Which metals can cross the placenta?

• A. Arsenic, Mercury, and Lead
• B. Arsenic only
• C. Mercury only
• D. Lead only

Answer: (A)

Transplacental transfer depends on the chemical form and properties of the metal, including size, lipophilicity, and the transport systems present at the placenta. Arsenic, in its inorganic forms, can cross the placental barrier and reach fetal tissues, contributing to potential growth and developmental effects. Mercury, especially methylmercury, crosses readily because it mimics amino acids and is transported by placental amino acid transporters, leading to fetal exposure that can affect neurodevelopment. Lead also crosses the placenta, partly via transferrin-mediated transport, allowing lead to reach fetal blood and tissues.

Because all three metals can cross the placenta, the option listing arsenic, mercury, and lead is the best choice. The other options omit metals that are known to cross placental transfer.