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New Hampshire Department of Environmental Services
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Volunteer Mercury in Fish Sampling Program
What is Mercury and where does it come from?

Mercury is a naturally occurring element that is found in rocks, soils, sediments, and the atmosphere. The element is a relatively stable metal that does not readily react chemically, and will vaporize at relatively low temperatures. Mercury is a potentially serious environmental contaminant that can adversely affect wildlife and humans.

Some natural emissions of mercury are soils, volcanoes, weathering, and forest fires. In addition mercury is emitted through anthropogenic activities, such as burning of municipal waste, and burning of fossil fuels (which is the greatest cause of emission). The mercury in the air then settles into the waters and eventually into the underwater sediment, where bacteria convert the mercury into a form that can enter the food chain. Mercury is then consumed by progressively higher life forms, and bioaccumulates through each consumption. Fish that consume other fish, like bass and pickerel, have the highest mercury levels. Generally the larger and older the fish the higher levels of mercury it will contain. This is why, for species such as bass and pickerel, it is recommended that people only eat fish 12 inches (30 cm.) or less in length.

The mercury problem is not limited to freshwater fish. Although most ocean fish and shellfish have low levels of mercury, with the exception of swordfish and shark, which have very high levels, there are still safe eating guidelines.




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