U.S. Water News Online
OTTAWA, Ontario -- Toxic chemicals absorbed over decades by the Great Lakes are now being exhaled from the waters years after the source of the pollution was cut, according to a study by an environmental group.
Lake Ontario alone released almost two tons of the now-banned PCBs (polychlorinated biphenyls) into the air from 1992 to 1996, said a study released recently by the Integrated Atmospheric Deposition Network.
The five lakes decreased their combined levels of PCBs by 10 tons during the four-year period, while levels of the banned pesticide Deildren decreased four tons, the study said.
Keith Puckett, a researcher with Canada's environment ministry who led the study, said the ``outgassing'' of the chemicals only involved banned substances -- those no longer present in the atmosphere in significant concentrations.
``Think of the lakes as giant lungs that have been sucking in polluted air for the last 50 years,'' he said. ``Now that atmospheric levels of many of these pollutants have dropped below the equilibrium point, the lakes are starting to exhale.''
Puckett said the news shows that the lakes can cleanse themselves once the source of polluting chemicals has been cut.
``It came as quite a surprise to us,'' he said. ``Traditionally we always thought of the Great Lakes as the ultimate destination for many of these toxic chemicals that we find in the atmosphere. It seems now they no longer behave as a repository, but are indeed releasing them back into the air.''
Despite the release of toxic chemicals in the air through the evaporation, Puckett said there was no threat to public health.
``Most of what you get (in toxic contamination) comes in the food that you eat rather than the air you breathe,'' he said. ``I don't think this is a significant concern.''
Scientists say air pollution remains a significant threat to the Great Lakes, and Puckett called for increased efforts to control pollution from power plants, vehicles, and other sources.
PCBs, industrial compounds used to insulate electrical transformers and capacitors, have been banned in the United States and Canada since the mid-1970s but are still widely used in the Third World.
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