Predicted concentrations of polychlorinated dibenzo-p-dioxins and furans in fat tissue due to chlorophenate exposure in B.C. sawmills

Chlorophenols were used to prevent sapstain fungal growth on lumber in sawmills located in Canada, the United States Scandinavia, and elsewhere, from the 1940s to the late 1980s. Elevated levels of chlorophenols have been measured in the urine of sawmill workers particularly those with dermal exposure. Since polychlorinated dibenzodioxins (PCDDs) and furans (PCDFs) are contaminants created in the manufacture of chlorophenols, it is expected that sawmill workers were exposed. PCDD/Fs have half-lives on the order of years and accumulate in adipose tissue. Biological monitoring is not easily carried out due to its invasive nature and cost, consequently little information exists on PCDD/F levels in sawmill workers. In a cohort of Canadian sawmill workers assembled for a cancer incidence and mortality study, we estimated the adipose tissue concentrations of PCDD/F compounds, using a singlecompartment pharmacokinetic model. Estimates of dermal and inhalation exposure to chlorophenols throughout the working lives of the sawmill workers were combined with PCDD/F contamination levels, half-lives, and absorption efficiencies to estimate tissue concentrations. Each variable in the model was assigned a distribution based on literaturereported data, as well as information about the sawmill cohort. The predicted distributions of PCDD/F concentrations were then estimated using 5,000-run Monte Carlo analyses. Predicted median adipose tissue concentrations of all dioxins and tetra- and penta-chlorinated furans among the sawmill workers were similar to background levels in unexposed residents of the same region, though about 10 to 30% of sawmill workers were estimated to have elevated levels of these congeners. Median levels of hexa-, hepta-, and octa-chlorinated furans were predicted to be 2 to 15 times background levels. Sensitivity analyses indicate that the variability of the model predictions was most influenced by estimates of PCDD/F skin absorption efficiency, duration of employment at the sawmill, and levels of PCDD/F in chlorophenols.Medicine, Faculty ofPopulation and Public Health (SPPH), School ofGraduat