Great Lakes fish eaters less contaminated than a decade ago

Anglers who ate Great Lakes fish have 33 percent fewer PCBs and 43 percent less DDT in their bodies than they did a decade ago, largely because they changed their diet and switched to less contaminated fish, according to a study by Wisconsin researchers.

The scientists compared blood drawn from people in 1994-1995 with blood from the same people drawn roughly nine years later. Most of the 293 men and women tested were sports fishers and boat captains who consumed large amounts of Great Lakes fish.

One reason for the decline “is that your body excretes these chemicals over time as they slowly get metabolized,” said Lynda Knobeloch, study leader and senior toxicologist at the Wisconsin Department of Health Services. “The other is that exposure levels are much, much lower than what they were 30 years ago.”

Polychlorinated biphenyls, or PCBs—industrial compounds used largely to insulate electrical transformers—and the pesticide DDT were banned in the United States in the 1970s. Yet they are extremely slow to break down in the environment, which means they accumulate and persist in lake sediment and in the bodies of animals and people.

Concentrations of PCBs in the blood of the people studied declined on average 3.5 percent per year over the nine-year period. Levels of DDE, a metabolite of DDT, declined even more, 4.6 percent per year, according to the report, published last month in the journal Environmental Research.

The drop in the chemicals was found in both frequent and non-frequent fish consumers. People age 30 and below tended to have far lower concentrations than people in their 50s, said Knobeloch.

Changes in consumption of fish harvested from Lake Michigan, the predominant lake used by people in the study, played a key role in the findings.

“Many of the people who fished Lake Michigan changed the preference of the fish they were eating,” said Candy Schrank, environmental toxicologist at the Wisconsin Department of Natural Resources. “They moved from eating lake trout in the earlier years, which are a fattier, more polluted fish and switched to cleaner fish,” such as salmon and perch.

Some of the decline in people’s exposure likely can be attributed to dropping levels of PCBs and DDT in the Great Lakes environment. But the big drop in environmental levels came before 1990 and has since leveled off, scientists say. Many fish in the lakes, particularly around hot spots such as harbors, still contain levels that exceed federal health guidelines.

“The majority of participants in our study continue to have detectable levels of PCBs as well as DDE in their blood,” the report says.

PCBs are carcinogenic and have neurological effects on children exposed in the womb. Mothers who ate high levels of PCB-contaminated fish from Lake Michigan gave birth to children with smaller heads and lower weights, according to a 1991 study by Joseph and Sandra Jacobson of Wayne State University.

As these children grew up, that early exposure to the compounds impaired mental skills and reduced their IQs, according to the Jacobsons’ research.

Other research concludes that PCBs reduce mental skills later in life, too. Sport fishermen who consume large amounts of fish laced with PCB from the Great Lakes showed difficulty memorizing and learning new verbal information in a 2001 study. Many had trouble remembering a story told to them 30 minutes earlier.

In addition to benefiting human health, reductions in pollutants are good for Great Lakes commercial and sport fisheries, said Thomas Goniea, fishery biologist with the Michigan Department of Natural Resources. Demand for some fisheries has declined because of fish tainted with mercury and PCBs, he said.

Over 18 million pounds of commercial fish were harvested from the lakes in 2006, generating close to $15 million for the region a year, according to a U.S. Geological Survey annual fishing survey.

This story first appeared on Environmental Health News.