Title: Cancer Mortality in Workers Exposed to Tetra chloro Dibenzo Dioxin
Authors: Marilyn Fingerhut, William Halperin, David Marlow et.al
Study name: Retrospective Cohort study of Mortality done by NIOSH
Methodology : In 1978 NIOSH conducted a retrospective cohort study of mortality among the 5172 male workers at 12 plants in the U.S.A. that produced chemicals contaminated with TCDD between 1942 and 1984.They also made a high exposure subcohort of 1520 wo rkers with 1 yr of exposure and 20 yrs of latency.TCDD was generated as a contaminant in the production of trichlorophenol, defoliants like Agent Orange, herbicides, insecticides, and bactericides. Occupational exposure was documented by reviewing job descriptions, measuring TCDD levels in serum from a sample of 253 workers as adjusted for lipids and causes of death from death certificates. Life table analysis was used to evaluate mortality in the c ohort. SMRs were computed after sratification to adjust for the age, race and year of death.The U.S. population was used as a reference group. Duration of exposure was defined as the number of yrs the worker was employed in process involving TCDD contami nation and the duration of employment was defined as the number of yrs the that each worker was employed at a study plant.
Results, Conclusions or summations : The mean serum TCDD level as adjusted for lipids in the sample of 253 workers from 2 plants was 233 pg per gm of lipids as compared to 7 pg in unexposed persons.
Overall mortality for all causes of death was similar to national rates in the U.S. Mortality from heart disease was also similar to national rates.
Mortality from all cancers combined was slightly (abt 15%) but significantly increased but was more pronounced in the high exposure subcohort. (abt 46%)
Mortality from soft tissue sarcoma and cancers of the respiratory tract were nonsignificantly increased in cohort but significantly increased in the high exposure subcohort(abt 42% increase). After adjusting to smoking prevalence the expected number of d eaths due to lung cancer increased by 5% in cohort and by 1% in subcohort.
SMRs for other cancers like Hodgkins disease, Non Hodgkins lymphoma, stomach cancer, nasal cancer and liver cancer were nonsignificantly increased in cohort. SMRs were nonsignificantly higher for Hodgkins disease and stomach cancer and lower for Non Hodg kins lymphoma and liver cancer in high exposure subcohort group.
Anything else of major interest: The difficulties of evaluating soft tissue sarcomas in a cohort study of mortality included variability in pathological diagnosis and misclassification on death certificates. Excess mortality from all cancers combined, can cers of the respiratory tract, and soft tissue sarcoma may result from exposure to TCDD although we cannot exclude the possible contribution of factors such as smoking and occupational exposure to other chemicals.