Mortality and cancer morbidity in workers from an aluminium smelter with prebaked carbon anodes--Part II: Cancer morbidity.

OBJECTIVE: To investigate associations between cancer incidence and exposure to coal tar pitch volatiles, asbestos, pot emissions (fluorides, sulphur dioxide), heat stress, and magnetic fields in workers from a Norwegian aluminium smelter that operated from 1914 to 1975.
METHODS: Cancer incidence between 1953 and 1991 was recorded in a cohort of 1137 men hired between 1922 and 1975. The expected number of cancer cases was calculated from incidence rates in Norwegian men. A job exposure matrix with semiquantitative exposure estimates was used to investigate associations between cumulative exposure estimates was used to investigate associations between cumulative exposure and cancer incidence through exploring temporal relations by considering exposures only within specific time windows.
RESULTS: A significant excess of cancer cases, 90 observed v 59.0 expected, was found in workers who had been employed for less than three years. No such excess was found in men with at least three years' employment, with 120 cases observed v 129.7 expected. In this subcohort an association was found between the incidence of bladder cancer and exposure to coal tar pitch volatiles 40 years or more before each person-year under observation, and between incidence of lung cancer and tar exposure 35-50 years before observation. An association was also found between incidence of kidney cancer and exposure to heat stress 20-35 years before observation.
CONCLUSIONS: The results support previous findings that exposure to coal tar pitch volatiles in the aluminium industry has been associated with increased risk of bladder and lung cancer. They also add information about temporal relations, suggesting that exposure to tar in this smelter has acted on an early stage in the development of these cancers, followed by a latency period of 30-40 years.