Dioxins are highly toxic to foetuses and prenatal exposure leads to adverse health effects; however, the metabolic pathways involved in dioxin excretion are poorly understood. We determined the dynamics of maternal-to-foetal dioxin transfer during normal pregnancy and how foetuses eliminate polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and non-ortho polychlorinated biphenyls. Dioxin levels in maternal blood, cord blood, placenta, vernix caseosa, meconium, and amniotic fluid were analysed by high-resolution gas chromatography/mass spectrometry. The average levels of total dioxins, expressed as picograms of toxic equivalency quantity per gram of lipid and in parentheses, dioxin fraction, with maternal blood levels arbitrarily set as 100%, were as follows: maternal blood, 15.8 (100%); placenta, 12.9 (81.5%); cord blood, 5.9 (37.2%); vernix caseosa, 8.4 (53.2%); meconium, 2.9 (18.2%); and amniotic fluid, 1.5 (9.2%). Similar proportions were observed for each dioxin congener. Thus, the highest content of foetal dioxins was observed in the vernix caseosa, indicating that this is the major site of dioxin excretion in human foetuses.
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