Mortality of workers exposed to polychlorinated biphenyls--an update.

A retrospective cohort mortality study of workers exposed to polychlorinated biphenyls (PCBs) in two plants manufacturing electrical capacitors was reported in 1981. The study was conducted primarily to examine the risk of cancer mortality associated with exposure to PCBs. Based on animal data, liver cancer was the disease of most interest. Due to the small number of deaths and a relatively short observation period, the study was considered inconclusive. This study has been updated by adding 7 yr of observation. The number of deaths in the study cohort has increased from 163 to 295. Mortality from all causes was found to be lower than expected (295 observed vs. 318 expected deaths) as well as mortality from all cancers (62 observed vs. 80 expected deaths). A statistically significant excess in deaths was observed in the disease category that includes cancer of the liver (primary and unspecified), gall bladder, and biliary tract (5 observed vs. 1.9 expected; p less than .05). Most of this excess was observed in women employed in one plant. Due to the small number of deaths and the variability of specific cause of death within this category, it remains difficult to interpret these findings in regard to PCB exposure.