CAUSE-SPECIFIC MORTALITY AND CANCER INCIDENCE AMONG EMPLOYEES EXPOSEDTO 2,3,7,8-TCDD AFTER A 1953 REACTOR ACCIDENT

Objective-To evaluate the long term health consequences of past occupa tional exposure to 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD). Methods -Cancer incidence and cause specific mortality were examined up to and including 1992 in a group of 243 men with external comparisons and in ternal dose-response analyses. Model based estimates of TCDD dose (exp ressed in mu g/kg body weight) were developed for all cohort members w ith an approach that incorporated detailed accounts of each employee's work activities, analyses of TCDD in blood lipid of 138 employees, an d internally derived estimates of elimination rates of TCDD. Results-T he estimated dose of TCDD for 135 men was greater than or equal to 0.1 mu g/kg body weight and for 69 men greater than or equal to 1 mu g/kg body weight. Increased cancer risk ratios were found with higher dose s of TCDD and longer interval since first exposure for all sites combi ned and digestive and respiratory cancers in particular. Within the hi gh dose group (greater than or equal to 1 mu g/kg body weight), total cancer mortality was increased greater than or equal to 20 years after first exposure (13 cases, standardised mortality ratio (SMR) 1.97, 95 % confidence interval (95% CI) 1.05-3.36) as was respiratory cancer (s ix cases, SMR 3.06; 95% CI 1.12-6.66). Among current cigarette smokers , 12 cancer deaths occurred in the high dose group (SMR 3.42, 95% CI 1 .77-5.97) compared with seven deaths at lower doses of TCDD (SMR 1.29, 95% CI 0.52-2.66). Regression analyses based on the Cox's proportiona l hazards model provided further evidence of a relation between cumula tive dose of TCDD and occurrence of both overall and digestive cancer. No evidence of an effect of TCDD on overall mortality or deaths due t o circulatory disease was found and no cases of non-Hodgkin's lymphoma or soft tissue sarcoma have been found to date. Conclusions-Our findi ngs are consistent with a carcinogenic effect induced by TCDD at doses greater than or equal to 1 mu g/kg body weight. With such a small coh ort, the risk estimates are not very stable and could be affected by s election and confounding.