Toxic metal

Toxic metals are metals that form poisonous soluble compounds and have no biological role, i.e. are not essential minerals, or are in the wrong form. Often heavy metals are thought as synonymous, but lighter metals also have toxicity, such as beryllium, and not all heavy metals are particularly toxic, and some are essential, such as iron. The definition may also include trace elements when considered in abnormally high, toxic doses. A difference is that there is no beneficial dose for a toxic metal with no biological role.

Toxic metals sometimes imitate the action of an essential element in the body, interfering with the metabolic process to cause illness. Many metals, particularly heavy metals are toxic, but some heavy metals are essential, and some, such as bismuth, have a low toxicity. Most often the definition includes at least cadmium, lead, mercury and the radioactive metals.^{[citation needed]} Metalloids (arsenic, polonium) may be included in the definition. Radioactive metals have both radiological toxicity and chemical 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.

Toxicity is a function of solubility. Insoluble compounds as well as the metallic forms often exhibit negligible toxicity. The toxicity of any metal depends on its ligands. In some cases, organometallic forms, such as methylmercury and tetraethyl lead, can be extremely toxic. In other cases, organometallic derivatives are less toxic such as the cobaltocenium cation.

Decontamination for toxic metals is different from organic toxins: because toxic metals are elements, they cannot be destroyed. Toxic metals may be made insoluble or collected, possibly by the aid of chelating agents. Alternatively, they can be diluted into a sufficiently large reservoir, such as the sea, because immediate toxicity is function of concentration rather than amount. However, bioaccumulation has the potential to reverse this.

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. The exceptions to this are barium and aluminium, which can be removed efficiently by the kidneys.

Toxic heavy metals

• Antimony (a metalloid)
• Arsenic (see arsenic poisoning) is a metalloid
• Barium
• Beryllium
• Cadmium - cadmium poisoning
• Lead - lead poisoning
• Mercury - mercury poisoning
• Osmium
• Thallium
• Vanadium
• Radioactive metals:
  • Actinium
  • Thorium
  • Uranium
  • Radium
  • The transuraniums, such as plutonium, americium, etc.
  • Polonium
  • Radioactive isotopes of metallic elements not otherwise strongly toxic, e.g. cobalt-60 and strontium-90.

Aluminium has no known biological role and its classification into toxic metals is controversial. Significant toxic effects and accumulation to tissues have been observed in renally impaired patients. However, individuals with healthy kidneys can be exposed to large amounts of aluminium with no ill effects. Thus, aluminium is not considered dangerous to persons with normal elimination capacity.

Vanadium poisoning is notable as it is an anti-corrosive component of automotive steel, fragments of which can be left in passengers during an automobile accident.

In cases of metal toxicity - especially from mercury via amalgam fillings and vaccines - chelation is seeing increasing therapeutic use. Perhaps the most-used method is the "Cutler Protocol", which uses constant doses of oral chelator only, and emphasises its conservatism and safety.

Trace elements with toxicity

• Chromium as hexavalent Cr(VI)
• Nickel – nickel salts are carcinogenic
• Copper – copper toxicity
• Zinc - zinc toxicity
• Iron – iron poisoning

Nonmetals

Some heavy nonmetals may be erroneously called "metals", because they have some metallic properties.

• Selenium – a nonmetal; essential element
• Tellurium

See also

• My Hang V. Huynh (chemist)

External links

• Dartmouth Toxic Metal Research Facility. http://www.dartmouth.edu/~toxmetal/
• OSHA. Safety and Health Topics: Toxic Metals. http://www.osha.gov/SLTC/metalsheavy/index.html