Teratology of Heavy Metals: Mercury and Other Contaminants*

Abstract

Abstract Modern industrialization has introduced harmful metals into our environment, and there has been a good deal of speculation that heavy metals can cause teratogenesis. In fact many metals have been confirmed to have em‐bryotoxicity in experimental animals, but only a few elements (e.g., mercury, lead, etc.) are known to be human teratogens.Liquid metallic mercury is hardly absorbed from the gastrointestinal tract. Inorganic mercury is also poorly absorbed, i.e., around 2% of ingested mercuric chloride is absorbed. Uptake of inorganic mercury by the fetus is very low. An experiment using mice revealed that a significant proportion of mercury is blocked in the yolk sack. Among the organic mercury compounds, the most accumulated knowledge pertains to methylmercury compounds. Methyl‐mercury is efficiently absorbed through the intestinal tract and skin. It crosses the human placenta with infantile blood levels in excess of the mother's blood, giving rise to a higher risk for the fetus. Pathological features of children's brains affected by prenatal methylmercury exposure are the outcome of disturbances in the development of the brain; microcephaly, dilated lateral ventricles, as well as derangement in the fundamental structuring of gray matter as the result of abnormal neuronal migration. Degeneration of already formed nerve cells is involved in some cases.Lead has been shown to pass through the human placenta readily, and the concentration in the umbilical cord blood is 80‐90 % as high as that in the maternal blood. A large cohort study suggests that increased exposure to lead from the environment in the prenatal and early postnatal periods results in the deficit of mental development.Teratogenicity of many metal compounds such as aluminum, cadmium, chromium, indium, nickel, platinum, tellurium, thallium, ytterbium and zinc salts has been confirmed in experimental animals. Some metalloids (e.g., arsenic, selenium and lithium) appear to have teratogenic potential for humans.