What is Mercury? Environment & Health Mercury Sources Mercury Emissions Allowable Emissions Future Emission Levels Reduction Efforts Technology Advances

Mercury is a naturally occurring heavy metallic element. As an element, mercury cannot be broken down, diluted, or entirely eliminated from the environment. It is found in minute amounts in oceans, rocks, and soil as well as in fossil fuels. It becomes airborne when rocks erode, volcanoes erupt, soil decomposes, and when fossil fuels are burned. It then circulates in the atmosphere to be redistributed throughout the environment.

Mercury exists naturally in different physical and chemical forms. Elemental or metallic mercury, sometimes referred to as quicksilver, is the purest form of mercury and not normally found in nature. It is a volatile metal that can be in the form of gas, liquid, or solid, and is the only heavy metal that exists as a liquid at room temperature. At room temperature, this liquid form of mercury will evaporate into the atmosphere.

In nature, mercury exists most commonly as inorganic mercury compounds, or mercury salts. Mercury, in the inorganic form, is relatively biologically inactive.

Natural processes can also change one form of mercury into another. Normal chemical reactions can transform elemental mercury into inorganic mercury. Microscopic organisms change inorganic mercury into organic mercury, the most common of which is methylmercury. Mercury in the form of methylmercury accumulates in fish and from there into mammals that eat fish.

Mercury has high electrical conductivity and expands and contracts evenly with temperature. Due to these unique qualities, mercury is used in thousands of industrial, agricultural, medical, and household applications. We use mercury in many products and it is released to the environment from many sources: household and commercial products, industrial processes, coal-fired power plants, incinerators, some manufacturing plants, hospitals, dental offices, schools, and even homes have all been found to release mercury. In the home, mercury can be found in fluorescent lights, thermostats, thermometers, and even some children's toys. At school, mercury may be in science and chemistry classrooms, the nurse's office, and in electrical systems.

Large amounts of mercury also become airborne when we burn coal or oil as fuel or burn mercury-containing garbage. Airborne mercury can fall to the earth with rain and snow, eventually reaching lakes and rivers, causing contamination. Once present in rivers and lakes, mercury accumulates in fish and increases up the food chain in a process of bioaccumulation or biomagnification. Mercury-contaminated fish can ultimately reach the dinner table, which is a major health concern.

Although coal is not the only anthropogenic, or man made, producer of mercury emissions, it is the largest source. We have significantly reduced the amount of overall emissions in this country and we will reduce mercury emissions from coal-fired power plants through new technology and awareness. Continued research is making significant advances in developing technologies to remove mercury from utility emissions.