Contaminants in Top Predator Fish

Background

The Open Lakes Trend Monitoring Program provides data to assess the health of fish and fish-consuming wildlife of the Great Lakes through monitoring of contaminant concentration trends in top predator fish, such as lake trout and walleye, and assessment of the overall effects of toxic chemicals on fish and fish-consuming wildlife. Top predator fish can be used as biological monitors of overall water quality and ecosystem health because contaminant concentrations in fish generally reflect overall contaminant levels in the environment. For example, contaminant concentrations in fish at the top of the food chain reflect contaminant levels in both the surrounding water and in organisms below them in the food chain (Biomagnification). Contaminant concentrations in fish also provide information about risks to organisms in higher trophic levels, such as fish-consuming wildlife.

Program Goals

By monitoring contaminant trends in Great Lakes fish, we can determine whether the Great Lakes basin ecosystem is becoming healthier with regard to chemical contaminants. An increase in contaminant concentrations in top predators indicates a degrading environmental condition, while a decrease in contaminant concentrations in top predators indicates an improving environmental condition. Most importantly, measurement of contaminant concentrations is intended as a means to assess the progress towards the International Joint Commission's goal of safe consumption of fish by all wildlife. Fish-consuming wildlife rely upon fish for the majority of their diet, unlike humans with varied diets, and are therefore extremely susceptible to toxic contaminants in the environment.

Under the 2003-2008 EPA Strategy ( http://www.epa.gov/ocfopage/plan/plan.htm ) and the Government Performance and Results Act (GPRA) the Great Lakes National Program Office (GLNPO) reports the average annual percent decrease in total PCB concentration in whole Great Lakes top predator fish.  The GPRA target goal is a 5% average annual decline.  The most recent analytical results indicate that on average, total PCB concentrations in whole Great Lakes top predator fish have meet or exceeded the target goal since 1990. Clean up efforts, such as the remediation of contaminated sediments and the reduction of PCB loadings to the Great Lakes, need to be continued and enhanced to continue the declining trend.  Based on Lake Michigan data, current total PCB concentrations in whole lake trout are approximately 8 times the wildlife protection value (0.16 ppm). 

Total PCB Average Annual Percent Reductions in Whole Top Predator Fish

Methods

The program funds and coordinates collection and analysis of a variety of chemicals in lake trout from the open waters of Lakes Superior, Huron, Michigan and Ontario. Walleye are collected in Lake Erie due to the limited number of lake trout and the difficulty in collecting them. Fish samples are collected in the fall of the year, using fish of similar size to reduce the impact of size variation on contaminant trend data. Fish samples are then analyzed for several different contaminants, including PCBs, DDT, toxaphene, chlordanes, nonachlors, and other organochlorine compounds. Whole fish, including parts not usually eaten by humans, such as the liver and bones, are analyzed because wildlife consume whole fish.

Contaminants Measured

Bioaccumulation and Biomagnification

Certain human-made organic chemicals present in the Great Lakes biologically accumulate, or bioaccumulate, in resident organisms. Even though these chemicals may be present in the water in only very low concentrations, organisms such as phytoplankton bioaccumulate these toxic chemicals at much higher concentrations than are found in the water. As phytoplankton are eaten by zooplankton and small fish, the toxic chemicals are further concentrated in the bodies of zooplankton and small fish. Bioaccumulation occurs at each step of the food chain, resulting in top predators, such as lake trout and walleye, amassing high concentrations of contaminants. This process of increasing concentration of contaminants through the food chain is known as biomagnification. 

Effects of contamination on wildlife

Chemical contaminants can be acutely toxic in relatively small amounts and harmful through long-term (chronic) exposure, even in small concentrations. Adverse effects of chemical contaminants on aquatic and wildlife species, such as cross-bills and egg-shell thinning in birds and tumors in fish, have been widely observed. In addition, there is also evidence to suggest that PCBs and other contaminants in the Great Lakes may inhibit or limit the reproduction of certain fish and wildlife species. For example, although greatly recovered from their decline in the 1960s, shoreline populations of bald eagles are experiencing limited reproductive success relative to inland populations in the Great Lakes basin. These reproductive problems are most likely due to higher contaminant levels in the diet of the shoreline eagle populations.

Endpoints

The Great Lakes Fish Monitoring Program (GLFMP) uses several endpoints to assess the health of top predator fish in the Great Lakes.  The Great Lakes Binational Toxic Strategy (GLBTS) between the United States and Canada states that contaminants in the Great Lakes should be moving “…toward the goal of virtual elimination of persistent toxic substances resulting from human activity, particularly those which bioaccumulate, from the Great Lakes basin, so as to protect and ensure health and integrity of the Great Lakes ecosystem.”  The Great Lakes Water Quality Agreement (GLWQA) expresses the commitment of Canada and the United States to restore and maintain the chemical, physical and biological integrity of the Great Lakes Basin Ecosystem and includes a number of objectives and guidelines to achieve these goals.  The GLWQA criteria for PCBs states that, “The concentration of total polychlorinated biphenyls in fish tissues (whole fish, calculated on a wet weight basis), should not exceed 0.1 micrograms per gram (or ppm) for the protection of birds and animals which consume fish”, the GLWQA criteria or DDT is 1.0 ppm.  The United States Environmental Protection Agency (U.S. EPA) has developed wildlife protection values for fish tissue concentrations protective of wildlife. U.S. EPA is reasonably confident that contaminant concentrations below these values will not adversely affect wildlife.  The wildlife protection value for PCBs is 0.16 ppm (U.S. EPA, 1997).

Contaminant concentrations in the Great Lakes are decreasing.  However, the rate of decrease varies from lake to lake due to differences in lake size and historical contaminant input.  In addition, direct comparison of concentrations across lakes is not possible because the GLFMP was designed to analyze fish of a similar size, rather than a similar age, and each lake’s fish have a different growth rate.  The age of fish greatly affects the bioaccumlulation of contaminants.  Because the relationship between age and length varies from lake to lake, only general chemical concentration patterns can be observed.  This is especially true for Lake Erie, where walleye are collected as the top predator fish instated of lake trout.

Top predator fish are collected from each lake on an annual basis. Each lake was assigned two different collection sites and fish are collected from one lake site in even years and the other lake site in odd years. Only even year data are reported here as they comprise the most statically robust data set. Collection sites are listed below:

Contaminant Concentrations in Top Predator Fish by Lake

Total PCBs

The above graph illustrates that PCB concentrations in Great Lakes top predator fish are declining. However, it is important to note that the concentrations of this contaminant remain above the wildlife protection value of 0.16 ppm and the GLWQA criteria of 0.1 ppm. PCB fish advisories remain in place for all 5 of the Great Lakes. 

Total DDT concentrations in Great Lakes top predator fish are also declining.  However, it is important to note that the concentrations of this contaminant remain above the GLWQA criteria of 1.0 ppm.  There is no wildlife protection value for total DDT because the PCB value is more protective.

Lake by Lake Assessments

Lake Michigan – Concentrations of ∑ PCBs and ∑ DDT are declining.  ∑ PCB levels remain above GLWQA criteria and ∑ DDT levels remains below.  Food web changes are critical to Lake Michigan contaminant concentrations.  Aquatic invasive species such as Asian carp are also of major concern to Lake Michigan due to the connection of Chicago Sanitary and Ship Canal and the danger the carp pose to the food web.

Lake Superior – Concentrations of ∑ PCBs show little change, ∑ DDT shows fluctuating concentrations, while mercury concentrations continue to decline.  ∑ PCB concentrations remain above GLWQA criteria while ∑ DDT and mercury remain below.  Contaminants in Lake Superior are typically atmospherically-derived.  The dynamics of Lake Superior allow for the retention of contaminants much longer than in any other Great Lake.

Lake Huron - Both ∑ PCBs and DDT show general declines in concentrations while mercury displays a flux in concentration.  ∑ PCB concentrations remain above GLWQA criteria while ∑ DDT and mercury remain below.  Contaminant loading to Saginaw Bay continues to be reflected in fish tissue contaminant levels.

Lake Erie – ∑ PCBs and DDT concentrations show a pattern of annual increases linked to changes in invasive species populations, such as zebra and quagga mussels.  Aquatic invasive species are of major concern to Lake Erie.  ∑ PCB concentrations remain above GLWQA criteria while ∑ DDT and mercury remain below.

Lake Ontario – Both ∑ PCBs and DDT concentrations show a pattern of decline while mercury concentrations show little change.  ∑ PCB concentrations remain above GLWQA criteria while ∑ DDT and mercury remain below.  Historic point sources of mirex and OCS have resulted in higher concentrations in Lake Ontario than any other Great Lake.  Contaminants of emerging concern, such as PBDEs and PFOS, continue to raise alarm in Lake Ontario.

Acknowledgements

Carlson, D.L., and Swackhamer D.L.  2006.  Results from the U.S. Great Lakes Fish Monitoring Program and Effects of Lake Processes on Contaminant Concentrations.  Journal of Great Lakes Research.  32 (2): 370 – 385.

DeVault, D.S., Hesselberg, R., Rodgers, P.W., and Feist, T.J., 1996. Contaminant Trends in Lake Trout and Walleye from the Laurentian Great Lakes. J. Great Lakes Res. 22(4): 884-895.