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I remember as a kid playing with mercury from a thermometer after it broke. My brothers and I liked to watch it roll around and split into pieces. Not a good idea!

Last year, when a thermometer broke in my home, I kept my kids away from it, and called the health department to find out how to carefully clean it up and where to take it for disposal. I now know much more about the dangers of mercury and that mercury can pose a health risk to people and wildlife. Let me tell you what I've learned.

Mercury poisoning affects the human brain, spinal cord, kidneys, and liver. Long-term exposure to mercury can result in symptoms that get progressively worse and can lead to personality changes, stupor, and coma. Children are more sensitive to mercury poisoning than adults and are more likely to have serious effects from exposure to mercury vapor.

You might be surprised to learn where mercury is found in your home and school. Thermometers (fever, cooking, outdoor), thermostats, fluorescent lamps, button batteries, and some switches or relays can all be a source of mercury.

You can help stop mercury pollution. Here are a few tips.

  • Don't put mercury or mercury-containing products in the trash or down the drain.
  • Conserve energy in order to reduce the mercury released from coal-fired electricity plants.
  • Identify items in your home that contain mercury. Label the items with a small sticker that says "Contains Mercury-Dispose of Properly." When your parent or guardian is ready to replace the mercury-containing devices have them use mercury-free alternatives like the following.
    • Thermometers. Buy non-mercury thermometers.
    • Thermostats. Replace mercury thermostats (the round style and others) with a digital thermostat.
    • Fluorescent and mercury vapor lamps. These lamps save a lot of energy, but the mercury in them must be properly recycled. Store and mark the lamps in a way to prevent breakage and take the lamps to a lamp recycler.
    • Mercury switches. Buy the kind of light switches that click, rather than the "smooth" switches.
    • Lighted tip-ups for ice fishing. Avoid creating more fish advisories by using a regular tip-up.

Mercury in the Environment

Mercury occurs naturally and is found in very small amounts in oceans, rocks, and soils. It becomes airborne when rocks erode, volcanoes erupt and soil decomposes. It then circulates in the atmosphere and is redistributed throughout the environment.

Large amounts of mercury also become airborne when coal, oil, or natural gas are burned as fuel or mercury-containing garbage is incinerated. Once in the air, mercury can fall to the ground with rain and snow, landing on soils or water bodies, causing contamination.

In the mid-1970s, biologists sampling fish in northern Minnesota and Wisconsin found mercury in high levels, but they didn't know where it was coming from. It took a decade of research to find out it was coming from the air, especially from coal-burning power plants and waste incinerators. Mercury attaches to tiny raindrops that settle after one or two years of floating in the atmosphere.

This was similar to our nation's struggle with acid rain, which affects some of our cleanest, most remote lakes. In fact, it was acid rain research that first showed scores of fish tainted by mercury.

Beginning around 1990, scientists realized lake acidity wasn't the only thing affecting mercury in lakes-it was also the bacteria that thrived in those waters. Lakes that are more acidic contain bacteria that convert mercury falling from the sky into methylmercury-an organic form that is easily absorbed by the tiniest plants and animals. And, the same bacteria can live in less acid environments if certain conditions are present. These include low oxygen levels from decomposing plants and higher sulfides. The best places to find such conditions are in wetlands. So, if a lake or river has a wetland feeding water into it, the water is more likely to be tainted with methylmercury.

On its spread through the food web, mercury levels rise in each predator. This process, called bioaccumulation, can result in a level of mercury in the topmost predator many times greater than the original amount in surrounding waters. Thirty-nine states, including Wisconsin, warn residents not to eat certain species of fish caught in some lakes, rivers, and streams because of high levels of mercury.

Mercury in Fish

Once in a lake or river, mercury is converted to methylmercury by bacteria and other processes. Fish absorb methylmercury from their food and from water as it passes over their gills. Mercury is tightly bound to proteins in all fish tissue, including muscle. There is no method of cooking or cleaning fish that will reduce the amount of mercury in a meal.

Methylmercury accumulates as you move up the food chain.

  1. Tiny animals and plants known as plankton take up methylmercury in the water and sediment.
  2. Minnows and juvenile fish eat large quantities of plankton over time.
  3. Large predatory fish consume many smaller fish, accumulating methylmercury in their tissues. The older and larger the fish, the greater the potential for high mercury levels in their bodies.
  4. Fish are caught and eaten by humans and animals, causing methylmercury to accumulate in their tissues.

In Wisconsin and Michigan lakes, the highest methylmercury levels are found in large walleyes. High mercury levels may also be found in largemouth bass and northern pike. Panfish, such as perch and bluegill, contain the lowest levels.

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