Toxic "forever chemicals" are entering the Great Lakes through both precipitation and the air — reaching cities of all sizes along the U.S. and Canadian shores, a new study has found.
Levels of the compounds — per- and polyfluoroalkyl substances (PFAS) — remain uniform in precipitation across the lakes but vary in the air depending on the location, according to the study, published on Thursday in Environmental Science & Technology.
“The levels in precipitation don’t depend on the population," first author Chunjie Xia, a postdoctoral associate at Indiana University Bloomington, said in a statement. "They are similar in Chicago, which is heavily populated, and at Eagle Harbor, Michigan, where there’s maybe 500 people living in a 25-kilometer radius."
"That tells us the levels are ubiquitous," Xia continued. "This is the first time we’ve seen that. We’ve never seen that for other pollutants before."
The Great Lakes collectively hold 20 percent of the world's fresh water and 95 percent of North America's fresh surface water supply — with 10 percent of the U.S. population and 35 percent of Canadians calling the basin their home, the authors noted.
Although PFAS have emerged as a serious threat due to their persistence in the environment, the researchers sought to understand the routes by which these compounds — present in industrial discharge, certain firefighting foams and household products — can enter ecosystems.
While the concentrations of PFAS were the same in precipitation basin-wide, their levels in the air were "really different," Xia noted. The highest were in densely populated urban areas, such as Chicago and Cleveland, while the lowest levels were in remote locations.
"That’s similar to what we have observed for other chemicals such as PCBs and pesticides, where the levels are directly related to local population," he said.
Xia and his colleagues also examined differences in location-dependent lake water samples, finding that Lake Superior — the biggest and deepest of the Great Lakes — showed the lowest levels of PFAS.
Lake Ontario, the last in the Great Lakes chain, had the highest concentrations, as well as the most populated cities and industrial centers along its shores, according to the study.
Although Lake Ontario might have the highest levels of PFAS, it also gets rid of the compounds the quickest — by discharging them directly into the St. Lawrence River and the Atlantic Ocean, the researchers found.
In the northernmost lakes, such as Superior, Michigan and Huron, on the other hand, the compounds tend to stay, the authors noted.
The atmosphere constitutes "a really important pathway for delivering PFAS to the Lakes," senior author Marta Venier, an assistant professor in environmental chemistry at the university, said in a statement.
That said, she stressed that the levels she and her colleagues measured in precipitation "are not a concern for people."
“We need to take a broad approach to control sources that release PFAS into the atmosphere and into bodies of water, such as wastewater treatment plants, stormwater, and any sources, since they eventually all end in the lakes,” Venier said.
“We also need to gather more data to determine which of these sources is the major player,” she added.
