Placental transfer efficiencies of multiple metals: Patterns, and influence factors

Environmental exposure to both toxic heavy metals and essential trace elements during pregnancy can influence fetal development through transplacental transfer. However, comprehensive knowledge of placental transfer efficiency (PTE) across a broad spectrum of metals remains limited. In this study, we quantified multiple metals in 228 paired maternal and umbilical cord blood samples and calculated their placental transfer efficiencies. Based on median PTE values, metals were categorized into four groups: poorly transferred (cadmium (Cd), 40 %; copper (Cu), 44 %; zinc (Zn), 26 %), partially transferred (lead (Pb), 69 %; strontium (Sr), 79 %), efficiently transferred (cobalt (Co), 102 %; gallium (Ga), 106 %; nickel (Ni), 99 %), and highly transferred with fetal accumulation (mercury (Hg), 148 %; manganese (Mn), 210 %; rubidium (Rb), 117 %). Despite variability among metals, the major exhibited an inverse association between maternal concentration and PTE. Most metals, such as Cd, Co, Cu, Mn, Pb, Rb and Zn generally display an overall pattern indicative of passive transplacental transport. These findings enhance understanding of fetal metal exposure risks and offer new insights into placental transport mechanisms, with important implications for risk assessment and early-life intervention strategies during preconception and pregnancy.