Mercury (Hg) in blood.

Mercury is an element that exists in three forms. The metal mercury (in liquid or gaseous form) is often used for dental fillings and in thermometers and batteries.  Mercury can form inorganic compounds (mercury salts) with other elements such as oxygen or sulfur. In this form, it is found in crystalline form and is sometimes included in topical preparations such as skin lighteners or antiseptic creams. Mercury combines with carbon to form organic substances, the most common of which is methylmercury. These substances are produced by bacteria that live in soil and water. Elevated levels of this form of mercury are often found in large, predatory, non-juvenile fish such as sharks and king mackerel. The test determines mercury levels in the blood to diagnose acute poisoning or chronic exposure to mercury in the body.  Mercury is found in small quantities in the environment. It is released through the breakdown of rock and soil minerals and as a by-product of fuel fires and the burning of rubbish.  Mercury can enter the body from the air we breathe, through the skin, or through food. The minute concentrations of this metal that most people encounter in their daily lives do not pose a health risk. However, its high content, e.g. in toxic waste storage facilities, as well as regular prolonged contact with moderate amounts of it, as with heavy metals, can lead to poisoning.