University of Notre Dame researchers analyzed 42 years of biological records from the Great Lakes, unveiling how per- and polyfluoroalkyl substances (PFAS) or "forever chemicals" have moved across the region, contaminating a variety of wildlife.
The research, spearheaded by a former undergraduate student at the University, was published in the Journal of Environmental Quality. Principal investigators Gary Lamberti, Nieuwland Professor Emeritus of Aquatic Science in the Department of Biological Sciences, Daniele De Almeida Miranda , assistant research professor, and collaborators synthesized 50 studies, which contained 2,500 biological measurements. These observations document the spatial and temporal variation in PFAS in the biota of the largest group of freshwater lakes in the world.
"We focused on the biota, not the water or the sediment, to determine what chemicals get into the organisms from algae and microbes all the way up to the top predators, like salmon and bald eagles," said Lamberti, who is affiliated with Notre Dame's Environmental Change Initiative.
PFAS compounds do not break down because their carbon-fluorine bonds are some of the strongest bonds in chemistry. They resist heat, water and natural degradation, and therefore build up in soil and water. When an organism like algae absorbs the compound, it may be eaten by aquatic insects and fish, which retain the toxin. The concentration of PFAS increases in each step of the food chain, peaking in top predators — a process called biomagnification.
Though there are thousands of types of toxic PFAS, the study focused on six common ones as they were the most detected across the Great Lakes. One specific compound that was phased out of production between 2000 and 2002, perfluorooctanesulfonic acid (PFOS), declined in the Great Lakes during the study period. And while there was high variation in trends among the lakes, the research showed the lowest contamination levels in Lake Superior, with the highest in Lake Ontario. The pattern aligns with population and manufacturing density, Lamberti said. Additionally, this is a result of Lakes Superior and Michigan being larger and deeper.
Peter Martin '24, a former undergraduate student and the lead author on the paper, started the project with Lamberti's team in 2022 at the beginning of his junior year. Martin, now a doctoral student at Michigan State University, used the project as his senior honors thesis. He worked with Miranda and postdoctoral associate Alison Zachritz , among others, as he completed the research.
"There was so much variation within certain periods of time, and then across the entire 42-year timescale," Martin said. "And the thing that was really jarring was that there wasn't one specific temporal trend (a change over a period of time) for all five of the Great Lakes. Each lake had its own specific temporal pattern."
Additionally, the researchers determined that the biomagnification process is not linear, Miranda said.
"There are some different pathways to get to the top of the food web, which are impacted by which groups of organisms that we have," she said. Organisms that remain in the water will amass PFAS both through consumption of other organisms and also through the PFAS circulating in the water.
"But if you have a bird eating a fish, the bird is going to have a different load of PFAS because they don't exchange with the water," Miranda said.
The good news is that if companies phase out a compound — even if it remains pervasive in the environment — it will eventually be flushed out of the lakes, Lamberti said.
However, that "flushing" period varies widely. The average time a single drop of water spends in a lake ranges from less than three years in Lake Erie to 200 years in Lake Superior.
"Unfortunately, the Great Lakes hold onto their water and contaminants for a very long time, meaning that there's ample time for toxins to be taken up by the biota," Lamberti said.
Although the decline of PFOS is a victory, he noted that more compounds continue to be developed on a regular basis that go untested for toxicity.
Miranda is addressing the gaps in the data that Martin amassed during the project — there are many more studies and data about the top-level consumers than for the primary producers like algae and plants. Because there is less data for those organisms, researchers do not know as much about how the PFAS compounds enter the food chain.
"We are collecting several components of the food web, like biofilm, detritus, algae and aquatic insects to see how PFAS enter and circulate at the base of the food web and move up to top predators," she said.
The study was funded by Illinois-Indiana Sea Grant, the Great Lakes Fishery Trust, the Indiana Water Resources Research Center at Purdue University and the University of Notre Dame Environmental Change Initiative.
"We hope that this paper opens the eyes of scientists, industry and the general public, as well as the government, about this persistent problem," Lamberti said. "Even if you remove a compound from production, like PFOS, it's still there, and will be around for decades."
