Chemical levels decline among those who eat Great Lakes fish.

Jan 13, 2009

Knobeloch L, M Turyk, P Imm, C Schrank, and H Anderson. 2008. Temporal changes in PCB and DDE levels among a cohort of frequent and infrequent consumers of Great Lakes sportfish. Environmental Research 109:66-72.

People fishing in Lake Erie.

 People in the Great Lakes region -- long known for its high levels of contamination -- are carrying around less of some of the most dangerous and harmful chemicals found there. Thirty years after the national bans on PCBs and DDT, researchers find lower chemical body burdens, even in those who catch and eat sport fish.



Long-lived, toxic chemicals -- either banned or with limited use -- continue to pollute people and the environment. The pesticide DDT was widely used in agriculture and insect control from the 1950s to the 1970s. The fire resistant class of oils called polychlorinated biphenyls (PCBs) were widely used in transistors, capacitors and other electronics equipment during the same decades. The United States banned the use of DDT in 1973 and halted production of PCBs in 1977.

The compounds, however,  remain in the environment. The chemicals can last for years -- or even decades -- in soil and lake sediment. Often, DDT breaks down into DDE, another extremely persistent, toxic compound. DDT, DDE and PCBs accumulate in fat, and most Americans have detectable levels in their bodies.

The main continuing source of human exposure to DDT, DDE and PCBs is through diet, particularly meat, dairy products and fish. 

Levels of these contaminants in the Great Lakes have declined considerably since the products were banned. The contamination varies by lake and by species -- longer lived, more fatty fish like lake trout and catfish have high concentrations  compared to shorter lived Chinook salmon and perch.

DDT and PCBs are found in the water at low concentrations and more so in sediments and soils. Even so, wildlife and people can have higher levels because the chemicals bioaccumulate and concentrate in fat and tissues as they move up the food chain from animal to animal.

DDT, DDE and PCBs are associated with increased risk of cancer, reproductive problems, developmental delays and disruption of hormone function.

Great Lakes fish advisories list which fish have the highest levels of contaminants. In general, consumers are told to eat fewer meals per week, eat smaller fish, trim off the fat and avoid eating fish skin. Children and women who are pregnant, who may become pregnant or who are breastfeeding should avoid eating fish with high levels of contaminants. 


What did they do?

Scientists from Wisconsin  measured DDE (a breakdown product of DDT) and PCBs in the blood of 293 men and women from 1994 to 1995 and again between 2001 and 2005. The average follow-up time between the first and second blood measurement was almost 10 years. The researchers targeted men and women who sport fish by inviting anglers and charter boat captains to participate. The study also enrolled people with low fish consumption who lived in the same neighborhoods as people who fished.

What did they find?

Over an average of almost 10 years, DDE levels declined in 89% of the study's participants, and PCBs declined in 80%.

Overall, DDE concentrations declined by 43%, or about 5% per year, and PCB concentrations decreased by 33%, or 4% per year.

People who decreased the amount of fish they ate during the study period showed the largest declines. But, decreases were also seen among those who kept their fish consumption steady or even increased their fish intake.

The highest DDE and PCB concentrations were found among older males who fished.

What does it mean?

People living in the Great Lakes region have lower levels of DDT, PCBs and other pollutants than they did a decade ago. Even those who continue to eat sport fish saw a decline in blood levels.

This study is important because it is one of just a few that shows in people how levels of some of the most persistent chemicals change over time. The large study population adds to the strength of the analysis.

Although levels of these chemicals are declining, they are still higher among sports fishermen than among the general population. Sport fishing is an extremely popular recreational activity in the Great Lakes region with more than 1 million fishing licenses issued each year.

Lower PCB levels in both frequent and nonfrequent sport fish eaters could be due to lower levels of the chemicals in the environment and practically no work or home exposure, suggest the authors.

The decline may also reflect a change in the species caught and eaten from Lake Michigan. The majority of the participants fished mostly from that lake, and the fisheries has changed from predominately lake trout to a mix of trout, Chinook salmon and perch.

DDE and PCB levels in Great Lakes fish declined dramatically in the 1970s and 1980s following the ban of the chemicals. Levels stabilized since the mid 1980s. An older study of Great Lake fish eaters and non-fish eaters found that DDT levels had decreased between 1982 and 1989, but PCB levels had decreased very little.

DDT and PCBs continue to persist in the environment and bioaccumulate in the food chain. Levels of both chemicals are particularly high in fatty fish from the industrial Great Lakes region. Both are suspected carcinogens that may also disrupt hormone function, reproduction, the immune system and brain development.

The study highlights how long hazardous chemicals remain in the environment and "underscores the incredible persistence of these chemicals." Even banned, the compounds do not just disappear but continue to pollute water, sediment, food sources, wildlife and people.

Even with this seemingly good news, the authors report that the "majority of participants in our study continue to have detectable levels of PCBs as well as DDE in their blood."

The long term legacies of these chemicals indicate more effort may be needed to develop less toxic materials, possibly through the emerging field of green chemistry,  that do the job with a lower environmental and health cost.


Hagmar,L, E Wallin, B Vessby, BAG Jonsson, A Bergman and L Rylander. 2006. Intra-individual variations and time trends 1991–2001 in human serum levels of PCB, DDE and hexachlorobenzene. Chemosphere 64:1507–1513.

Michigan Department of Community Health. 2008 Michigan Family Fish Consumption Guide. (PDF).

Sweeney,AM, E Symanski, KD Burau, JK Young, HEB Humphrey and MA Smith. 2001. Changes in serum PBB and PCB levels over time among women of
varying ages at exposure
. Environmental Research 86:128–139.

US Environmental Protection Agency. Fish advisories.

US Environmental Protection Agency. Great Lakes National Program Office. Human Health and the Great Lakes.




Pollution in Great Lakes fish