Mercury (Hg), a heavy metal with widespread distribution and extensive human exposure through food consumption, has been implicated in numerous adverse health effects. Developing fetuses are particularly vulnerable due to the efficient transfer of neurotoxic methylmercury (MeHg) across the placental and blood-brain barriers.
This study involved 15 mother-infant pairs in Hong Kong to investigate placental Hg transfer and dietary influences on the fetal exposure. For each pair, tissue samples were collected from three sites of umbilical cord from fetus to placenta and six random regions of placental basal and chorionic plates for various analyses, and alongside maternal and cord blood for complete blood count. Total Hg (THg) and MeHg levels were quantified by cold vapour atomic fluorescence spectrometer. Stable isotopes ratios of nitrogen and carbon in tissues were measured via continuous flow-isotope ratio mass spectrometry to infer maternal dietary sources.
Isotopic analysis revealed that umbilical cord THg and MeHg levels were strongly associated with cord d¹⁵N (adjusted R² = 0.58, p < 0.0001). Each 1‰ increase in d¹⁵N, equivalent to ~25% of a trophic level elevation, was linked to an average of 20.4 ng/g increase in THg and 13.3 ng/g increase in MeHg. Cord d¹³C exhibited a significant positive correlation with THg (adjusted R² = 0.18, p < 0.01), reflecting Hg inputs from d¹³C-enriched diets (e.g., seafoods). Placental tissue comparisons further demonstrated a 15% reduction in THg (p < 0.001) with a 32% reduction in MeHg (p < 0.001) from the maternal-facing basal plate to the fetal-facing chorionic plate, may underscore partial but incomplete placental filtration of Hg species in the Hg transfer. These findings highlight the critical roles of maternal diet and haematological health in shaping fetal Hg burdens, and potentially its risk. Public health strategies should integrate dietary guidance for pregnant women.

mercury,methylmercury,maternal and fetal health,stable isotopes analysis