Mercury (atomic weight 200.59) is a heavy, liquid at room temperature, silvery colored metal (density 13.53 g/mL). It presents the three oxidation states 0, +1, +2. The most modern uses are in batteries and cells. The Castner-Kellner process, that produces chlorine and sodium hydroxide, requires mercury in the entire process. It is furthermore used in thermometers, thermostats, switches, vacuum pumps, fluorescent and energy-saving lights, tooth fillings and electrical components. Many compounds of mercury have been used as medicines since many ages. However, in recent years, as awareness about the toxicity of mercury has increased amongst people, most of the medicines have become obsolete. Mercurochrome (used in cuts and wounds) and Thimerosal (as an dental amalgamation) are the compounds that are no more used in many countries. Mascara, an ingredient of cosmetics, contains some amounts of Thimerosal. During the past ten years mercury consumption has shown a strong upward trend. The major proportion can be accounted for by the chloro-alkali industry, from which mercury is released into the environment. Most of it finds its way to watercourses exposing aquatic ecosystems where mercury accumulates. The use of seed-dressings containing mercury is decreasing, although this use of mercurial’s is still considerable, and in view of findings in other countries elevated mercury levels in seed-eating birds and their predators must be expected. Many states in the US are now very strict against the use of mercury in cosmetics and medicines. Mercury in the form of gaseous vapors is used in mercury vapor lamps, neon signs and fluorescent lamps.

Biological properties of mercury are very important and include these characteristics: inhaled mercury is more dangerous than ingested mercury; human workers and handlers of mercury may become contaminated and mercury-diseased; elemental and inorganic

mercury can be transformed to the extremely toxic methyl-mercury (CH3Hg+) by some microbes; mercury accumulates in living organisms, cells, tissues, organs and organisms; mercury can damage immune cells and tissues, and organs such as brain, heart, kidneys, lungs; mercury can be concentrated in the environment and then magnified upwards along the food chain (bioaccumulation and bio-magnification); all compounds of mercury, except those not soluble in water, are to be considered poisonous regardless of the manner of inhalation or ingestion. Mercury limit in drinking water is 0.006 mg/L (WHO, 2008).