Mercury and its compounds
Mercury is a silvery-white metal that is liquid at room temperature. It freezes at -39 0C and it boils at 357 0C at atmospheric pressure. Mercury is appreciably volatile. It is odourless and not flammable. Mercury forms a number of inorganic and organic compounds notably mercuric and mercurous chlorides and methyl mercury.
Mercury has been known since antiquity. It rarely occurs as the free metal in nature. The main ore from which mercury is extracted is cinnabar (mercuric sulphide), found predominantly in Italy and Spain. The organic and inorganic forms of mercury may inter-convert over time: organic mercury compounds may slowly be oxidised to form inorganic mercury while inorganic mercury compounds may be transformed into organic mercury forms by bacteria in soil and water.
Mercury is used in the manufacture of thermometers, barometers, diffusion pumps and other instruments. It is also used in making mercury-vapour lamps and advertising signs, and in mercury switches, batteries and other electrical apparatus. Other uses are in the chlor-alkali industry and in dental fillings.
Former uses in many industry sectors have now been phased out.
Main sources of releases of mercury to the atmosphere are waste incineration, non-ferrous metal production, coal combustion, crematoria (due to the use of the metal in dental fillings) and chlorine manufacturing plants using mercury cells. Mercury is also released to waste water by industrial processes using the metal and its compounds and from dental surgeries, hospitals and clinics. Since mercury occurs as an element in the earth's crust, releases to the environment also result from natural sources.
Impacts on human health and environment
Excessive exposure to mercury and its compounds may cause effects on the brain, digestive system, eye, heart, kidney, lung, reproductive system, skin, and the unborn child.
Organic compounds of mercury are very toxic to wildlife, while the metallic form and the inorganic compounds are less toxic. Organic mercury compounds tend to bioaccumulate and can have adverse effects on aquatic species. Low levels of mercury contamination in lakes can lead to high concentrations in insects, fish and birds. Mercury is also toxic to plants and micro-organisms, hence its former use as a fungicide and bactericide. However, hazards depend upon the form and bioavailability of mercury.
Because of the persistence and bioaccumulation potential of mercury and its compounds in the environment, mercury is regarded as a global pollutant. Mercury and its compounds are listed as priority hazardous substance in of the Water Framework Directive.
Emission to air reporting threshold: 10 kg/year
Emission to water reporting threshold: 1 kg/year
Data source: European Pollutant Emission Register