Toxicity, mutagenicity and teratogenicity of lead

Environmental contamination by lead has greatly increased as more and more lead is used for petrol (gasoline) and in various industrial products, although severe cases of lead intoxication, as often seen in former times, have become rare owing to better health care. These facts have drawn attention to effects of lead which may arise, possibly without a threshold, at low exposure levels. Among the classical manifestations of lead intoxication are, anemia, gastro-intestinal, renal and nervous symptoms. Those in the nervous system and perhaps also in the kidney may have consequences even at subclinical levels of lead exposure. Thus, the possibility that such exposure may cause mental alterations in children, induced late renal damage or affect nerve conduction is now much debated. The mechanisms of action of lead on the developing central nervous system is still uncertain. They may be related to a composition between lead and calcium on the synaptosomal level. Among the typical stochastic risks, tumors have been found in lead-intoxicated rodents, but do not seem to occur in man, and the situation with respect to genetic risks is not entirely clear. Certain effects of lead on genetic material have been observed in simple organisms, and it appears that lead exposure in vivo or in vitro can induce light chromosomal aberrations such as gaps and fragments. Under conditions of calcium deficiency, severe aberrations such as dicentrics may also arise, but the data on man are controversial because lead is almost never the only potentially mutagenic agent to which people are exposed in an industrial environment. Nevertheless, the efficiency of lead in causing such aberrations appears low compared with that of other mutagenic agents so that genetic effects of lead do not appear of primary concern for human health. Lead can prevent implantation of the embryo, delay its growth during later stages of pregnancy and, when injected during organogenesis particularly under conditions of calcium deficiency, cause malformations. The risks to the developing human organism are difficult to evaluate owing to the large differences in lead metabolism between man and rodent, so studies on species resembling man are desirable.