A3.2.7 Metals


Metals are naturally occurring elements, which include cadmium, lead and copper. A heavy metal is a metallic element with a high density. Many heavy metals are toxic (although not all, for example, iron is essential for humans).

Heavy metal pollution can arise from many sources but most commonly arises from the purification of metals, such as the smelting of copper and the preparation of nuclear fuels. Electroplating is the primary source of chromium and cadmium.

Heavy metal pollutants can localize and lay dormant. Unlike organic pollutants, heavy metals do not decay and therefore pose a different kind of challenge for remediation. Currently, plants or microrganisms are tentatively used to remove some heavy metals such as mercury. Plants which exhibit hyper accumulation can be used to remove heavy metals from soils by concentrating them in their bio matter. Some treatment of mining tailings has occurred where the vegetation is then incinerated to recover the heavy metals.


Lead is used in the manufacture of lead-acid batteries, bullets and shot weight. It is also part of solder and radiation shields. It is a potent neurotoxin (acts specifically on nerve cells) and is able to accumulate in tissue over time. It is known to cause blood and brain disorders


Mercury and most of its compounds are extremely toxic. It can be inhaled and absorbed through the skin and mucous membranes. Mercury can cause both chronic and acute poisoning.

Fish and shellfish have a natural tendency to concentrate mercury in their bodies. Species that are higher up the food chain, such as sharks, swordfish and tuna contain higher concentrations of mercury than others. When this fish is consumed by a predator, the mercury level is accumulated.

Natural sources of mercury include volcanoes, which are responsible for approximately half of all atmospheric mercury emissions. Man-made sources of mercury include the production of gold, non-ferrous metals, cement and caustic soda.