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It certainly is in the Great Lakes. According to raw data from the US EPA-Canada Great Lakes monitoring program, there has been a growing prevalence of  per- and polyfluoroalkyl substances (PFAS) in rainwater in the Great Lakes basin.

Since last August, scientists have analyzed rainfall at six sites across the Great Lakes region: Cleveland, Ohio; Chicago, Illinois; Sturgeon Point, New York; Point Petre in Ontario, Canada; and Sleeping Bear Dunes and Eagle Harbor in Michigan. The team collected ambient and rainwater samples and tested for 38 different PFAS compounds finding high levels at all the sites—in the range of 100-400 parts per trillion (ppt). These chemicals are transported through the air and are deposited in the environment, where they accumulate. The concern?  It can contaminate surface water and soil, which indirectly impacts humans and wildlife.

Interestingly, rainwater from both the rural and urban sites showed high levels of PFAS contamination. In another study, researchers shared findings from testing the rainwater in Ohio and Indiana at the American Chemical Society conference held in the spring of 2021.¹ They used mass spectrometry to identify 17 kinds of PFAS in rainwater collected in summer 2019 at 7 urban, suburban, and rural sites. Detection levels ranged from 50-850 ng/L and samples contained both short-chain and long-chain PFAS.

So this begs the question: How do PFAS get into the rainwater?

To understand that, we need to go back to the early days of PFAS research when researchers were trying to figure out how PFAS were transported to remote environments such as the Canadian Arctic and islands in the middle of the Pacific Ocean. Studies by Scott Mabury’s group at the University of Toronto showed volatile PFAS impurities exist in commercial products that could escape into the air.² Air sampling experiments confirmed that these PFAS volatiles were indeed in the ambient air.

In collaboration with Tim Wallington and his group at the Ford Motor Company in Michigan, additional studies performed in smog chambers showed that these volatile PFAS could degrade and form the commonly known PFAS such as PFOA and lower-chain length perfluorinated carboxylic acids.  This is why the volatile PFAS impurities are typically referred to as PFAS “precursors.” Finally, the PFAS produced from the atmospheric degradation of volatile PFAS precursors can be captured by the moisture in the upper atmosphere and eventually fall to the ground via rain.^2-3

Unfortunately, the PFAS rainwater story gets more complex.  To understand it, we need to discuss how chlorofluorocarbon (CFC) replacement chemicals form ultra-short-chain PFAS.⁴ It is well known that CFCs were phased out in the 1990s under the Montreal Protocol due to their potential to deplete the stratospheric ozone layer. Replacement chemicals included hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs).    

However,  a study by York University Associate Professor Cora Young and her team showed there were unintended consequences to the Montreal Protocol, specifically with regards to PFAS.  The study focused on ice cores that represent what was in the atmosphere for that year.⁴ They measured levels of three ultra-short-chain PFAS (scPFCAs) in ice cores from the Devon Ice Cap in Nunavut, Canada: trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA) and perfluorobutanoic acid (PFBA).  Atmospheric modeling was used to deduce that the majority of the TFA and PFPrA were formed from the CFC replacement chemicals. In contrast, PFBA was mostly from fluorotelomer degradation.    

Although the ice-core study focused on arctic regions, it is expected that southern regions will be more heavily impacted.  More work needs to be done to better understand the global burden of scPFCAs and their sources.  However, it is evident that the presence of PFAS in rainwater is a complex story that will ultimately be unraveled by analytical and atmospheric chemists.

References

1. Pike, K. A., Edmiston, P. L., Morrison, J. J., & Faust, J. A. (2021). Correlation Analysis of Perfluoroalkyl Substances in Regional U.S. Precipitation Events. Water Research, 190, 116685. https://doi.org/10.1016/j.watres.2020.116685
2. Dinglasan-Panlilio, M. J., & Mabury, S. A. (2006). Significant Residual Fluorinated Alcohols Present in Various Fluorinated Materials. Environmental Science & Technology, 40(5), 1447–1453. https://doi.org/10.1021/es051619
3. Young, C. J., & Mabury, S. A. (2010). Atmospheric Perfluorinated Acid Precursors: Chemistry, Occurrence, and Impacts. Reviews of Environmental Contamination and Toxicology Volume 208, 1–109. https://doi.org/10.1007/978-1-4419-6880-7_1
4. Pickard, H. M., Criscitiello, A. S., Persaud, D., Spencer, C., Muir, D. C., Lehnherr, I., Sharp, M. J., De Silva, A. O., & Young, C. J. (2020). Ice Core Record of Persistent Short‐Chain Fluorinated Alkyl Acids: Evidence of the Impact From Global Environmental Regulations. Geophysical Research Letters, 47(10). https://doi.org/10.1029/2020gl087535

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