Great Lakes pollution no longer driven by airborne sources; land, rivers now bigger factors

According to Rainer Lohmann, professor of chemical oceanography at the URI Graduate School of Oceanography, water quality in the Great Lakes has been slowly improving for many years. Historic studies of the lakes has usually pointed to atmospheric deposition as the primary cause of pollution in the lakes -- from industrial emissions, motor vehicle exhausts and related sources. But as air pollution has decreased, he has found a shift in the source of Great Lakes chemical pollutants.

"Some contaminants still come from the atmosphere, but it is now mostly from wastewater plants, contaminated industrial sites and inputs from major rivers," Lohmann said. "It's quite a bad mix, but it's getting better. And hopefully the Great Lakes Restoration Initiative will improve things even more."

His research was reported today at the annual fall meeting of the American Geophysical Union in San Francisco.

Lohmann and a team of volunteers deployed passive samplers -- sheets of polyethelene that absorb pollutants -- in the air and water at more than 30 sites around Lake Erie and Lake Ontario from 2011 to 2014. Following chemical analysis, he determined the quantity and source of a variety of pollutants in the lakes.

Legacy pollutants -- those that have been banned for decades but still are detected at relatively high levels, like pesticides and PCBs -- have declined considerably in the lakes, except near the outflows of the Detroit River and the Niagara River and, to a lesser extent, near Erie and Rochester. The waters around Cleveland, however, have lower concentrations of these legacy pollutants.

"Because these pollutants have been banned for such a long time, they're no longer in the atmosphere in high concentrations and so aren't entering the lakes that way," said Lohmann. "But we still see evidence of them coming from Superfund sites and old industrial sites. And the lakes are now cleansing themselves by releasing these old pollutants back to the atmosphere."

Of increasing concern, according to the URI professor, is a group of what he calls "emerging contaminants" that are increasingly being detected in water bodies around the world. These include personal care products, like synthetic musks, and industrial flame retardants, among others.

"Musks come from products like deodorants and shampoos, so they are primarily detected near where lots of people live, since they don't get broken down in wastewater treatment facilities," Lohmann said. "As the lakes are slowly being cleaned of old organic pollutants, they are replaced by all kinds of compounds of emerging concern."