Mercury is a naturally occurring element that is toxic under certain conditions. Most of the mercury we worry about today comes from industrial pollution, especially from coal-fired power plants, but also from smelters, trash incinerators, and improper waste disposal. Factory smoke containing mercury can travel long distances before it falls from the air into streams, lakes, and oceans. Once in the water, certain bacteria convert the mercury into methylmercury, a dangerous neurotoxin that can harm a person’s brain, heart, kidneys, lungs, and immune system.

U.S. power plants account for about one percent of total global mercury emissions. There are several ways that coal-fired power plants can reduce their emissions of mercury. For example, scrubbers, filters, and other controls that limit sulfur dioxide, nitrogen oxides, and small particles can also remove some of the mercury before it is released from the smokestack. Some of these controls are more effective than others, depending on the type of coal that is burned and the design of the power plant.

The most advanced technology for removing mercury, called activated carbon injection, has been used in trash incinerators for years. Particles of activated carbon, which are injected into the waste gas, attach to the mercury and are removed. New technologies to reduce mercury emissions continue to be developed. Under the Clean Air Act, the Environmental Protection Agency (EPA) has the authority to regulate mercury emissions from power plants. The EPA is currently reviewing air toxics standards for coal- and oil-fired power plants and plans to create new guidelines.

As long as mercury is in the air, however, it is still a problem for people. How can you protect yourself? One of the most common ways people are exposed to mercury is by eating fish that contain high levels of mercury (in the form of methylmercury). The risks depend on the amount of fish eaten and the amount of mercury in the fish. You should not eat large predator fish, such as shark, swordfish, king mackerel, or tilefish, because they contain high levels of mercury that have accumulated in their tissues from eating prey fish contaminated with lower levels of mercury. However, it’s fine to eat two average meals a week of fish and shellfish that are lower in mercury, such as shrimp, salmon, pollock, and catfish. If your friends or family caught the fish, make sure to check local advisories about its safety.

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