Skip to main content

Bioaccumulative and Persistent Chemicals in Fish

The Michigan Department of Health and Human Services’ (MDHHS) fish consumption guidelines found in the Eat Safe Fish (ESF) Guides are the result of the fish we eat being exposed to chemicals that have been released into the environment. The chemicals can build up in their muscle tissue, the part you eat. Many of these chemicals were released into the environment – by accident or on purpose – before we knew the long-term health and environmental problems they can cause.

The chemicals can travel through the air, and they can be carried by rain run-off and storm drains into our lakes, rivers and wetlands. Once in the water, the chemicals sink to the bottom, are absorbed by small aquatic creatures and become a part of the fish food chain. Some of these chemicals are persistent and can stay in the environment, in the fish, and in the human body for a long time.

You can’t see or taste these chemicals. They do not change how clear or dirty the water looks. The only way to know if these chemicals are in the fish is by testing for them in a laboratory.

Bioaccumulation and Biomagnification

Chemicals in the environment can also bioaccumulate in fish. This means that they build up in the fish found in some of Michigan’s lakes and rivers. As these chemicals bioaccumulate in individual fish, they also increase in concentration as you move up the food chain. This process is known as biomagnification.

Biomagnification in Action

Graphic showing the process of biomagnification. First, chemicals end up in lakes and rivers though many routes, like wind, rain run-off and flow from other waterbodies. Next, the chemicals settle into the sediment at the bottom of the lake or river. Small aquatic creatures then absorb some of the chemicals in the water or sediment. These aquatic creatures are eaten by larger fish and those fish are eaten by even larger fish. Each fish collects and stores some of the chemicals in their bodies. Through this food chain, larger fish and older fish are more likely to have higher levels of some chemicals, such as mercury and PCBs, than smaller and younger fish.**

**This trend does not apply to PFOS, which is sometimes found at high levels in smaller fish. Be sure to check the Eat Safe Fish Guides to see if PFOS is a concern for your catch.

Persistent Chemicals

The chemicals found in Michigan fish are also persistent. This means that they stay in our environment for a long time and do not break down easily. Chemicals such as mercury, dioxins, polychlorinated biohenyls (PCBs), perfluorooctane sulfonate (PFOS) and dichloro-diphenyl-trichloroethane (DDT) are all persistent chemicals.

Graphic showing a factory emitting a large amount of pollution, alongside a graphic of the same factory emitting less pollution. Text reads "In the 1970's, before environmental regulations, factories released a lot of persistent chemicals into the environment. Today, many factories have rules about how many chemicals they can release. However, some releases from the past remain in the environment."

If you eat a lot of fish that have these persistent and bioaccumulative chemicals in their bodies, these chemicals can build up and stay in your body too.

Using the Eat Safe Fish Guides

The ESF Guides are designed to protect any person who eats fish from Michigan waterbodies. Using the ESF Guides will keep you from getting too many chemicals in your body at once. Scientists set the limits in the ESF Guides so that you are protected from possible health problems from the chemicals, no matter how long they stay in your body.

Not everyone will get sick from eating too many of these chemicals. The chemicals in the fish won’t make you sick right away. Some people will be fine after years of eating fish with these chemicals in them. Others can have health problems.

You may choose to eat more fish than the ESF Guides recommend. These guidelines are not rules; it is your choice. The ESF Guides make it easy for you and your family to make safer choices and avoid eating too many chemicals in fish.