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Mercury in NH's Freshwater Fish


What is Mercury?

Mercury is a naturally occurring metal that has many forms, including elemental mercury used thermometers, inorganic mercury used in certain paints and pesticides,and organic mercury, which is sometimes found in fish.

How does mercury get into freshwater fish?

Small microorganisms living in the sediments and water convert inorganic mercury into the more toxic organic form. Mercury is part of the concern because it can accumulate in fish at levels many times greater than in the surrounding water. Small fish and other organisms living in the water can take up mercury. When larger fish eat the smaller fish, much of the mercury present in the small fish will be absorbed and stored in their bodies. Therefore, large fish at the top of the food chain, like bass and pickerel, can collect a relatively large amount of mercury.

How can mercury affect my health?

Mercury has no purpose in the human body and when taken into the body may pose a danger to human health. The low levels of mercury found in New Hampshire fish do not cause immediate sickness. Mercury can, however, build up in the body over time from ingesting contaminated fish. Exposure to high levels of mercury can permanently damage the brain, kidneys, and developing fetus.

Young Children and Unborn Children

Children are more sensitive to mercury because their nervous systems are still developing and more of it passes into their brains where it interferes with normal development. A pregnant woman may pass mercury to her unborn child through the placenta or a breastfeeding mother may pass mercury to a nursing child through the breast milk. Typical adverse effects that have been observed in children exposed to elevated levels of mercury include delayed development, for example, a delay in the time it takes before a child begins to walk.

General Population

The nervous system is very sensitive to all forms of mercury. In the general population, the health effects associated with ingesting elevated amounts of organic mercury include tingling or numbness in the hands, feet or around the mouth. Vision and hearing may also be affected.

How do we know mercury is a problem in freshwater fish?

Since 1990 more than 500 fish have been sampled and tested from approximately 100 lakes, ponds and rivers. Sample results have shown that levels of mercury found in freshwater fish may be potentially harmful.

There are typically only a small number of fish -usually less than five per lake- that are sampled from any given lake making it difficult to conduct a specific assessment on any given water body. Because a wide range of water bodies were sampled across the entire slate, these results are anticipated to provide a fairly representative picture of fish mercury levels throughout New Hampshire. Sample results have shown elevated fish mercury levels to occur in lakes/ponds located in remote
pristine areas as well as more developed areas which indicates the problem is more wide spread and not just limited lo certain locally impacted water bodies.

If fish may be contaminated should I stop eating freshwater fish?

The public is encouraged to continue eating fish as part of a healthy diet. Fish are high in protein and low in saturated fat and cholesterol. A diet low in fat contains fewer calories. Eating fish may play a part in reducing the risk of certain cancers and heart disease. To reduce the exposure to mercury, the Department of Health and Human Services recommends that you limit the amount of freshwater fish in your diet according to the guidlines listed below:

Woman of childbearing age - One 8oz meal per month
Children under six years of age - One 8oz meal per month
All other consumers - Four 8oz meals per month