Mortality study of workers employed at organochlorine pesticide manufacturing plants

A retrospective cohort study was conducted to examine the mortality of workers employed in the manufacture of the chlorinated hydrocarbon pesticides, chlordane, heptachlor, dichloro-diphenyl-trichloro-ethane (DDT) and aldrin/dieldrin/endrin. Four manufacturing plants were selected for study, and each cohort included all workers employed for at least six months prior to January 1964. The entire study group totaled approximately 2,100 individuals. Vital status ascertainment for these cohorts ranged from 90 to 97% complete; the cut-off date for follow-up was 31 December 1976. In general there were too few deaths in this study on which to draw any meaningful conclusions. The standardized mortality ratio (SMR) for all causes in each cohort was below the expected level (100) and ranged from 66 to 82, probably a reflection of the "healthy worker effect." For "all malignant neoplasms" the SMRs ranged from 68 to 91 and for respiratory cancer from 55 to 132. In the aldrin/dieldrin/endrin cohort observed deaths due to pneumonia and "other respiratory diseases" were significantly above the expected number of deaths. For several other specific cancer sites (stomach in plant 1, esophagus, rectum, liver and lymphatic/hematopoietic system in plant 3), the observed deaths were more than the expected number and should be examined in more detail. It is recommended that these cohorts be followed for several more years and the mortality patterns be reexamined.