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Fish, in general, are:
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Mercury is a metal that comes from natural sources, mining, and air fallout from burning coal and other fuels. The Northern California Coast Range, where Clear Lake is located, is naturally rich in mercury and other ores. The Sulphur Bank Mercury Mine, located on the shore of Clear Lake, has caused mercury contamination of the lake sediments
Once mercury gets into the water, it settles to the bottom where bacteria in the mud or sand change it to the organic form methylmercury. Methylmercury, a more toxic form of mercury, gets into fish and shellfish through the food they eat. It is passed up the food chain from small plants and animals to larger, older fish, where it builds up.
For more information visit the Environmental Health Mercury in Fish page.
Mercury from volcanoes, coal burning power plants, and mines gets into the water. In the water, the mercury is turned into a form that can be absorbed by fish. Small fish become contaminated with mercury, which are then eaten by larger fish. The largest fish have more mercury because they eat lots of smaller fish and they tend to live longer, so they build up more mercury in their bodies over time. Mercury attaches to the protein in the muscle, or fillet, of fish, and cannot be removed by cooking or cleaning the fish.
When exposed to high amounts of mercury, children and babies may have problems learning, paying attention, remembering things, walking and talking. A developing fetus (or unborn baby), babies, children and teenagers are more vulnerable to the harms of mercury than adults because their brains are still developing, and it takes smaller amounts of mercury to cause health problems. During pregnancy, mercury can pass from a mother to the fetus. In smaller amounts, it can also pass into breast milk. Older children are also vulnerable to mercury because their brains are still developing.
The brain and nervous system are most affected by mercury. Adults exposed to high amounts of mercury may have problems with headaches, numbness and tingling, loss of balance, difficultly walking, shaking, difficulty hearing, and changes in vision, among other problems. It takes about 70 days for the amount of mercury in your body to decrease by half, once you stop eating high-mercury fish. A person can reduce the amount of mercury in their body substantially by limiting consumption of fish for three months or more.
In order to protect families from the harms of mercury from fish, it is important to check local fish advisory when eating fish caught in California. A fish advisory provides information in order to make healthy choices on eating fish caught in the state, and will help identify fish to eat that are low in mercury and other chemicals.
Fish advisories can be found on:
Fish is a healthy source of protein. The best way to limit one's exposure to mercury is to choose fish with lower levels or to eat smaller portions of mercury-containing fish. Consult advisories to determine which fish are best to eat for pregnant women and children.