A toxic heavy metal is any relatively dense metal or metalloid that is noted for its potential toxicity, especially in environmental contexts. The term has particular application to cadmium, mercury, lead, and arsenic, all of which appear in the World Health Organization’s list of 10 chemicals of major public concern. Other examples include manganese, chromium, cobalt, nickel, copper, zinc, selenium, silver, antimony, and thallium.
Toxic heavy metals are found naturally in the earth and become concentrated as a result of human-caused activities. They enter plant, animal, and human tissues via inhalation, diet, and manual handling, and can bind to and interfere with the functioning of vital cellular components.
The toxic effects of arsenic, mercury, and lead were known to the ancients, but methodical studies of the toxicity of some heavy metals appear to date from only 1868. In humans, heavy metal poisoning is generally treated by the administration of chelating agents. Some elements regarded as toxic heavy metals are essential, in small quantities, for human health.
Further Reading:
6 Essential Oils for Detoxing Heavy Metals