Heavy metals are individual metals and metal compounds that can impact human health. These are all naturally occurring substances which are often present in the environment at low levels. In larger amounts, they can be dangerous. Generally, humans are exposed to these metals by ingestion (drinking or eating) or inhalation (breathing).Working in or living near an industrial site which utilizes these metals and their compounds increases ones risk of exposure, as does living near a site where these metals have been improperly disposed. Subsistence lifestyles can also impose higher risks of exposure and health impacts because of hunting and gathering activities.
Common sources of these heavy metals are from mining and industrial wastes; vehicle emissions; lead-acid batteries; fertilisers; paints; treated woods; and aging water supply infrastructure. In children’s toys Arsenic, cadmium and lead may be present at levels that exceed regulatory standards. In toys as a stabilizer, color enhancer, or anti-corrosive agent lead can be used.
Over the past few decades, there has been growing concern about human reproductive disruption by xenobiotics including drugs, occupational and environmental exposures. Environmental toxicologist studied the effect of environmental toxicants on the different components of the environment and the health of all organisms.
Lead is one of the most toxic environmental and industrial pollutants. Its industrial applications were based on its unique chemical and physical properties. Lead is a ubiquitous toxic heavy metal and unlike organic compounds, it is not biodegradable and has a very long biological half life. In spite of many studies, the mechanism of its toxicity has not yet well interpreted and in contrast to other metals, there is no effective therapy has been developed for its poisoning.
Humans have been mining and using this heavy metal from thousands of years, poisoning themselves in the process. Although lead poisoning is one of the most hazardous environmental problem. The modern understanding of the small amount of lead, which is necessary to cause harm, did not come until the latter half of the 20th century. No safe threshold for lead exposure has been discovered yet. There is no known amount of lead which is too small to cause the body impairment.
Lead is using in the manufacture of other lead salts, as the mordant in dyes, coating for metals, drier in paints, varnishes and pigment inks and as a colorant in hair dyes. It came into use very early in the history of civilization and its toxic effects were discovered at early age of civilization.