<unk>  or<unk>  poisoning is the toxic effect of certain<unk> s in certain forms and doses on life. Some<unk> s are toxic when they form poisonous soluble compounds. Certain<unk> s 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. It is often thought that only heavy<unk> s can be toxic, but lighter<unk> s such as beryllium and lithium may also be in certain circumstances. Not all heavy<unk> s 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<unk>  poisoning may be chelation therapy, a technique involving the administration of chelation agents to remove<unk> s from the body. Toxic<unk> s sometimes imitate the action of an essential element in the body, interfering with the<unk> olic process resulting in illness. Many<unk> s, particularly heavy<unk> s are toxic, but some heavy<unk> s are essential, and some, such as bismuth, have a low toxicity. Most often the definition of toxic<unk> s includes at least thallium, cadmium, manganese, lead, mercury and the radioactive<unk> s.<unk> loids (arsenic, polonium) may be included in the definition. Radioactive<unk> s have both radiological toxicity and chemical toxicity.<unk> s 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<unk> lic forms often exhibit negligible toxicity. The toxicity of any<unk>  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<unk> s is different from organic toxins: because toxic<unk> s are elements, they cannot be destroyed. Toxic<unk> s may be made insoluble or collected, possibly by the aid of chelating agents, or through bioremediation. Alternatively, they can be diluted into a sufficiently large reservoir, such as the sea, because immediate toxicity is a function of concentration rather than amount. Another method of decontamination of heavy<unk> s in the soil is using a method called phytoremediation. This method uses plants to extract and lower the concentration of toxic heavy<unk> s in the soil. Toxic<unk> s can bioaccumulate in the body and in the food chain. Therefore, a common characteristic of toxic<unk> s is the chronic nature of their toxicity. This is particularly notable with radioactive heavy<unk> s 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.
Metal toxicity
Copper toxicity
Zinc toxicity
Chromium toxicity
Fluoride toxicity
Chromium deficiency
Boron deficiency 
Lead poisoning