Metal poisoning

Metal toxicity or metal poisoning is the toxic effect of certain metals in certain forms and doses on life. Some metals are toxic when they form poisonous soluble compounds. Certain metals have no biological role, i.e. are not essential minerals, or are toxic when in a certain form. In the case of lead, any measurable amount may have negative health effects. There is a popular misconception that only heavy metals can be toxic, but lighter metals such as beryllium and lithium can be toxic too. Not all heavy metals are particularly toxic, and some are essential, such as iron. The definition may also include trace elements when abnormally high doses may be toxic. An option for treatment of metal poisoning may be chelation therapy, a technique involving the administration of chelation agents to remove metals from the body.

Toxic metals sometimes imitate the action of an essential element, interfering with the metabolic processes resulting in illness. Many metals, particularly heavy metals are toxic, but some are essential, and some, such as bismuth, have a low toxicity. Metals in an oxidation state abnormal to the body may also become toxic: chromium(III) is an essential trace element, but chromium(VI) is a carcinogen.

Only soluble metal-containing compounds are toxic. Soluble metals are called coordination complexes, which consist of a metal ion surrounded by ligands. Ligands can range from water in metal aquo complexes to methyl groups as in tetraethyl lead. Usually metal complexes consist of a mixture of ligands.

Toxic metal complexes can be detoxified by conversion to insoluble derivatives or (ii) by encasing in rigid molecular environments using chelating agents. Alternatively, when very dilute, metal complexes are often innocuous. This method uses plants to extract and lower the concentration of toxic heavy metals in the soil. An aspirational method of decontamination of heavy metals is phytoremediation or bioremediation, but these approaches have solved few real world problems.

Toxic metals can bioaccumulate in the body and in the food chain. Therefore, a common characteristic of toxic metals is the chronic nature of their toxicity. This is particularly notable with radioactive heavy metals such as radium, which imitates calcium to the point of being incorporated into human bone, although similar health implications are found in lead or mercury poisoning.