MODELING OF 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN LEVELS IN A COHORT OFWORKERS WITH EXPOSURE TO PHENOXY HERBICIDES AND CHLOROPHENOLS

Several cohort studies of herbicide manufacturing workers have been co nducted over the last years. Most of these studies used simple proxies of exposure in the analysis such as a crude grouping in exposure cate gories based on job titles, presence in certain production areas over a period of time or during an accident, and duration of expo sure. Cur rent serum 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) levels available for a subset of workers can be used to back-extrapolate TCDD levels a t the end of exposure using first order kinetic models, and relate TCD D levels to job history using regression models. The regression model obtained can be used to estimate TCDD levels for all cohort members. I n this paper, the effect of changes in model assumptions on estimated TCDD levels is explored. TCDD levels are back-extrapolated assuming di fferent values for TCDD half-life. A range of regression models with d ifferent sets of exposure determinants is used to relate back-extrapol ated TCDD levels to determinants of exposure. These models were used t o predict TCDD levels in the epidemiological analysis of data from a D utch cohort study. The results show that the predicted serum TCDD leve l is strongly dependent on the assumed half-life. However, the ranking of all individuals on the exposure axis (from low to high) is not aff ected by changes in the half-life. Predicted serum TCDD levels seem no t sensitive to changes in assumption regarding TCDD half-life. Predict ed TCDD levels were positively associated with increased (cause specif ic) mortality. (C) 1998 Elsevier Science Ltd. All rights reserved.