Researchers with Minnesota Sea Grant say new findings from a two-year study show PFAS contamination is consistently entering the Great Lakes region through rain and snow.

The project, funded by the United States Geological Survey, monitored precipitation at five locations across Minnesota and Michigan and detected PFAS in every sample collected.

The research will be presented in June at the National Atmospheric Deposition Program Scientific Symposium in Madison, Wisconsin.

Scientists involved in the project say the results strengthen evidence that airborne PFAS pollution is widespread and may travel long distances before settling into watersheds, lakes and surrounding ecosystems.

The findings also raise concerns about the limits of current PFAS monitoring methods. Researchers discovered that routine testing captures only a small fraction of fluorinated chemicals present in precipitation, suggesting environmental contamination may be more extensive than previously understood.

PFAS detected in all samples during two-year study

PFAS are synthetic chemicals widely used in consumer and industrial products, including nonstick cookware, waterproof clothing, firefighting foams and food packaging.

Because many PFAS compounds degrade extremely slowly, they are often referred to as forever chemicals.

The new study focused on atmospheric deposition, the process by which airborne chemicals return to Earth through precipitation.

Weekly rain and snow samples were collected over two years to better understand how PFAS enters the Great Lakes environment.

Project lead Alex Frie, research and fellowship coordinator with Minnesota Sea Grant, said researchers were surprised by both the consistency of PFAS detection and the changing chemical makeup of the samples.

According to Frie, continuous PFAS monitoring allowed researchers to identify short-term spikes in contamination levels that might otherwise have been missed through less frequent testing.

The study found that atmospheric deposition appears to be a persistent source of PFAS contamination throughout the region.

Atmospheric modelling traces potential pollution sources

Researchers also used atmospheric transport modelling to examine the paths of air masses before precipitation events.

By comparing weather patterns with PFAS measurements, scientists are beginning to identify possible source regions linked to contamination.

Miguel Bernardez, a postdoctoral associate involved in the study, said tracking atmospheric transport at this scale is highly complex because researchers are analysing trace chemical concentrations spread across large geographic areas.

The modelling work supports growing evidence that PFAS pollution is not confined to wastewater discharge sites or industrial facilities near waterways.

Instead, airborne transport may allow PFAS and related fluorinated chemicals to move hundreds of miles before being deposited through rainfall or snowfall.

That finding has major implications for environmental management across the Great Lakes basin, where regulators and researchers are increasingly focused on regional pollution pathways rather than isolated local sources.

Current PFAS monitoring may miss hundreds of chemicals

A third analysis presented by the research team examined whether existing PFAS monitoring programmes adequately measure the full range of fluorinated chemicals in the environment.

Graduate researcher Quinn Whiting compared measurements from 33 commonly monitored PFAS compounds against broader testing for extractable organic fluorine.

The results showed that standard PFAS tests accounted for only a small share of total fluorinated chemicals detected in precipitation samples.

Additional screening identified roughly 300 distinct fluorinated chemical signals, including pesticides, pharmaceutical compounds, PFAS precursors and other substances not routinely included in environmental testing programmes.

Whiting said many people assume that standard PFAS monitoring captures all contamination, but current approaches measure only a limited subset of the thousands of PFAS compounds believed to exist globally.

The findings suggest advanced non-target analysis techniques could become increasingly important for understanding the true scale of PFAS contamination in the Great Lakes region.

Long-term PFAS monitoring could shape future policy

Researchers also observed seasonal shifts in atmospheric contamination levels, with some fluorinated compounds increasing during spring and summer before declining in winter months.

Scientists involved in the project say the work could help environmental agencies develop more accurate PFAS budgets for watersheds and improve pollution management strategies across the region.

The study adds to a growing body of evidence that atmospheric transport plays a significant role in spreading PFAS contamination throughout the Great Lakes ecosystem.