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Mercury in the Food we Eat
National Resources Defense Council

The most common source of mercury exposure for Americans is tuna fish. Tuna does not contain the highest concentration of mercury of any fish, but since Americans eat much more tuna than they do other mercury-laden fish, such as swordfish or shark, it poses a greater health threat.

Subsistence and sports fishermen who eat their catch can be at a particularly high risk of mercury poisoning if they fish regularly in contaminated waters. Across the United States, mercury pollution is known to have contaminated 12 million acres of lakes, estuaries, and wetlands (30 percent of the total), and 473,000 miles of streams, rivers, and coasts. And many waterways have not even been tested. In 2003, 44 states issued fish consumption advisories warning citizens to limit how often they eat certain types of fish caught in the state's waters because they are contaminated with mercury.

Know Where It's Coming From

The two biggest sources of mercury pollution are chlorine chemical plants and coal-fired power plants. Chlorine plants, which use massive quantities of mercury to extract chlorine from salt, "lose" as much as 100 tons of mercury each year; power plants emit around 50 tons of mercury pollution annually. Facilities that recycle auto scrap are another big source of mercury pollution, pouring 10 to 12 tons of mercury into the air every year. The most common way Americans are exposed to mercury is through tuna fish.

Power Plants

Coal is naturally contaminated with mercury, and when it is burned to generate electricity, mercury is released into the air through the smokestacks. The bulk of this mercury pollution could be eliminated with the installation of pollution-control devices. Similar devices have proved very successful on municipal incinerators, which were once a significant source of mercury pollution.

But in January 2004 the Bush administration proposed to weaken and delay efforts to clean up mercury emissions from the nation's 1,100 coal-fired power plants. Essentially, the administration's plan treats mercury as if it were a run-of-the-mill air pollutant instead of a hazardous air pollutant, allowing the Environmental Protection Agency to avoid requiring power plants to reduce emissions by the maximum amount technologically achievable.

Chemical Manufacturing

Big mercury polluters also include older mercury chlorine plants, also called chlor-alkali plants, which use mercury to convert salt to chlorine gas and caustic soda (better known as lye), which is used in soaps and detergents. More modern chlor-alkali plants use a cleaner, mercury-free technology. Only nine U.S. chlor-alkali plants continue to use mercury, but just these few contribute as much as 100 tons of mercury pollution per year. At any given time each plant has an average of 300 tons of mercury on site, and collectively the plants use as much as 100 tons of mercury annually to replenish the amount lost in the manufacturing process. They cannot account for where the "lost" mercury goes. Nor can the Environmental Protection Agency, but the agency has failed to set restrictions on these emissions.

Automobile Scrap

Mercury pollution also occurs when mercury-based light switches from automobiles are scrapped and melted down for recycling. As the switches melt, the mercury they contain vaporizes into the air.

Following considerable public pressure, auto manufacturers stopped using mercury in January 2003. But as long as older cars are incinerated, mercury pollution will continue to escape into the air. To prevent this, mercury-based car switches should be removed at the scrap yard, before cars are shredded and sent to steel mills for recycling. Removing the switches would take less than a minute per car, on average -- a cost that should be borne by the companies that installed them in the first place, not by the scrap industry.

Time On Our Side
While mercury is a so-called persistent pollutant, meaning that it doesn't break down as some other pollutants do, its dangers lessen considerably over time, because it eventually settles into the beds of rivers, lakes and oceans and is covered over by successive layers of sediment. At some point, fish stop consuming the mercury so eventually it ceases to be a hazard to humans.

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