Polychlorinated dibenzodioxins and polychlorinated dibenzofurans

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (dioxins) are contaminants with long biological half-lives. The most toxic dioxin, 2,3,7,8-tetrachlorodibenzodioxin (TCDD), has a half-life in humans of 9 years. A tolerable daily intake (TDI) of 10 pg/kg body wt/day has been recommended, which was derived from steady-state concentrations of TCDD at the no-observed-adverse-effect level in animal studies. Intakes of dioxins by breast-fed babies can exceed the TDI by almost 20-fold. However, assuming a half-life of 9 years for all dioxins, it can be shown that the steady-state body burden is not increased by the short period of high intake during breast feeding, compared to that resulting from ingestion of the TDI daily from birth. Therefore, the TDI appears to accommodate the high intakes of dioxins by breast-fed babies. For dioxins with a significantly shorter half-life than TCDD, it can be shown that breast feeding will lead to higher body burdens in early life than would have been reached by ingestion of the TDI daily from birth. However, these peak body burdens will still be below the steady-state body burden achieved by ingestion of 10 pg TCDD/kg body wt/day from birth.