Mercury in the environment

Sources

Mercury is a naturally occurring element found in oceans, mineral rocks, fossil fuels and soil. It can become airborne and redistributed throughout the environment when minerals are processed, fossil fuels are burned, rocks erode, volcanoes erupt and by sun and rain acting on soils. Mercury has been around for thousands of years and has been extracted from minerals and used by humans since Roman times.

Uses

Mercury is used in small amounts in household and commercial products, such as fluorescent lights, thermostats and thermometers, as well as in industrial processes. As a result, some manufacturing plants, hospitals, dental offices, schools and even homes inadvertently release mercury. In addition, when mercury-containing products are disposed, mercury can be released by incinerators that burn these discarded items.

Power production

Trace amounts of mercury are present in coal and oil. Consequently, when these fuels are used to generate electricity, some of this mercury is released into the air. Power plant emissions account for about one-third of the mercury emitted into the air by all sources in the U.S., but according to U.S. Environmental Protection Agency (EPA), accounts for only about 1 percent of the mercury emitted by global human activities. Researchers are trying to determine how much mercury from power plants actually enters aquatic environments, as well as how much of it actually enters the aquatic food chain. This is difficult because mercury has so many sources.

Mercury levels in ecosystems

Mercury levels in Midwest lakes, including Lake Michigan and Lake Superior, appear to be declining because mercury use is decreasing. For example, since 1980, We Energies has voluntarily reduced the use of mercury-containing equipment in power plants by about 10,000 pounds. This decline continues despite increasing coal use during the past several decades.

Health effects

• Mercury in the air and water
  Like many pollutants, mercury and certain of its many compounds can be toxic to humans at certain levels. Mercury is present in air and water but at concentrations not considered a health threat. When certain forms of airborne mercury settle in aquatic systems, mercury can be converted into a form (methyl-mercury) that accumulates in fish, which then can be absorbed by humans who eat these fish.
• Mercury in fish
  Health experts are trying to determine a safe level for mercury consumption given that mercury and its toxic forms are naturally occurring substances, and that mercury, in varying amounts is present in all fish. Further, even people who consume large amounts of certain marine fish or shellfish may not be at an increased risk of health effects according to studies recently completed by U.S. EPA. In addition, a study of more than 700 mother/child pairs conducted in the Seychelles Islands (a group of islands in the western Indian Ocean) showed no health effects even though this population eats ocean fish nearly every day.

Routine mercury exposure via fish consumption among the general population in North America is considered to be of little health concern by U.S. EPA. Humans, other mammals and birds have evolved defense mechanisms to rid the body of small amounts of mercury. However, too much mercury can lead to many health problems, including a form of palsy, which can develop in an infant fetus when the mother has been exposed to very high mercury levels. Mercury poisoning can be fatal in extreme cases of very high exposure. The severe instances of mercury poisoning that are frequently cited have occurred when individuals have been directly exposed to high levels of mercury as a result of consuming contaminated grains (mercury has been used as a fungicide) or fish from waters where large discharges (tons) of mercury compounds have occurred.

• Protection measures
  State and federal agencies' fish advisories provide guidance for fish and seafood consumption, particularly for pregnant women. The U.S. EPA and the U.S. Food and Drug Administration believe that eating one to four meals per week of most commercial fish is not likely to pose risks of adverse health effects for any individuals, including pregnant women and their young children.
• Useful resources concerning mercury health effects:
  Clean Air Mercury Rule (U.S. EPA)
  Annapolis Center for Science-based Public Policy

Mercury controls for power plants

• Power plant emissions
  Measurements at a number of U.S. power plants suggest existing emission control devices for particulates and sulfur dioxide capture on average 40 percent of mercury present in emissions. However, the amount captured at any one plant can vary between 0 and 98 percent. The variation is related to the type of coal burned and the emission control equipment. The amount of mercury present in the coal and the chemical form of the mercury produced when the coal is burned in the boiler largely dictate capture by existing emission control devices. For We Energies’ plants, the approximate amounts currently captured vary between 0 and 80 percent.
• Controlling emissions
  We are actively involved in efforts to advance mercury control technologies for power plants and to develop workable state and federal mercury control rules. We conducted several research projects at our Pleasant Prairie Power Plant near Kenosha, Wis., and completed a major mercury control technology demonstration project at our Presque Isle Power Plant in Marquette, Mich. The work at both project sites provides valuable information on mercury controls for the entire electric power industry.

As part of our integrated air quality strategy, we have adopted solutions that combine various control technologies to achieve reductions for multiple emissions, including sulfur dioxide, nitrogen oxides and mercury. In addition to projects at existing plants, mercury emissions from the new Elm Road Generating Station units in Oak Creek, Wis., will be controlled by more than 90 percent.

• Useful resources

Mercury Control Demonstration Project at Presque Isle Power Plant (PDF 269k) (We Energies)
Mercury Answers (Edison Electric Institute)
Controlling Power Plant Emissions (U.S. EPA)
Mercury Emission Control (National Energy Technology Laboratory)