Abstract:Mercury (Hg), a heavy metal with widespread distribution and extensive human exposure through food consumption. 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 CVAFS. Stable isotopes ratios of nitrogen and carbon were measured via CF-IRMS. Isotopic analysis revealed that cord THg and MeHg levels were strongly associated with cord d15N (adjusted R² = 0.58, p < 0.0001). Each 1″° increase in d15N, 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. 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. Furthermore, markers of microcytic anaemia (MCH < 27 pg; MCV < 80 fL) were associated with increased placental THg, indicating that association of low haemoglobin production with the fetal Hg exposure. These findings highlight the roles of maternal diet and health in shaping fetal Hg burdens. Public health strategies should integrate dietary guidance for pregnant women, particularly in coastal regions with high Hg exposure, and RBC indices to identify high risk pregnancies.
Keywords: Global Health Nutrition, Human reproductive health, fetal health, mercury toxicity, stable isotopes tracing
