To clarify the normal metabolism of mercurials in the human feto‐placental system, organic (or methyl) mercury and inorganic mercury were measured in maternal blood (MB), umbilical cord blood (UB), and chorionic tissues of the placenta (PC) and its blood vessels (PV), obtained from pregnant women just after delivery, as well as in fetal liver and fetal brain from induced abortion cases. Organic mercury was commonly detected in MB, UB, PC and PV, with slightly more elevated values in UB and PC than in MB, whereas inorganic mercury was detected in PC and PV, but not in MB and UB. In the fetal liver, 27–60% of mercury was in the form of inorganic mercury, whilst in four of five fetal brain samples, inorganic mercury was not detected. Additionally, fetal liver demethylation activity was studied in vitro. Incubation of methyl mercury with chopped fetal liver tissue for 24 h resulted in demethylation of approximately 1% of the methyl mercury.
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