Study of cancer incidence among 6363 male workers in four Norwegian ferromanganese and silicomanganese producing plants

Objectives-Little has been known about the risk of cancer associated with o ccupational exposure to manganese. The objective of this study was therefor e to examine the associations between duration of specific work and cancer incidence among employees in four Norwegian ferromanganese and silicomangan ese producing plants. Methods-Among men first employed in 1933-91 and with at least 6 months in t hese plants, the incident cases of cancer during 1953-91 were obtained from The Cancer Registry of Norway. The numbers of various-cancers were compare d with expected figures calculated from age and calendar time specific rate s for Norwegian men during the same period. Internal comparisons of rates w ere performed urith Poisson regression analysis. The final cohort comprised 6363 men. Results-A total of 607 cases of cancer were observed against 596 cases expe cted (standardised incidence ratio (SIR) 1.02). Internal comparisons of rat es showed a positive trend between the rate of all cancers and duration of furnace work, A slightly weaker trend was also found for duration of blue c ollar non-furnace work when lags of 25 or 30 years were applied in the anna lyses. However, several results indicated that the incidence of all cancers among the non-furnace workers decreased during the period of active employ ment. Conclusions-Furnace and non-furnace workers may have exposures that increas e the incidence of several cancers. The low incidence of cancer among non-f urnace workers during the period of ongoing exposure cannot be explained. A s this study cannot identify any causal factors, the role of exposure to ma nganese remains unclear.