Teratology of Heavy Metals: Mercury and Other Contaminants*

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.

Embryotoxic and Teratogenic Effects of Nickel in Swiss Albino Mice during Organogenetic Period

“…Exposure to methyl mercury leads to disturbances in the development of the brain, which included microcephaly caused due to dilation of lateral ventricles and derangement in the fundamental structure of gray matter as a result of abnormal neuronal migration [30]. Enlargement of cerebral ventricles (hydrocephaly) have also been reported in various metals like gold [31], chromium [32], and mercury [33].…”

Birth defects in Iraq and the plausibility of environmental exposure: A review

“…The possibility of exposure to other specific local risk or causal factors particularly heavy metals needs to be investigated. Animal teratogenesis by a variety of heavy metals and human teratogenesis by at least lead and mercury are long established [ 55 ]. In Iraq, several studies described lead exposure and toxicity to lead in Baghdad [ 56 , 57 ] and Al-Anbar governorates [ 58 ].…”

Teratogenicity of depleted uranium aerosols: A review from an epidemiological perspective

“…First, elegant studies of other heavy metals suggest study designs that may be emulated; second, observed associations can inform and contribute to the choice of outcomes for DU studies since various heavy metals may have similar modes of action. Accumulated knowledge of heavy metal teratology is quite extensive; animal teratogenesis by a variety of heavy metals, and human teratogenesis by, at minimum, lead and mercury, are long established [34]. A 1996 study of human anencephaly vis a vis parental and in utero ambient exposure to lead, mercury and vanadium is exemplary.…”