Mercury, a liquid metal – once widely referred to as quick silver – is a naturally occurring element released by volcanoes and the weathering of rocks. But most of the mercury that is responsible for polluting Minnesota lakes and the fish that live in them originates as air pollution from coal-burning power plants.
After mercury falls to Earth with rain, snow, or dust particles, bacteria convert it into a form called methylmercury. Without this conversion, the low concentrations of mercury in the environment would not be a problem. But methylmercury masquerades as an amino acid, so that animals retain it in their protein, and concentrations get higher and higher up the food chain. Plankton and small fish consume the methylmercury, and larger fish eat them. Fish highest on the food chain, such as bass, walleye and northern pike, end up with mercury concentrations about a million times higher than the water in which they live. Humans and fish-eating wildlife, such as loons and otters, are then exposed to elevated concentrations of mercury from consuming the fish.
From the early 1980s until the mid-1990s, mercury concentrations in fish were declining. But in February, 2009, the Minnesota Pollution Control Agency reported on a new study that showed mercury levels in large fish started to increase, on average, in the mid-1990s. For reasons scientists do not fully understand, mercury concentrations in fish are significantly higher in Northeastern Minnesota than in other parts of the state, even though the atmospheric mercury being deposited on lakes is relatively uniform across the state.
What problems does mercury cause?
Elevated exposure to mercury can harm the nervous system (brain, spinal cord and nerves) and the kidneys. It can cause illness or, in extreme cases, death, and it is a special concern for fetuses, infants and children, according to the Minnesota Health Department. Exposure to too much mercury during the time the nervous system is developing can affect a child’s ability to learn and process information.
In a famous environmental disaster, thousands of people in the Japanese town of Minamata have suffered from birth defects and other health problems as a consequence of eating fish from a bay where tons of mercury had been discharged in the 1950s and ‘60s.
The Minnesota Health Department encourages people to include fish as a regular part of their diet, but to consult consumption advice that is available and to choose fish that are low in contaminants. The agency offers general statewide fish-consumption advisories, as well as specific lake-by-lake advisories for lakes where fish have been tested for mercury. The advisories, available here , are divided into two categories:
* Women who are pregnant or may become pregnant, and children.
* Adult men and women who are not planning to become pregnant.
The advisories cover not only freshwater fish you might catch, but also saltwater fish you buy at the supermarket or order in a restaurant.
How much mercury pollution do we have?
The best data on how much mercury pollution occurs in Minnesota each year come from core samples that were taken from lakes in 1990. From those sediment cores, the Minnesota Pollution Control Agency estimates that about 6,000 pounds of mercury – about the weight of a full-size automobile — falls from the sky onto Minnesota each year. A much smaller amount–about 70 pounds in 1990, and much less now–is released directly into Minnesota waters from sewage treatment facilities and industrial plants each year.
The Minnesota Pollution Control Agency estimates:
* Forty percent of mercury in Minnesota lakes originates in North America from human activities, such as burning coal.
* Thirty percent comes from human-caused pollution in the rest of the world.
* Thirty percent comes from natural sources around the world.
Of all the atmospheric mercury that contaminates Minnesota surface waters, only about 10 percent originates in Minnesota. More than half of that comes from burning coal. While we receive mercury pollution from elsewhere, we also export mercury pollution from our smokestacks to other parts of the country and the world.
The good news is that Minnesota is taking big steps to reduce mercury emissions. A state plan adopted in 2007 calls for annual mercury emissions to be cut from an estimated 3,314 pounds in 2005 to 734 pounds in 2025. Many industries, but especially power plants and taconite mining, will have to make significant changes. Consumers will pay part of the cost of the reduction through higher electric bills – an estimated 55 cents to $1.55 a month for residential customers.
What can I personally do to help?
Conserve electricity. It will help reduce the need for burning coal.
We all know many older thermometers contain mercury. But so do many other products, including thermostats, fluorescent lights — both tubes and bulbs– high-intensity mercury vapor and sodium light bulbs, and some liquid crystal displays used in computer monitors and televisions.
If you break a mercury thermometer, thermostat or fluorescent bulb, take precautions and clean-up properly. The Minnesota Pollution Control Agency has a fact sheet that offers advice on preventing mercury contamination in the home.
Where can I get more information?
The web site for the Minnesota Pollution Control Agency has a very good Frequently Asked Questions page on mercury. The Health Department also offers information on mercury.