Prenatal and developmental toxicology of arsenicals.

A variety of species, including the human, have been shown to be susceptible to the embryotoxic effects of inorganic arsenic. Malformations of the axial skeleton, neurocranium, viscerocranium, eyes, and genitourinary systems as well as prenatal death followed a bolus dose of trivalent or pentavalent inorganic arsenic. Trivalent arsenic was more teratogenic than pentavalent arsenic; in contrast, the methylated metabolites of arsenic possessed only limited teratogenic activity. Administration of inorganic arsenic to mammals results in concentration of arsenic within the placenta and small amounts are deposited within the embryo. Studies concerning the pathogenesis of arsenic-induced axial skeletal lesions revealed early failure of neural fold elevation and a subsequent, persistent failure of closure of the neural tube. Physical factors, drugs and heavy metals may modify the response to a teratogenic dose of inorganic arsenic. Medical problems associated with industrial or agricultural arsenicalism are most often typified by chronic exposure; future studies should emphasize those routes of administration and types of exposure that are characteristic of arsenic intoxication.