MONDAY, Oct. 29, 2001 (HealthDayNews) -- Falling concentrations of air pollution in the Midwest seem to have a slight vacuum effect on the Great Lakes: the pollutants are being drawn out of the water, say researchers.
Thanks to pollution controls, concentrations of many chemicals in the air have fallen, and when the air is cleaner than the water, pollutants evaporate off the surface of the water, say environmental researchers.
"Think of the lakes as giant lungs that have been sucking in polluted air for the last 50 years," said Keith Puckett, Environment Canada's manager of the IADN. "Now that atmospheric levels of many of these pollutants have dropped below the equilibrium point, the lakes are starting to exhale." The Great Lakes hold one-fifth of the world's supply of fresh water.
Latest figures from the bi-national, U.S.-Canadian Integrated Atmospheric Deposition Network (IADN) show a net release from Lake Ontario alone of about 900 pounds of PCBs (polychlorinated biphenyls) into the air, as well as significant amounts of dieldrin and other pesticides, over the five years from 1992 to 1996. In the same time period, the five Great Lakes combined showed a net decrease of cancer-linked PCBs of roughly 4,500 pounds and a net decrease of nerve-damaging dieldrin of more than 1,800 pounds.
So where are all these chemicals going after the lakes spit them out?
Some of them are disintegrating, but many are simply being redeposited someplace else, explains Melissa Hulting, U.S. program manager for the IADN.
DDT, for instance, hitchhikes on the northbound air currents during the summer months, traveling toward the arctic until cold temperatures disrupt the evaporative cycle and trap them, causing high concentrations near the North Pole. And some of the chemicals are just rained back into the lakes and streams that are the Great Lakes tributaries.
But overall, the net effect is an improvement, Hulting says. "When the lakes exhale, you don't have to hold your breath."
Emily S. Green, director of the Great Lakes program for the Sierra Club, is among those who believe that the news is not all that good.
"This study shows that the Great Lakes are getting cleaner, and that's seen as a success story. I'm not saying it's a bad thing; I'm saying that the problem is moving someplace else," she says.
Green compares the afterlife of these pollutants to radioactivity. "The most toxic ones can cycle around for hundreds of years." She says progress is dependent on further cleanup of landfills and toxic waste dumps
"There are at least 42 toxic sediment sites around the shores of the Great Lakes that, on an annual basis, are contributing things like PCBs to the Great Lakes. Until we clean those up, you'll continue to see high levels of contaminants."
Hulting agrees that there is still a long way to go. She points to one of the most obvious barometers -- the high concentration of pollutants found in many fish in the Great Lakes, making them unsafe for both people and wildlife to eat.
There are currently fish consumption advisories in Lake Michigan, urging women of child-bearing age and children to limit or avoid altogether eating large, long-lived fish like trout, which contain the most toxins. Another research study found that sports fisherman who had eaten significant amounts of contaminated fish from the Great Lakes over long periods of time experienced impairments in certain aspects of memory and learning.
"We've really done a lot to get the concentrations down from where they were in the '70s. But the big message is that some substances that we used long ago are still around, so we must be very careful about the chemicals we put out there today," Hulting concludes.
What To Do
Be wary about eating fish that were caught in the Great Lakes.
If you live near one of the Great Lakes, knowing the recommendations and pollution guidelines in each state is a good idea.
Even if you live elsewhere, it's still important to know the risks surrounding consumption of potentially contaminated fish because not all of them live in the Great Lakes.
Curious about these pollutants? Here's more on DDT, PCBs and dieldrin.
