How Mercury Gets Into Fish
Most of the mercury that contaminates fish comes from household and industrial waste that is incinerated or released during the burning of coal and other fossil fuels. Products containing mercury that are improperly thrown in the garbage or washed down drains end up in landfills, incinerators, or sewage treatment facilities. The mercury then leaches into the ground and water. Once mercury enters the water and soil, it is naturally converted to methylymercury by bacteria. In water, the bacteria are eaten by plankton and other small creatures, which in turn are eaten by small fish, then larger fish. Mercury doesn't easily leave the body of an organism, so the amount of mercury builds up in species as they go up the food chain in a process called bioaccumulation (PDF). Larger, older fish accumulate more contaminants than smaller, younger fish.
How Other Contaminants Get Into Fish
Toxic contaminants end up in our state's waterbodies in different ways. Industrial and municipal discharges, agricultural practices, and storm water runoff can all put harmful substances into the water. Rain can also wash chemicals from the land or air into streams, rivers, lakes, and Puget Sound. Fish absorb contaminants such as PCBs, PBDEs, dioxins, and chlorinated pesticides from water, sediments, and the food they eat. In contaminated areas, bottom-dwelling fish are especially likely to have high levels of these chemicals because these substances settle to the bottom where the fish feed.
Health Risks of Eating Contaminated Fish
Contaminants can build up in your body over time and may result in health problems. It can take 5 years or more for women in their childbearing years to rid their bodies of PCBs, and 6-12 months to significantly reduce their mercury levels. Mercury, PCBs, and other contaminants can be passed on to a developing fetus through the placenta.
Mercury related health problems are most severe for the developing fetus and young child. Babies born to mothers who have a lot of mercury in their bodies may develop more slowly and have problems learning. It is believed that infants and children are more susceptible to the effects of mercury because their nervous systems continue developing until adolescence. In adults, mercury can lead to problems of the central nervous system and possible adverse effects on the cardiovascular system.
PCBs are linked to infant development problems in children whose mothers were exposed to PCBs before becoming pregnant. PCBs can cause changes in human blood, liver, and immune functions of adults.
How To Reduce Your Exposure to Contaminants in Fish
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Eat a variety of fish that are low in contaminants. Follow our healthy fish guide when choosing seafood at the store or restaurant.
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Follow statewide mercury advisories for certain store-bought and sport-caught fish - this is especially important for women who are or might become pregnant, nursing mothers, and young children.
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Check local fish consumption advisories before you go fishing in Washington waters.
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Eat smaller, younger fish.
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Avoid eating the skin and fat on fish. See our tips on preparing and cooking fish.
Health Benefits of Fish
Fish is nutritious and beneficial to your health. Fish is low in saturated fat and a good source of protein, vitamins, minerals, and omega-3 fatty acids, which are great for your heart, brain, and overall health. Eat a variety of fish that are low in mercury and other contaminants and follow the steps for reducing your exposure to contaminants in fish to assure you gain the health benefits from fish. Unfortunately, contaminants are in most foods, so avoiding fish and replacing it with other protein sources like meat or poultry will not eliminate your exposure to contaminants.
Eating Fish When Pregnant or Breastfeeding
During your pregnancy is a very important time to eat fish. Remember to avoid eating fish high in mercury and follow the steps for reducing your exposure to contaminants in fish. Breastfeeding provides your baby with health benefits that will last a lifetime. The benefits of breastfeeding outweigh any risks that your baby may receive through breast milk. The key is to continue choosing fish low in mercury and other contaminants so you and your child gain the benefits of fish. The health benefits of fish are important for you, and your child's development. See our fish advice for women and children.
Reducing Contaminants When Cooking
It may be possible to reduce contaminants by preparing and cooking fish a certain way but it depends on the type of contaminant. Contaminants such as PCBs and DDT concentrate in the fat of fish. These contaminants can be reduced by up to 50% by preparing and cooking fish properly. Cut off the skin and fat before cooking fish. Then broil, grill, or bake it on a rack so the fat drips off the fish. Don't use the drippings for sauces. Fish contaminated with mercury can't be prepared or cooked in a way that reduces the mercury. Mercury is stored in the muscle tissue (the meat of the fish).
Choose Light Tuna Over White Tuna
Choose "light tuna" over "white tuna." Our study revealed that mercury levels in canned light tuna were three times lower than those in canned white (albacore) tuna. Albacore tuna is also called white tuna. There does not appear to be much difference in mercury levels between solid and chunk tuna, or between tuna packed in water versus oil. Our canned tuna advice is part of the statewide fish consumption advisory for mercury, which should be followed by women who are or might become pregnant, nursing mothers, and young children.
Salmon
Most species of salmon have very low levels of mercury and other contaminants and are safe to eat. See our healthy fish guide for smart salmon choices.
How To Keep Contaminants From Getting Into Fish
To keep contaminants from getting into fish you have to reduce toxic chemicals getting into the environment. See the Department of Ecology's tips on reducing toxic threats.
What the State is Doing
Washington State's goal is to reduce and phase-out persistent, bioaccumulative, and toxic chemicals such as mercury, PCBs, DDT, and dioxins which threaten human health and the health of the environment. Learn more about Ecology's initiative to reduce persistent, bioaccumulative toxics.
Clean water is essential to have healthy fish. We work closely with the Department of Ecology to assess contaminants in fish. Ecology identifies and monitors toxic chemicals found in aquatic environments and identifies actions that can be taken to reduce these chemicals. See Ecology's reducing toxic substances in our environment to find out what Washington State is doing.
More Information on Contaminants
Content Source: Fish Advisories Program