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^[1]. Often heavy metals are thought as synonymous, but lighter metals also have toxicity, as exemplified by beryllium, and not all heavy metals are particularly toxic and some are even 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 imitate the action of an essential element in the body, distorting the metabolic process to cause illness. Many metals, particularly heavy metals are toxic, but some heavy metals are essential, have a low toxicity, and bismuth is even non-toxic. Most often the definition includes at least cadmium, lead, mercury and the radioactive metals. Metalloids (arsenic, polonium) may be included in the definition. Radioactive metals have both radiation 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.

The toxicity is a function of solubility, so that as insoluble salts or even in the metallic form, toxic metals may have negligible toxicity. On the other hand, organometallic forms, such as dimethyl mercury and tetraethyl lead, are extremely toxic.

Toxic metals bioaccumulate in the body and in the food chain. The exceptions are barium and aluminum. Therefore, a common characteristic of toxic metals is the chronic nature of their toxicity.

Toxic metals:

• Barium
• Beryllium
• Aluminum
• Cadmium
• Lead – lead poisoning
• Mercury – mercury poisoning
• Thallium
• Antimony
• Radioactive metals:
  • Thorium
  • Uranium
  • The transuraniums, such as plutonium, americium, etc.
  • Polonium (a metalloid)
  • Radioactive isotopes of lighter elements, e.g. cobalt-60.
• Arsenic (see arsenic poisoning) is a metalloid.

Trace elements with toxicity:

• Chromium as hexavalent Cr(VI)
• Nickel
• Copper
• Iron

• Dartmouth Toxic Metal Research Facility [1]

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