Questions and Answers About Eating Fish

Crappie are a fine table fare that can be eaten by all at least once a week.

• What pollutants build up in Wisconsin´s fish?
• Why should we be concerned about contaminants in fish?
• What is mercury? How does it get into fish?
• What about PCBs?
• How do PCBs and mercury differ?
• Who is most at risk?
• Do we have to stop eating fish?
• I've eaten fish. What is going to happen to me or my children?
• Are fish bought from grocers contaminated too? How about fish from restaurants?
• What fish have been tested?
• Can I swim in waters with an advisory?
• What is being done to reduce contamination of Wisconsin´s fish?
• Can I eat fish from water containing blue-green algae?

What pollutants build up in Wisconsin´s fish?

Mercury and polychlorinated biphenyls (PCBs) are the main pollutants that build up in fish from Wisconsin’s waters. Because these pollutants also accumulate in people who eat fish and may adversely affect health, advice is issued by health officials on how much fish may be safely eaten.

PCBs and mercury differ in where they come from, how they accumulate in fish tissue, and how they affect human health. In addition, contaminants like dioxin and perflourooctane sulfonate (PFOS) require fish consumption advice at a few locations. Other contaminants, like DDT and dieldrin, have declined since earlier years and no longer require consumption advice to be issued.

Why should we be concerned about contaminants in fish?

People who frequently eat fish high in contaminants, like mercury and PCB’s, can accumulate levels that may harm their health. Infants and children of women who eat a lot of fish may have lower birth weights, delayed development and impaired learning ability. These pollutants can also harm adults by affecting reproductive function and cardiovascular health, immune and nervous systems, and increase risk of cancer.

The Wisconsin Departments of Natural Resources and Health Services advise people about the number of meals and species they can safely eat. By following the recommendations, known as fish consumption advice, Wisconsin residents and visitors can continue to enjoy the fish they catch and benefit from this low-fat, low-cost source of nutrition, while reducing their exposure to these pollutants.

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What is mercury? How does it get into fish?

Mercury is an element that occurs in rocks and soils naturally. Mercury is released to the atmosphere when power plants burn coal, from some chemical manufacturing plants and incinerators, and when mercury containing products are not disposed of properly. When mercury is released into the air, it can travel long distances and be deposited on land and directly into water. Mercury is changed to a form, methylmercury, which builds up in fish and the animals and birds that eat fish. Mercury reaches higher concentrations in long-lived species and species of fish that eat other fish, like walleye.

What about PCBs?

PCBs are a group of man-made chemicals used in a variety of industries. They were used in carbonless copy paper, electrical transformers and as cutting oils and hydraulic fluids. Manufacture of PCBs was banned in the US in 1977. PCBs remain in the environment because they are resistant to breakdown. Where PCBs were discharged, PCBs cling to sediments and, and like mercury, also build up in fish and animals and birds that eat fish. PCBs reach higher concentrations in older, longer lived, fattier species of fish, like carp and great lakes trout and salmon.

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How do PCBs and mercury differ?

PCBs are generally stored in the fat of fish, so you can reduce PCB levels in fish you eat by trimming away the fatty areas and properly cooking your fish. However, mercury is stored throughout the fish including the muscle or fillet. Cooking preparation and heat does not reduce mercury levels.

In humans, the blood carries mercury to the brain and other tissues. You can prevent mercury from building up in your body by choosing species of fish with low mercury concentrations and spacing your fish meals out. Mercury can be eliminated slowly over time. In comparison, PCBs are stored in body fat and remain there for many years. Because PCBs build up in your body over time, it's important to reduce your lifetime exposure to PCBs by avoiding fish from locations with high concentrations of PCBs.

High concentrations of PCBs are most often associated with industrialized river systems and the Great Lakes. While mercury is found in fish from most waters of the state, high mercury concentrations are most typically found in acidic, darkly stained lakes of northern Wisconsin. Our fish consumption advice provides a list of waters along with recommended meal frequencies that vary with the species and size of the fish.

Who is most at risk?

Fetuses and babies are most at risk because their developing nervous systems are much more sensitive to mercury compared to adults' nervous systems. An estimated 60,000 children born each year in the United States are at risk of suffering neurological and learning problems because their mothers eat large amounts of mercury-contaminated fish and seafood during their pregnancy. However, fish is good food and can give your child a healthy start if you eat a variety of fish that are low in mercury and other contaminants.

Do we have to stop eating fish?

No. Continue to enjoy eating fish. fish is low in saturated fat and high in protein. Fish can be a good source of beneficial fatty acids. The nutritional benefits outweigh the potential health risks as long you follow advice for the number of meals and species you can safely eat.

If you eat a lot of fish, you can lower your exposure to pollutants by eating small fish such as perch and bluegill or smaller sizes of predator fish. It's safe to catch and eat fish from most of Wisconsin’s lakes and rivers so long as you follow the safe eating guidelines. Studies suggest that regularly (1 to 2 servings per week) including modest amounts of fish and shellfish in your diet can benefit your health. Little additional benefit is obtained by eating more than 1 to 2 servings per week.

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I've eaten fish. What is going to happen to me or my children?

The risks to you and your children’s health from eating a few meals of contaminated fish are relatively small. Most people do not eat fish frequently enough to cause a problem. In the future, use the fish advisory as a guide for how much fish to consume.

Are fish bought from grocers contaminated too? How about fish from restaurants?

Most ocean fish you'll find at the store - species such as pollock, shrimp, and salmon - have very low levels of mercury. Some ocean fish do have high concentrations of mercury. The U.S. Food and Drug Administration (FDA) [exit DNR] recommends that pregnant women and those planning to get pregnant not eat swordfish, shark, king mackerel and tilefish because these species contain high levels of mercury. FDA has found that women of childbearing age can safely consume up to 12 ounces of fish per week (2 average meals per week). Wisconsin fish fry typically is cod, haddock, or perch, which are among the safest species of fish to eat.

You have little cause for concern if you eat or buy a variety of commercial fish or eat less than one meal per week of fish. Regardless of whether the fish you eat is store-bought or caught from Wisconsin waters, monitor the amount and species of fish you are eating and follow the state's fish consumption advisory to decide which are safest.

What fish have been tested?

Wisconsin has more than 15,000 lakes and 40,000 miles of rivers. The DNR has been able to test fish from over 1,600 sites since the 1970s, focusing efforts on popular lakes and rivers and those near industrial centers. Because of the large amount of data we've gathered, we know how much mercury is generally found in different fish species. With that information, we determined the consumption advice for how many meals of certain species people can safely eat to reduce their risk of exposure to mercury. In addition, some waters have more restrictive advice due to higher concentrations of mercury or PCBs.

Can I swim in waters with an advisory?

The amount of contaminants you would inadvertently ingest as a result of swimming in waters contaminated with environmental toxins is insignificant. However, ingesting surface waters should be avoided unless first properly treated.

What is being done to reduce contamination of Wisconsin´s fish?

Wisconsin has taken many actions to reduce mercury emissions and to clean up PCBs which remain in sediments of some waters of the states. For further information, please see DNR’s mercury website or sediment management websites.

Can I eat fish from water containing blue-green algae?

Some blue-green algal toxins have been shown to accumulate in the tissues of fish and shellfish, particularly in the viscera (liver, kidney, etc.). Whether or not the accumulation levels are sufficient to pose a risk to humans is uncertain, although it would depend in part on the levels of consumption and on the severity of the blue-green algae blooms where the fish or shellfish were caught or collected.

The World Health Organization advises that people who choose to eat fish taken from water where a blue-green algae bloom is present eat such fish in moderation and avoid eating the guts of the fish, where accumulation of toxins may be greatest. Also, take care to not cut into organs when filleting the fish and rinse the fillets with clean water to remove any liquids from the guts or organs before freezing or cooking. Learn more about blue-green alage.

For more information on contaminants in fish, please contact:
Candy Schrank, Aquatic Toxicologist
(608) 267-7614

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