Developmental Disabilities Following Prenatal Exposure to Methyl Mercury from Maternal Fish Consumption: A Review of the Evidence

Abstract

Mercury is ubiquitous in the environment, and the amount an individual comes in contact with it is increasing. The organic form of methyl mercury (MeHg) is very toxic to the central nervous system (CNS). All fish contain small amounts of MeHg, and everyone who consumes fish or seafood is exposed to it. Once inside the body, MeHg readily crosses the placenta and the blood–brain barrier and enters the CNS. MeHg poisoning episodes have clearly demonstrated that the developing fetal brain is especially sensitive, and it can be seriously impaired, even when the mother has no symptoms. The events in Japan confirm that consuming fish that is heavily contaminated with MeHg can damage the developing CNS. However, interpreting the Japanese experience is complicated by the very high exposures and the presence of other toxins in the factory waste. Studies of poisoning in Iraq suggest that a level of prenatal exposure of around 10 ppm measured in maternal hair might adversely affect the developing fetus. Individuals who consume fish with only background levels of MeHg can achieve a hair level of 10 ppm or greater. However, there are no reported cases of mild disability after prenatal MeHg exposure and no reports of poisoning from fish consumption outside of Japan.