Update of the mortality study of workers exposed to polychlorinated biphenyls (PCBs) in two Italian capacitor manufacturing plants

Background: PCB carcinogenicity to humans is still controversial. Cohort mortality studies in PCB-exposed workers reported elevated risks for the following causes of death: liver, stomach, digestive, brain, prostate cancers and non-Hodgkin lymphoma. Objectives: The purpose of this study was to update as of December 2006 the mortality experience of two Italian cohorts of workers employed in the manufacture of capacitors impregnated with PCBs. Methods: Age-gender-and calendar period adjusted Standardized Mortality Ratios (SMRs) and 95% Confidence Intervals (CI) were calculated using regional rates. Analyses by duration of employment and time since first employment were performed. Results: Vital status was ascertained for 98.9% of the study subjects. Mortality from biliary tract cancer among males (SMR 3.91; 95%CI 1.47-10.41), digestive cancer "not otherwise specified" in the whole cohort (SMR 2.54; 95%CI 1.21-5.34), and brain cancer in Plant 1 (SMR 2.13; 95%CI 1.02-4.48), were significantly increased. Increased risks were also observed for Hodgkin's and non-Hodgkin lymphoma. No linear associations between mortality and duration of employment or latency were observed for these cancers. Mortality from stomach cancer did not differ from expectation in the whole cohort, however an increasing risk with increasing duration of employment was detected (p for trend=0.02). Conclusions: The current update suggests possibly increased cancer risks in PCB-exposed workers, affecting in particular the digestive system, brain, and lymphohemopoietic tissue. However the limited sample size, the lack of clear trends with duration of employment or with latency period, preclude to derive definite conclusions about PCB exposure and the increased cancer risks.