New research highlights the complex ways “forever chemicals” (PFAS) are infiltrating the Great Lakes, identifying atmospheric deposition – specifically rain and snowfall – as a primary and surprisingly uniform source of contamination.
While traditional sources like industrial runoff and wastewater remain significant, a study led by researchers from Indiana University’s O’Neill School of Public and Environmental Affairs reveals that PFAS levels in precipitation are remarkably consistent across the region. Unlike other pollutants that concentrate near cities, PFAS levels in rain were found to be similar in both densely populated areas like Chicago and remote locations like Lake Superior’s Eagle Harbor.
Key Findings from the Research:
- Atmospheric Entry: PFAS enter the lakes through both air and water. While airborne concentrations (gas and particles) are higher in urban centers like Cleveland and Chicago, the concentrations in rain and snow are ubiquitous across the entire basin.
- The “Sink” vs. “Source” Dynamics: Lake Superior: As the largest and most remote lake, it acts as a primary “sink,” accumulating PFAS largely through precipitation. Because it is at the top of the chain, it has the lowest overall concentrations but is a major entry point for the rest of the system.
- Lake Ontario: Located at the end of the chain and surrounded by heavy industry, it shows the highest PFAS concentrations. However, it is also “eliminating” the chemicals faster than the upper lakes by flushing them out through the St. Lawrence River and into the Atlantic Ocean.
- Bioaccumulation in Fish: Separate studies have confirmed that PFAS are present in every fish sampled in Lake Michigan. While some “legacy” PFAS (like PFOS) have seen declines in fish tissue since being phased out of production, newer “short-chain” replacement chemicals are now being detected, the long-term health effects of which are not yet fully understood.
- Sediment and Foam: Researchers found that PFAS also settle into lake-bottom sediments, which can later release the chemicals back into the water. Additionally, PFAS act as surfactants, concentrating in shoreline foam at levels up to 7,000 times higher than in the surrounding water, prompting health warnings for beachgoers.
Why It Matters
The Great Lakes hold 95% of the fresh surface water in the United States and provide drinking water for more than 30 million people. Because these chemicals do not break down naturally, they cycle through the ecosystem for decades.
The study’s lead author, Dr. Marta Venier, emphasizes that because PFAS travel so easily through the atmosphere, local regulations alone aren’t enough. Protecting the Great Lakes will require a broad, international approach to control emissions from wastewater plants, industrial sites, and consumer products before they ever reach the sky.