Partition of metals in the maternal/fetal unit and lead-associated decreases of fetal iron and manganese: an observational biomonitoring approach

To systematically study the partition of environmental metals including lead, mercury, and cadmium and essential minerals such as iron, manganese, copper, and zinc in the maternal/fetal unit of healthy pregnant women, we analyzed blood and umbilical cord blood samples of 50 healthy mother/child pairs using a biomonitoring approach. The levels of essential minerals in healthy pregnant women were significantly different from those of the general population. The partition of essential minerals and environmental metals and their associations between maternal and umbilical cord blood were metal-specific. Lead entered the fetal environment nearly unaffected. The median fetal level was only 10 % lower than the corresponding maternal concentration (10.3 vs. 11.5 mu g/l, P = 0.0038). Mercury accumulated in the fetal unit resulting in more than a threefold increase in fetal compared to maternal exposure (1.48 vs. 0.44 mu g/l, P < 0.0001). In contrast, placental transfer of Cd was limited, and median fetal exposure was < 0.1 mu g/L. We finally used the data to assess the influence of exposures to environmental metals on fetal homeostasis of essential minerals because environmental metals such as lead are capable of interfering with normal cellular functions of essential minerals by mimicking their pathways. A subtle but systematic and dose-dependent effect of environmental exposure to lead on fetal homeostasis of manganese and iron in terms of reducing their concentrations in the fetal unit was found (P a parts per thousand currency sign 0.039). The observed associations remained unaffected in the presence of mercury and cadmium. The results illustrate the need to establish specific normative levels of essential minerals in pregnant women. Additionally, the study provides initial insights into the mode-of-action of lead in the fetus at current environmental exposures.