The Great Lakes hold about 21% of the world's surface fresh water and supply drinking water to roughly 30 million people across the US and Canada. For at least four decades, a group of synthetic chemicals has been quietly moving through them.
Study Overview
Researchers at the University of Notre Dame analyzed 42 years of biological records from the Great Lakes, mapping how per- and polyfluoroalkyl substances (PFAS), commonly known as "forever chemicals," have moved across the region and contaminated a wide range of wildlife. The research, published in the Journal of Environmental Quality, synthesized 50 studies containing 2,500 biological measurements, documenting spatial and temporal variation in PFAS across the world's largest group of freshwater lakes.
What PFAS Actually Are
PFAS were invented to be indestructible. The carbon-fluorine bond at their core is one of the strongest in chemistry, resisting heat, water, and biological degradation. This made PFAS useful in nonstick cookware, waterproof clothing, food packaging, firefighting foam, and many industrial applications. It also means they persist in the environment and accumulate. The study focused on six commonly detected PFAS compounds across the Great Lakes, tracking their movement through the food web.
How the Food Web Carries the Load
"We focused on the biota, not the water or sediment, to determine what chemicals get into organisms from algae and microbes all the way up to top predators like salmon and bald eagles," said Gary Lamberti, Nieuwland Professor Emeritus of Aquatic Science at Notre Dame.
When PFAS enter water, algae absorb them. Aquatic insects eat the algae, fish eat the insects, and at each step, PFAS concentration increases—a process called biomagnification. By the time top predators like lake trout or bald eagles are reached, the chemical load is far higher than in the water. PFAS concentrations in natural foams on lake shorelines can be up to 7,000 times higher than in surrounding water, as PFAS are surfactants that build up where air and water meet.
However, the process isn't straightforward. "There are different pathways to the top of the food web, impacted by which groups of organisms we have," said Daniele De Almeida Miranda, assistant research professor and co-investigator. An organism living entirely in water accumulates PFAS through diet and directly from water, but a bird eating a fish gets a different chemical load because it doesn't exchange with water. The route matters and produces different results.
Each Lake Tells a Different Story
Lead author Peter Martin, a former undergraduate who started the project in 2022, noted that each lake had its own temporal pattern. The research showed lowest contamination in Lake Superior and highest in Lake Ontario, aligning with population density and manufacturing activity. Lakes Superior and Michigan are larger and deeper, influencing contamination.
The average time a water drop spends in a lake ranges from less than three years in Lake Erie to 200 years in Lake Superior, meaning contamination introduced decades ago still cycles through the system. "Unfortunately, the Great Lakes hold onto their water and contaminants for a very long time, giving ample time for toxins to be taken up by biota," Lamberti said.
This study shows that contamination of the Great Lakes is not a single event but an ongoing process across a timescale that makes it easy to ignore until numbers become impossible to explain away.
