Consuming fish can provide several health benefits. Fish consumers should be aware that there may be chemicals in the environment that can build up inside fish and may cause future health problems. The Michigan Department of Environment, Great Lakes, and Energy (EGLE) collects fish from all over Michigan to monitor for these chemicals.

These data are used by the Michigan Department of Health and Human Services (MDHHS) to issue fish consumption advisories, which are listed in their Eat Safe Fish guides. These include mercury, polychlorinated biphenyls (PCB), chlorinated pesticides (e.g., Dichlorodiphenyltrichloroethane [DDT]), dioxins, and per- and polyfluoroalkyl substances (PFAS).

More information on potential health risks from consuming fish with these chemicals can be found in MDHHS’ Eat Safe Fish FAQs.

In Michigan, mercury is the most common contaminant in fish. While mercury is a naturally occurring element, certain human activities (e.g., mining and fossil fuel combustion) have resulted in global mercury pollution. Atmospheric mercury enters aquatic ecosystems through precipitation where it is converted into methylmercury and becomes available to the aquatic food web. Mercury is both a bioaccumulative contaminant (meaning it will be found at higher concentrations in the fish compared to the surrounding water) and a biomagnifying contaminant (meaning it will be found at higher concentrations in species of fish that feed higher on the food chain and eat other fish [e.g., Walleye] compared to species that feed lower on the food chain on aquatic macroinvertebrates [e.g., Bluegill]). Mercury tends to accumulate more in the muscle of fish than in the fat, meaning that it cannot be removed during filleting and/or cooking. 

For more information check out our Mercury webpage.

PFAS are a group of synthetic chemicals used in the manufacturing of many products including fire-fighting foam, stain repellants, non-stick cookware, and many others. Many PFAS do not break down in the environment and can remain in the water and lake sediments for decades where they become available to the aquatic food web. Similar to mercury, certain PFAS (e.g., perfluorooctane sulfonate [PFOS]) accumulate in the muscle of the fish and cannot be removed during filleting and/or cooking.

More information about PFAS can be found on the Michigan PFAS Action and Response Team (MPART) page.

Other legacy contaminants are chemicals once used in the United States but then were either discontinued or their use in the United States was banned. Several of these legacy contaminants do not readily break down in the environment and can remain in the water and lake sediments for decades where they become available to the aquatic food web. PCBs are synthetic chemicals that were manufactured domestically for a wide range of industrial and commercial applications until their manufacturing was banned in 1979.

Chlorinated pesticides were used extensively for agricultural pest and mosquito control, including DDT, toxaphene, and chlordane. DDT was a commonly used pesticide for insect control in the United States until it was banned in 1972. Chlordane was primarily used in the United States for termite control and was banned in 1988. Toxaphene was primarily used on cotton crops and was banned in 1990. Dioxins are a group of chemically-related compounds that are mainly byproducts of industrial processes but can form during natural processes such as forest fires and volcanic eruptions. 

More information on dioxins can be found at Michigan.gov/EGLEDioxin. Many of these legacy contaminants build up in the fat of fish; therefore, species that have a higher fat content (e.g., Common Carp, Redhorse Suckers, Lake Trout) tend to have higher concentrations of PCBs, DDT, and dioxins compared to leaner species (e.g., Walleye, Bluegill, Largemouth Bass). 

The majority of the samples submitted by EGLE’s Fish Contaminant Monitoring Program (FCMP) are edible portions (the portion that people eat [e.g., fillets]). These edible portion data are then used to inform the MDHHS’ Eat Safe Fish consumption advisories. EGLE does occasionally test the entire body of fish to determine if water quality is improving; however, these whole fish data are not used for consumption advisory determination.

Every year, EGLE’s FCMP receives federal and state funding to assess contaminants in fish from Michigan’s water bodies. Select water bodies are routinely monitored (every 3 to 5 years) due to data needs in other programs (e.g.,  Areas of Concern Program). Other locations are selected based on several factors including:

1. Funding availability.
2. Information regarding newly discovered contamination sources and/or recent remediation efforts that may have reduced historical contamination.
3. Requests made via EGLE’s Targeted Monitoring Request screening form.

Species are chosen for contaminant monitoring based on several factors including the contaminants of concern in the water body, common species being targeted by anglers using that water body, species present at time of collection, and/or data needs for trend monitoring. Top predator species, such as Walleye or Smallmouth Bass, are commonly selected for testing in water bodies where mercury is the main contaminant driving consumption advisories.

In PCB- or DDT-impacted waters, bottom dwelling species, such as Common Carp or Channel Catfish, or species with a higher fat content, such as Lake Trout, are frequently targeted for contaminant monitoring. Panfish species, such as Bluegill or Black Crappie, are usually selected for contaminant monitoring during PFAS investigations. In many circumstances, EGLE will test multiple species of fish from several trophic levels to allow advisory development to protect several different types of anglers. Unfortunately, not all species from a water body can be tested due to several limitations (e.g., funding).

EGLE uses a variety of methods to collect fish from water bodies for contaminant monitoring including electrofishing, gillnetting, and/or hook and line (i.e., fishing) and does so through obtaining a scientific collectors permit through the Michigan Department of Natural Resources. Electrofishing is the most common technique used by EGLE to collect fish.

Samples collected by EGLE’s FCMP are sent to the MDHHS’ Bureau of Laboratories for chemical analyses. The time it takes to receive results from the laboratory depends on several factors; however, it generally takes between 8 and 12 months to obtain the full set of data for a given sample.

EGLE’s FCMP does not take in samples collected from the general public. Exceptions have been made in the past if EGLE staff were able to observe the fish collection. There are private laboratories that can analyze fish tissue for contaminants. Alternatively, anyone can submit a Targeted Monitoring Request to request analysis of contaminants in fish from many water bodies throughout the state of Michigan.

EGLE's Water Resources Division solicits surface water quality and fish contaminant monitoring recommendations every year, and selects recommendations for monitoring based on merit, existence of historical data, and funding availability. You can visit the Targeted Monitoring Request page to learn more about this process and submit monitoring requests throughout the year.

The majority of water bodies tested by EGLE’s FCMP are public waters. EGLE will test fish from private lakes with multiple lakefront residences if there is a contamination concern. EGLE does not test private ponds that reside within properties owned by a single landowner (e.g., farm ponds).

EGLE’s FCMP implemented a whole fish trend monitoring program in 1990. Under this program, sport fish are collected from fixed stations across the state every three to five years and the entire fish is sent in for contaminant analyses (whole body fish analysis). EGLE staff use these data to determine if contaminant concentrations are increasing, decreasing, or staying the same over time (temporal trend analysis) and compare the trends across areas of the state (spatial trend analysis). These data are not used to determine fish consumption advisories.

Caged fish studies are used by EGLE to determine sources of contamination and/or to evaluate the overall effectiveness of EGLE programs in reducing contaminant levels in Michigan’s water bodies. For these studies, fish are purchased from a hatchery and deployed in stainless steel cages at multiple locations in rivers or across an entire watershed.

The fish are left in the cages for 28 days where they accumulate contaminants through contact with the water. After the deployment, the fish are processed as whole-body samples and sent in for contaminant analysis. EGLE uses the data to determine if contaminant concentrations are elevated at a particular location in the river or watershed (spatial trend analysis) or if concentrations have increased, decreased, or stayed the same compared to a previous caged fish study (temporal trend analysis).

EGLE’s FCMP data are currently stored on an internal database. EGLE does publish fish contaminant data that are used to establish the MDHHS’ fish consumption advisories on the MPART GIS page. This layer is updated annually. Requests for non-publicly available fish contaminant data can be made by reaching out to the FCMP monitoring coordinator. Data requests for research purposes may be subjected to the establishment of a Data Sharing Agreement.