Metal ions affecting reproduction and development.

Many metal ions (lead, mercury, arsenic, cadmium, chromium, nickel, vanadium, copper, lithium) exert a wide variety of adverse effects on reproduction and development, including influence on male and female subfertility or fertility, abortions, malformations, birth defects, and effects on the central nervous system. The effects produced by metal ions depend on several factors, such as timing and duration of exposure, their distribution and accumulation in various organs (e.g., the nervous system), and on the interference with specific developmental processes. Neonatal and early postnatal periods are lifespan segments during which sensitivity to metals is high; e.g., lead toxicity on the developing organism is paradigmatic of related well known and still open questions. In more recent decades, important mechanisms of action have been suggested: the endocrine disruption via impact of metal ions on reproductive hormones and the oxidative stress. While experimental data provide clear evidence of effects of many metals, human data are scant and traditionally limited to high levels of a few metal ions, like lead on male fertility. Less documented are reproductive effects for mercury, manganese, chromium, nickel, and arsenic for the same gender. More complex is the demonstration of effects on female reproduction and on pregnancy. The action of lead, arsenic, cadmium, chromium, and mercury may in fact be relevant in several stages, beginning in fetal life, during early development or maturity, and is characterized by subfertility, infertility, intrauterine growth retardation, spontaneous abortions, malformations, birth defects, postnatal death, learning and behavior deficits, and premature aging. Also, for females the evidences of specific aspects such as fertility or abortions are usually higher and clearer from animal experiments than from human studies.