Where are the Great Lakes?

The five lakes – Huron, Michigan, Erie, Ontario and Superior – cover 94,000 square miles and make up 20% of the world’s freshwater. Lake Michigan is the only lake located entirely in the United States; the other lakes share an international border between the U.S. and Canada. The Great Lakes basin is the most ecologically diverse freshwater system of its kind.

What is Mercury?

Mercury is a naturally occurring element that is found in cinnabar, 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 in the water, microorganisms take mercury 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 or fish from the Great Lakes. Mercury poisoning has 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.


Joint efforts to reduce Mercury

Since 1972 the U.S. and Canada have entered into joint agreements designed to reduce or rid the Great Lakes of persistent toxic substances including mercury. One of the most notable achievements is the Clean Water Act which is regulated by the Environmental Protection Agency (EPA) and has developed water quality criteria 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. Additionally, the U.S. has 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 thermometers 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.

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