What is Mercury?
Mercury is a naturally-occurring chemical element found in rock in the earth’s crust, including in deposits of coal. On the periodic table, it has the symbol “Hg” and its atomic number is 80. It exists in several forms:
- Elemental (metallic) mercury
- Inorganic mercury compounds
- Methylmercury and other organic compounds
Inorganic Mercury
In its inorganic form, mercury occurs abundantly in the environment, primarily as the minerals cinnabar and metacinnabar, and as impurities in other minerals. Mercury can readily combine with chlorine, sulfur, and other elements, and subsequently weather to form inorganic salts. Inorganic mercury salts can be transported in water and occur in soil. Dust containing these salts can enter the air from mining deposits of ores that contain mercury. Emissions of both elemental or inorganic mercury can occur from coal-fired power plants, burning of municipal and medical waste, and from factories that use mercury. Inorganic mercury can also enter water or soil from the weathering of rocks that contain inorganic mercury salts, and from factories or water treatment facilities that release water contaminated with mercury.
Methylmercury
When inorganic mercury salts can become attached to airborne particles. Rain and snow deposit these particles on land. Even after mercury gets deposited on land, it often returns to the atmosphere, as a gas or associated with particles, and then redeposits elsewhere.
As it cycles between the atmosphere, land, and water, mercury undergoes a series of complex chemical and physical transformations, many of which are not completely understood. Microscopic organisms can combine mercury with carbon, thus converting it from an inorganic to organic form. Methylmercury is the most common organic mercury compound found in the environment, and is highly toxic.