Skin exposure may represent a route of uptake for some organometallic compounds, especially those containing lead, but trace metals enter the human body primarily following oral or pulmonary exposure. The most hazardous volatile metal particles are those that are able to cross the pulmonary epithelium, although pulmonary uptake is significant only in highly polluted regions or in the case of heavy smoking. Some metals, such as cadmium, can also be absorbed through the olfactory epithelium and directly reach the central nervous system. However, for human populations in general, exposure to metals occurs mainly through food and drink. Toxic metals can be found in most soft tissues, especially the liver and kidneys, as well as in bones.
Placenta is another target tissue especially for lead, cadmium and mercury.
As routes of excretion include milk secretion, metals can be transferred to newborns via lactation. The adverse effects caused by metals vary with the dose and the time of exposure. Cancer has also been linked to metal exposure. Malignant changes caused by metals have been shown in rodents, but information pointing to the existence of a carcinogenic potential for metals in humans is limited. However, on the basis of results of epidemiological studies, the International Agency for Research on Cancer now recognizes the carcinogenic risk that some metals could pose to humans.