What is Mercury and Where Does it Come From?

Mercury (Hg) is an element that occurs in the environment naturally as a result of human activity. It is a silvery color and the only metal that is liquid and room temperature. It is considered one of the "heavy metal" because of its atomic weight and can be found as number eighty on the periodic table of elements. Mercury can also evaporate to form an odorless, colorless, vapor. Mercury has proved useful for measuring devices such as thermometers, but is toxic to humans and animals.

The erosion of rocks, eruption of volcanoes and decomposition of soil lead to the to the admission of mercury into the air. While natural levels of mercury have never been a threat to humans or animals, man-made levels are. The main and most problematic source of mercury admission comes from power plants that burn fossil fuels; primarily coal.


In Wisconsin, the Department of Natural Resources estimates that over 60% of the mercury in the state's natural water systems is a direct result of coal-fired power plants. Sediment studies of the bottom of northern Wisconsin lakes showed a four-fold increase in mercury levels since the late 19th century, when industry first came to our state. Because mercury is a basic element, it cannot be treated, reduced or destroyed. Mercury that falls on Wisconsin in the form of precipitation could be from anywhere in the world. Some airborne mercury floats across the planet until it is absorbed by the atmosphere and precipitates. Studies by the EPA have shown significantly more levels of mercury in the northern hemisphere as opposed to the southern due to the increased industrialization of countries that lie in the north.

Research on a northern Wisconsin lake found that as little of one gram of mercury per year was enough to contaminate the lake's entire fish population. When mercury enters the water, it can combine with organic materials to form organic compounds such as methylmercury (MeHg), which is produced mainly by bacteria and is the form that poses the greatest risk to environmental exposure. The process by which mercury contaminates fish is very complex. Simply put, tiny organisms absorb mercury. Small fish eat the tiny organisms; big fish eat the small fish and so goes the food chain heirarchy. By a process called biomagnification, mercury levels increase as they move up the food chain. Ultimately, mercury levels in humans are the greatest, as we are at the top of the food chain.