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About Environmental Mercury

About Environmental Mercury

Bacteria and chemical reactions in lakes and wetlands change the mercury into a much more toxic form known as methylmercury. Fish become contaminated with methylmercury by eating food (plankton and smaller fish), which has absorbed methylmercury.

As long as the fish continue to be exposed to mercury, mercury continually builds up in their flesh. Fish that eat other fish become even more highly contaminated. Thus, the fish most desirable for many anglers -- bass, walleye and northern pike -- become the most affected, and larger fish tend to be the most contaminated.

When people eat the contaminated fish, the methylmercury remains in their bodies for a long time. If they eat fish containing methylmercury faster than their bodies can get rid of it, the methylmercury accumulates in their bodies and can be toxic. Many states, including Minnesota, have fish consumption advisories to inform people about how many meals of fish they can safely eat over a period of time.

• Eat Fish Often? A Minnesota Guide to Eating Fish
• Minnesota's Fish Contaminant Monitoring Program
• Sources of Mercury Pollution and the Methylmercury Contamination of Fish in Minnesota

Where Mercury Comes From

Mercury is a naturally occurring element. Mercury ore - cinnabar - is mined in Spain, Algeria, Kyrgyzstan and China. Mercury is also a by-product of gold and zinc mining. Mercury enters the environment from:

• Natural sources such as volcanoes and the weathering of rocks;
• Our intentional uses of mercury;
• Our unintentional releases of mercury from burning fossil fuels and smelting metals.

Mercury's Uses

• To produce chlorine and caustic soda;
• In wiring devices and switches
• For electric lights;
• For measuring and control instruments (such as blood pressure gauges and thermometers);
• Others

Mercury can also escape to the environment when items containing mercury are broken or thrown away. Whether the items are dumped in sewers, garbage cans or burned, some of the mercury will eventually enter the atmosphere and later end up in lakes or oceans, where it can accumulate in fish.

Mercury is also a pollutant in the air emissions from activities such as burning coal and producing taconite. A number of other possible sources of mercury exist, including cement plants and gasoline combustion.