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Bioaccumulation of Mercury

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. Methylmercury in the water and sediment is taken up by tiny animals and plants known as plankton.
  2. Small fishes 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.

The State of Vermont Fish Contaminant Monitoring Program has been monitoring the levels of mercury in fish tissue since 1987. Measureable concentrations have been observed in 95% of the samples collected from lakes and rivers across the state. The Vermont Department of Health-- off-site link -- has issued a fish consumption advisory which recommends consumption levels based on fish species and special advisories for certain water bodies. The advisory is also more protective of women of childbearing age and children under age 6.


Mercury Education & Reduction Campaign    103 South Main Street    Waterbury, VT 05671    802-241-3455
MERC is a program of the Vermont Department of Environmental Conservation

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