Some of the sources of mercury pollution include metal smelting, chlorine chemical plants, cement plants, and coal-fired power plants. Power plants are the largest source, emitting around 50 tons of mercury pollution annually. Cement plants are the fourth largest emitter of airborne mercury in the United States, and facilities that recycle auto scrap are another big source of mercury pollution, historically pouring 10 to 12 tons of mercury into the air every year. Chlorine plants, which use massive quantities of mercury to extract chlorine from salt, "lose" mercury when mercury volatilizes during maintenance and other operational activities. 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.

In 2009, NRDC and several environmental allies achieved an enormous victory when the EPA settled a lawsuit to finalize a Maximum Achievable Control Technology (MACT) standard by November 2011, reducing all hazardous air pollutants, including mercury, from the nation's coal- and oil-fired power plants. The revised standards will facilitate long-delayed efforts to clean up mercury emissions from roughly 1,100 coal-fired boilers at more than 460 electric power plants.

Chemical Manufacturing

Older mercury chlorine plants, also called chlor-alkali plants, use mercury to convert salt to chlorine gas and caustic soda (better known as lye), which is used in soaps and detergents, in plastics, and in the paper-making process. At any given time, each of these plants may average about 200 tons of mercury on site. Historically, chlor-alkali plants have "lost" dozens of tons of mercury in the manufacturing process. These plants cannot account for where the lost mercury goes, nor can the Environmental Protection Agency.

More modern chlor-alkali plants use a cleaner, mercury-free technology, but four U.S. chlor-alkali plants continue to use mercury. Two of these plants have announced plans to shift to cleaner technologies, and the remaining two may be closed under a strengthened air toxics standard recently proposed by the EPA.

Cement Plants

Cement plants are the fourth largest emitter of airborne mercury in the United States. In regions where there is little coal fired power generation, such as California, the contribution of cement plants to airborne mercury emissions from human activity is greater, 75 - 90 percent. In 2007, U.S. cement plants emitted 11,177 pounds of mercury. Mercury from cement plants is emitted primarily from coal burnt to fire the kilns and from the heating of limestone that contains mercury. Limestone is one of the raw materials used to produce cement.

On August 6, 2010, the EPA finalized standards for emissions of mercury and other air toxics that are expected to reduce mercury emissions by 16,600 pounds, a 92 percent reduction from projected 2013 emission levels. The standards are expected to reduce the amount of mercury deposited on land and water by up to 30 percent in some areas of the western United States, and 17 percent in some areas of the eastern United States.

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 is quickly and easily done. Incentives should be provided borne by the companies that installed them in the first place to encourage maximum removal rates. Fortunately, there is now a voluntary national program to collect vehicle mercury switches, but the program needs more funding and other improvements to improve switch capture rates. More information on the switch removal program can be found at the ELVS Mercury page and in the ECOS NVMSRP Status Report.

Global Sources of Mercury

Chlor-alkali plants are among biggest users of mercury worldwide. The good news is that the chlorine industries in both India and the European Union, where a large number of mercury-based chlor-alkali plants are located, have made voluntary commitments to phase-out the mercury process completely.

Unfortunately, other uses of mercury are on the rise. High demand for polyvinyl chloride (PVC) from China's booming construction industry has fueled growing demand for the mercury catalyst used in PVC production. Small scale (artisanal) gold miners around the world, especially in Asia, Africa and South America, use mercury to bind with gold contained inside ore, and then burn off the mercury, leaving just the gold behind. This low-tech practice releases a significant quantity of mercury to the air, causes severe damage to soils, water bodies and wildlife near the mining sites, and results in heavy mercury exposures to the miners and their families. Mercury is also still commonly used around the world in batteries, measuring devices, electrical switches, dental amalgam, and some traditional medicines and arts.

Coal-fired power plants are the largest source of mercury air emissions worldwide. As the price of oil rises, coal becomes a more economically attractive source of energy in countries where it is abundant and inexpensive. Currently, coal-fired power plants supply 75 percent of China's energy; in the next eight years, China is expected to add more coal plants to meet domestic energy demand. However, China recently proposed mercury emission limits on new coal-fired power plants.

Mercury in the Food We Eat

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. (For more, see our guides to mercury levels in fish and to eating tuna safely.)

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 has contaminated 18 million acres of lakes, estuaries, and wetlands (43 percent of the total), and 1.4 million river miles. From 2006 to 2008, the number of lake acres under advisory increased by 18 percent, and the number of river miles increased by 52 percent. And many waterways have not even been tested. In 2008, all 50 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.

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.

We can begin safeguarding our health now by stopping mercury pollution at its sources.

Intro | Effects | Sources | Protect Yourself | For Medical Professionals