Metals, objects made from metal, and chemical compounds containing metal are pervasive in the home, workplace, and environment. Although metals play an essential role in modern human society, there are many instances where they occur as unneeded and harmful contaminants. Heavy metals such as mercury, cadmium, lead, uranium, chromium, manganese, nickel, thallium, and bismuth are all industrially useful, but they are also potentially harmful at high concentrations in the environment or when found in food or drinking water. Environmental contamination with heavy metals can result from many activities including mining, large-scale combustion of coal in heating or power plants, mineral and metal processing, and use of fungicides and pesticides.

The metal mercury (Hg), a useful component of many products including thermometers, pesticides, drugs, paints, and batteries, is unusual in that it is a liquid at ordinary temperatures. It forms a variety of useful salts...