Teratogenicity and embryotoxicity of metals in humans and experimental animals

Unequivocal evidence indicates that methylmercury is teratogenic for human embryos or fetuses. Limited evidence suggests that exposures of pregnant wo men to Ni, As, or Pb compounds can induce pregnancy complications and adver sely affect the infants. Teratogenesis bioassays in rodents (hamsters, mice , or rats) have yielded positive results for compounds of Al, As, Bo, Cd, C o, Cr, Cu, Ga, Hg, Li, Mn, Ni, Pb, Se, U, V, and Zn, producing: fetal and e arly postnatal deaths, as well as malformations (e.g., exencephaly, eye def ects, cleft palace, skeletal anomalies). Exposures to Cd, Co, Cu, CH3Hg, Li , Ni, Pb, and Zn during embryogenesis have been reported to cause developme ntal malformations of the South African frog, Xenopus laevis (e.g., bent ta il, craniofacial deformity, ocular abnormalities, intestinal malrotation, c ardiac anomalies). Most of the investigations in frogs have followed the FE TAX protocol, a standard bioassay system for identification of chemical ter atogens. Studying the ligand interactions and biochemical effects of metals during embryogenesis in Xenopus laevis provides a powerful approach to elu cidate the specific mechanisms and molecular targets of teratogenesis and e mbryotoxicity.