Rainwater collection and testing for PFAS

Detecting PFAS in Air Using Rainwater Collection

Published on May 14, 2024

Why Test for PFAS in Rainwater? 

There is growing evidence that PFAS are accumulating in air and spreading through rainwater. Rainwater can contain airborne chemicals so measuring PFAS that accumulate in rainwater is one way to measure PFAS in the air. 

Community members of the Great Lakes PFAS Action Network, and environmental justice community activists in Detroit, Dearborn and Flint, wanted to better understand if and how PFAS were accumulating in air around heavily industrial areas in Southeast Michigan. Through this network the Ecology Center provided funding and technical assistance to support the project. 

This project was a low-cost pilot that will help provide direction for future studies. Rainwater was collected in Dearborn, Detroit, and Ann Arbor by community partners and analyzed by the College of Wooster. 

The state of Michigan has identified many locations contaminated with PFAS from known sources like manufacturing and firefighting foam, but less is known about PFAS accumulation in water and air not near obvious sources. We know, however, that PFAS can move through air and then to soil and waterways through rain. 

In 2022 Michigan tested air for PFAS in 27 locations across the state using two sampler types: the polyurethane foam sampler was designed to capture both particles and gas-phase compounds from air, while the direct air sampler captures gas-phase compounds. Their results showed a wide range of PFAS compounds in the air at levels comparable to air testing in other areas. The outdoor air levels in the Michigan tests showed much lower PFAS levels than other studies measuring indoor air. 

Researchers from the College of Wooster showed PFAS spreading through rain (“atmospheric deposition”) and traveling through the air in Ohio and Indiana. The PFAS profiles at the different sites suggested distinct local sources had a strong influence on rainwater concentrations, although evidence was also seen of distant sources contributing PFAS to rain.

The College of Wooster’s lab’s testing included a PFAS chemical called trifluoroacetic acid (TFA). TFA is a breakdown product of common refrigerants used in air conditioning. It travels long distances and is not removed from drinking water using standard filtration methods. TFA is not frequently included in water or soil testing, yet does show up in high concentrations in rainwater when researchers look for it. 

TFA in air and water is rising sharply across the world. Germany, Denmark, and Great Britain are considering regulating TFA in drinking water due to concerns about its effects on human reproduction and development. Policy makers are facing increased pressure from industries to exempt TFA and refrigerants from policies that would restrict PFAS in products. To do this, industries are pushing definitions of PFAS that would exclude TFA and other refrigerants from regulation. 


Our protocol for collecting the samples was based on work by the North Carolina Department of Environmental Quality and the State of Michigan EGLE. EGLE provided a sampling guidance document: Investigation of Per- and Polyfluoroalkyl Substances (PFAS) In Michigan Rainwater Quality Assurance Project Plan (QAPP), September 2021. Equipment and instructions were provided to the partners who carried out the rainwater collection. A food-grade plastic (PFAS-free) bucket was placed outside before expected rain; the rainwater was then transferred to a glass jar using a funnel. 

Rainwater was collected in Dearborn on 10/30/23, Detroit on 10/13/23, and Ann Arbor on 10/6/23. 

The lab used EPA method 1633 to measure 43 PFAS compounds, including TFA. 

Five-gallon buckets deployed to collect rainwater in Detroit

Findings and Discussion

Test results are shown in Figure 1 and Table 1. All three rainwater samples--one each from Dearborn, Detroit, and Ann Arbor--contained PFAS. Dearborn and Ann Arbor contained TFA as the highest contributor to total PFAS concentration, while the Detroit sample had much lower TFA, although it still was one of the largest contributors to the total. All three locations also contained several other PFAS chemicals, including the so-called legacy compounds PFOS and PFOA.  This is consistent with earlier rainwater analysis in Ohio and Indiana. 

Previous research finds high levels of TFA don’t always correlate with other PFAS chemicals, in part because TFA is more volatile and may travel long distances. Therefore it is helpful to consider the other PFAS separately from TFA.  When TFA is left out of the PFAS total concentration, as shown in Table 1, southwest Detroit and Dearborn stand out as having more than double the amount of PFAS in rain than Ann Arbor. This result may reflect a greater number of industrial sources of PFAS in Detroit and Dearborn. 

A limitation of this small pilot study is the fact that rainwater was collected on different days. Weather conditions such as wind direction, type of clouds, and type of storms can significantly affect the level of PFAS in the air and in the rain that falls. The large variation in TFA among the samples, for example, could be related to the different rain events.

PFAS levels in rainwater may be compared to the U.S. EPA’s drinking water standards, with the caveat that rainwater is not a direct source of drinking water. The EPA standards include limits for six PFAS chemicals. In this study, the levels of PFOA and PFOS in Dearborn and PFOS in Detroit rainwater would exceed those standards. No other detections would exceed the EPA standards; however, it’s important to note that several unregulated PFAS chemicals appeared in rainwater as well. 

PFAS chemicals in rainwater may also be compared to those in air, since rain brings pollutants from air down to earth. Michigan’s 2022 air results from Dearborn and Detroit showed substantial overlap with our rainwater results in those areas. In particular, an array of perfluorocarboxylic acids (PFBA, PFHxA, PFHpA, PFOA, PFNA), as well as PFOS, PFBS and PFOSA, were detected both in air and rain, despite being collected at different times. Only three compounds (PFPeA, PFDA, and PFHxS) were detected in rain Dearborn or Detroit but not detected in the earlier air sampling.

Fully understanding the different PFAS profiles in the air in different locations will require repeated sampling over time. PFAS can be transported everywhere (even the Arctic) and move long distances. Unfortunately, PFAS have been found all over the world in water and rain. However, each site tested in this pilot study has a different chemical profile, which may reflect the fact that while PFAS does transport long distances, local sources influence the levels and types found in rainwater.

Table of Findings: PFAS in Rainwater
Chart of PFAS in rainwater

Action Needed

The presence of multiple PFAS chemicals in rainwater, some at relatively high concentrations, underscores the longtime failures of our national laws to protect humans and wildlife. 

We must break the cycle of producing chemicals that are not evaluated for their persistence in the environment and eventually are discovered to be toxic. Regulation should not be driven only by risk analysis, which has led to chemicals like PFAS globally polluting our water, air, soil, and food, but using a precautionary approach and restricting chemicals based on persistence. This is critical not just for PFAS but for regulating new and emerging chemicals.


This work is a project of the Ecology Center, Great Lakes PFAS Action Network, Original United Citizens of Southwest Detroit, and Environmental Transformation Movement of Flint.


Pike, et al, Correlation Analysis of Perfluoroalkyl Substances in Regional U.S. Precipitation Events. Water Research v. 190, 2021

Taniyasu, et al, Analysis of trifluoroacetic acid and other short-chain perfluorinated acids (C2–C4) in precipitation. Analytica Chimica Acta v. 619, 2008.

Hosea and Salvidge, Rapidly rising levels of TFA ‘forever chemical’ alarm experts, The Guardian, May 1, 2024. Link