous experience in mining had been recorded. These data were also used in the current project.Eleven men were excluded from analyses because of missing data. It was confirmed that 479 others were still alive on 31 December 1983, while death certificates were obtained for all of the remaining 130 men who had died during the 17-year study period. The 130 deaths observed was slightly greater than the number of 126 expected based on the experience of all men in Wales at that time who were of similar age to the 609 studied. This finding contrasts with the experience of industrial workers generally, whose death rates are lower than the general population of the same age. (Compared with the general population, men must be relatively fit to secure employment initially as industrial workers, and to stay in employment thereafter until retirement age.)Analyses of cause-specific mortality showed that there were more deaths than expected from cancers in general, 38 observed compared with 30.2 expected, though excess cancer mortality was not found in the recent years of the follow-up (1980-83). The specific sites involved were lung (17 observed, 11.7 expected), stomach (6 observed, 3.7 expected), bladder (3 observed, 1.3 expected) and prostate (2 observed and 1.1 expected). There were no deaths from cancer of the kidney.The risks of lung cancer were higher in smokers than in non-smokers. However, smoking is not likely to be an explanation of the excess lung cancer deaths: the expected deaths of 11.7 take account of the smoking habits of men in the general population, and the available data give no pointers that the men in this study were heavier smokers than are other working men.Ten of the lung cancer deaths occurred among men between 15 and 20 years since first joining the patent fuel plant, compared with 3.2 expected. This finding is consistent with a latent period for development of lung cancer related to occupation at the works. Associations between lung cancer mortality and previous work in the plant were not established clearly, but results pointed to work in by-products and carbonisation rather than to the briquetting plant.The position with cancers of other sites is less clear, partly because the numbers of deaths were small. The only main finding was that there was no evidence that men who died of cancer of the bladder or of the prostate had previously worked in the main pitch-handling jobs. Nevertheless, in view also of the evidence of other studies linking bladder cancer with coal tar products, we think that the bladder cancer excess in the present study may also be work-related. It is unclear to what extent work at the factory may have contributed to the excess of stomach cancer.An excess of ischaemic heart disease was found among younger men while older men showed fewer deaths than expected from this cause. A similar pattern has been found in other studies of coke workers and related processes. The consistency of the finding suggests that the effect may be work-related. However, a review of possible agents at the plant failed to show any source of exposure which would explain the excess. We think that further research is needed, to identify if this is a characteristic of younger industrial workers generally, and to clarify the possible role of other work-related factors such as temperature and patterns of shift work.Symptoms of chronic bronchitis were not closely associated with a history of work at the plant, whilst there was a strong association with previous work as a coalminer. Deaths from bronchitis and emphysema (10 deaths compared to 7.2 expected), and from pneumonia (9 observed, 4.8 expected), were in excess, and again ex-miners were at clearly higher risk. It was impossible to determine to what extent, if any, exposure in dusty jobs at the smokeless fuel works was a further contributory cause. We think that ill-health in ex-miners was the main cause of excess mortality from non-malignant respiratory causes in the workforce. However, the excess should not be interpreted as a measure of the hazards of coalmining, since the ex-miners employed at the patent fuel plant were almost certainly an unrepresentative group.Interpretation of these results was complicated by the small size of the study group, by complex health-related influences on employment at the factory and on job changes within it and by the absence of environmental measures of particular hazards; and despite the use of powerful statistical methods, few of the findings were statistically significant. Nevertheless, in the context of other findings on work and health, some firm conclusions can be drawn. The results strongly suggest that men at the factory are exposed to work-related cancer risks, particularly of the lung and probably of bladder also, and may further be at risk of ischaemic heart disease. It seems however that excess of deaths from non-malignant respiratory illness was largely due to the employment of ex-miners with untypically poor health.