Levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the serum of U.S. chemical workers exposed to dioxin contaminated products: Interim results

NIOSH is conducting a medical study to evaluate the current health status of 400 chemical workers who made products contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and an unexposed referent group matched for age, sex, race and neighborhood of residence. The workers are from two U. S. facilities which produced 2,4,5-trichlorophenol and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) between 1951 and 1972. As a measure of their exposure to 2,3,7,8-TCDD, serum from each worker and from a sample of referents was analyzed for the concentration of this isomer. In this preliminary report, we present the results of the analyses for 2,3,7,8-TCDD found in the serum of 46 study participants. In general, the mean of 8.2 parts per trillion (ppt) 2,3,7,8-TCDD found in the unexposed group is comparable to levels found in unexposed persons in industrialized nations. However, the mean level of 208.2 ppt found in the workers greatly exceeds background levels (p<.0001). The current levels for workers are related to the duration of employment in the production of substances contaminated with 2,3,7,8-TCDD (r=.816, p<.0001). Since all workers were last exposed prior to 1973, serum levels of 2,3,7,8-TCDD at termination of employment were estimated by assuming a 7 year half-life.