Know Where It's Coming From
Each year power plants and other sources create tons of mercury pollution, which makes its way into our homes and bodies in fish.
Some of the major sources of mercury pollution in the US include coal-fired power plants, boilers, steel production, incinerators, and cement plants. Power plants are the largest source, emitting around 33 tons of mercury pollution in the US annually, and contributing to almost half of all mercury emissions. Large boilers and heaters, many of which are powered by coal, are the next largest source of mercury emissions, followed by steel production. Incinerators, once the largest source of mercury in the U.S. have drastically reduced emissions, though they remain the fourth largest source. Overall, mercury emissions have gone down by 65 percent in the US over the past two decades.
Power Plants and Coal Combustion
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 relatively simple and widely-available pollution-control devices. Similar devices have proved very successful on municipal incinerators, which were once a significant source of mercury pollution. In the United States, mercury pollution from power plants and industrial sources collectively contributes to half of all the mercury air emissions.
Regulation of mercury pollution has finally begun to phase in among the largest emitters despite long delays and repeated attempts to weaken mercury regulations under the Clean Air Act. The Environmental Protection Agency finalized clean air safeguards to reduce toxic pollution, including mercury, from:
- cement plants in 2010,
- power plants in 2011,
- gold mining in 2011, and
- industrial boilers in 2013, but these are now on hold due to litigation.
New standards were proposed for the chlorine chemicals industry in 2011. Mercury emissions are slated to go down 80 percent by 2016 compared to 1990 levels, due to these US EPA regulations.
Outside the U.S., coal-fired power plants are the largest source of mercury air emissions worldwide. Coal is an 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 issued mercury emission limits on new and existing coal-fired power plants which will be implemented over the next few years.
In the U.S. large scale mining and processing of gold ore is a now a relatively minor source of direct mercury emissions to air thanks to effective regulations. Globally, however, large scale gold mining still emits substantial quantities of mercury to the environment. In addition, the largest use of mercury in the world is artisanal and small scale gold mining. Approximately 10-20 million 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, and adds to the global pool of mercury in the environment.
Manufacturing of Metals and Cement
Mercury is an impurity in certain metal ores, and in limestone, which is used to make cement. As noted above, mercury can also be in the coal that is often burned to power cement kilns. Accordingly, metal smelting and refining, particularly lead and zinc smelting, and cement manufacturing, are significant contributors to global mercury pollution.
Other Industrial Mercury Emitters
Certain types of chemicals, such as chlorine, were originally produced using a mercury intensive process. This 19th century technology is still employed at up to 100 "chlor-alkali" plants around the world as of 2011, accounting for approximately 15% of mercury use worldwide. Because an alternative process is widely available, chlor-alkali plants represent a significant source of preventable mercury pollution. There is some good news: The chlorine industry has phased out mercury use in India, where a large number of mercury-based chlor-alkali plants were located. In the US, just two of these outdated mercury based chlor-alkali plants are left.
A large percentage of the polyvinyl chloride, or PVC, manufactured in China relies on a coal-based method that uses mercury as a catalyst. China's PVC industry is one of the largest users of mercury worldwide, consuming over 800 metric tons annually, and releasing substantial quantities of mercury throughout the catalyst life cycle. Pilot testing of a mercury free catalyst is now underway in China.
Consumer Products and Additives
Mercury is used as a component in many consumer products, like thermometers, batteries, electronic devices and many automotive parts, and can escape as a pollutant when these products are manufactured, broken during use, or most importantly, handled and disposed of at the end of the product's useful life. It can also be used as an additive to cosmetics and antiseptics, often exposing consumers unknowingly and unnecessarily. Incinerators burning mercury wastes, including discarded products, can release significant quantities of mercury unless they are equipped with appropriate mercury capture devices. Likewise, the recycling of scrap metal (secondary smelting) can release mercury from auto parts like light switches, if proper care is not taken to remove the mercury before smelting and/or mercury capture devices are not installed on the smelter.
Mercury in the Food We Eat
Release of mercury into the environment starts a dangerous sequence towards humans' primary exposure to mercury pollution: the consumption of fish. Mercury pollution can make its way to oceans and waterways, contaminating fish and seafood, and accumulating in higher concentrations as it makes its way up the food chain.
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.
We can begin safeguarding our health now by stopping mercury pollution at its sources and keeping a close watch on which fish and how much we eat.
Photo: top, Getty Images
Use the pull-down menu below to find state and local fish advisories.
Use NRDC's Mercury Calculator to find out if you're consuming too much mercury.
If you are pregnant or planning to become pregnant, use this guide to see what amounts of fish caught and sold commercially are safe to eat.
Mad as a Hatter about Mercury
The "Mad Hatter" of Alice in Wonderland didn't get his name by accident. Hat-makers used to use mercury to strengthen their hats, and in the process breathed in mercury vapors.
Mercury is the only metal that is liquid at room temperature. Exposed to air, it will evaporate, creating very dangerous mercury vapors.
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