The five lakes - Huron, Michigan, Erie, Ontario and Superior - cover 94,000 square miles and make up 20 percent of the world's freshwater. Lake Michigan is the only lake located entirely in the United States, the other four lakes share the international border between the U.S. and Canada. The Great Lakes basin is the most ecologically diverse freshwater system of its kind and it's wellbeing is necessary to both wildlife and humans who live in and around its shoreline.
Mercury is a naturally occurring element that is found in cinnebar, volcanic eruptions, forest fires and many rocks including coal. Human activities, such as coal-fired power plants and manufacturing, have drastically increased the amount of mercury in the environment.
Mercury in the air, from various sources, can settle in the water or on the land where it's washed into the Great Lakes or tributaries. Once its in the water, microorganisms take it into their system and convert it into methylmercury, a toxic form of mercury. As methylmercury moves up the food chain, from shellfish to frog to fish to human, it accumulates in the tissues and becomes more toxic. Fortunately, the levels of methylmercury in fish and shellfish depend on how long they live, where they are in the food chain and what they eat.
Humans become exposed to methylmercury when they eat shellfish and fish from the Great Lakes. If they eat large amounts of fish from the Great Lakes, like some Native American tribes, there is an increased level of mercury in their blood and/or body tissues. The effects of mercury poisioning have resulted in development defects and neurological problems in fetuses and infants including cerebral palsy, and nervous system problems in adults. Exposure to mercury can also lead to nausea, loss of color vision, kidney damage, tremors, paralysis and even death.
Since 1972 the U.S. and Canada have entered into joint agreements designed to reduce or rid the Great Lakes of persistant toxic substances including mercury. Though progress has been made since then, much more research needs to be done. One of the most noteable achievements is the Clean Water Act which is regulated by the Environmental Protection Agency (EPA) and has developred water quality citeria for human health and aquatic life in the Great Lakes states. the EPA has also issued water quality criteria for methyl mercury that is used by states to determine acceptable levels of methyl mercury in fish and fish tissues.
Like the U.S., Canada EPA has also taken steps to reduce the release of chlor-alkali mercury and paper-pulp factories. Mercury based paint has also been prohibited for children's toys. The Hazardous Products Act prohibits the use of mercury or its compounds as paint on children’s toys. One of the largest sources of mercury is still mercury thermometers; and while some companies have stopped selling them Canada hasn't officially banned them yet.
The U.S. has also developed two pretreatment standards for toxic substance release from industries, categorical - which are industry specific and applied on a national level, and local limits - which apply to all industries in the general area . The sale of mercury therometers has been banned in many states and batteries have also been added to the list to reduce the release of mercury. The most recent and perhaps most important mercury ruling in 2004 seeks to permanently cap and reduce mercury emissions from coal-fired power plants.