Mercury is a natural substance and is emitted into the atmosphere when many things are burned, especially coal at electric power plants. It also can come from burning products and garbage that contain mercury and naturally from volcanoes and evaporation from oceans.
Minnesota taconite plants also are a major source of mercury when ore pellets are hardened in giant furnaces.
Mercury falls back to the ground and in some cases becomes toxic, called methyl mercury, when it falls into waterways. That mercury then moves up the food chain from small organisms to fish and then animals that eat fish, including loons, otters and humans.
Exposure to high levels of mercury over a long period can cause severe neurological disorders, even death. Mercury also can cause major developmental problems in fetuses and small children.
The PCA and federal authorities have issued advisories for people to limit the number and size of fish meals they eat, especially women and children. Smaller fish usually have less mercury.
