A new study of PFAS (per- and polyfluorinated substances) in rainwater in the U.S. state of Michigan found trifluoroacetic acid (TFA), an atmospheric degradation product of some f-gases, to be the largest contributor in two out of three sample locations and one of the largest in the third location.
This study was conducted last October by the Michigan-based Ecology Center, Great Lakes PFAS Action Network, Original United Citizens of Southwest Detroit and Environmental Transformation Movement of Flint. The Ecology Center provided funding and technical assistance for the project and reported on its results on its website on May 14.
The Michigan NGOs pursued the study “to better understand if and how PFAS were accumulating in air around heavily industrial areas in Southeast Michigan,” said the Ecology Center, adding that the project “was a low-cost pilot that will help provide direction for future studies.” PFAS, known as “forever chemicals” because of their durability in nature, encompass more than 14,000 compounds, many used to make consumer products like non-stick pans and waterproof clothing; some have been linked to adverse health effects, including cancer, high cholesterol and reproductive toxicity.
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,” noted the Ecology Center. “We know, however, that PFAS can move through air and then to soil and waterways through rain.”
One of the sources of TFA is the 100% decomposition of HFO-1234yf in the atmosphere into TFA, which comes down in rainwater. “TFA travels long distances and is not removed from drinking water using standard filtration methods,” said the Ecology Center. “[It] is not frequently included in water or soil testing yet does show up in high concentrations in rainwater when researchers look for it.” Other sources of TFA include pesticides, sewage treatment and industrial pollution.
Rainwater samples in the study were collected in three areas in Southeastern Michigan – Ann Arbor, Dearborn and Detroit – and analyzed by the College of Wooster in Wooster, Ohio. In addition to TFA, the researchers identified 19 other PFAS chemicals, including the so-called “legacy” compounds PFOS (perfluorooctanesulfonic acid) and PFOA (perfluorooctanoic acid), both of which contain eight carbon atoms and are linked to adverse health impacts. But TFA was by far the largest contributor in the Dearborn and Ann Arbor samples and among the largest contributors in the Detroit sample.
In the test results provided by the Ecology Center, there was 0.15mcg/L of TFA in Ann Arbor rainwater, which represented 88.6% of the total PFAS; 0.22mcg/L of TFA in Dearborn, which accounted for 73.4% of the total; and 0.008mcg/L of TFA in Detroit, which comprised 14%.
The Ecology Center acknowledged that rainwater in the study 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,” said the NGO. “The large variation in TFA among the samples, for example, could be related to the different rain events.”
Under the definition used by the U.S. Environmental Protection Agency (EPA), TFA does not fall into the PFAS category because it has only two carbon atoms. However, scientific authorities define TFA as an ultrashort-chain PFAS because it has one fully fluorinated carbon atom, which is also a characteristic of longer-chain legacy PFAS; that broader definition is being used by the EU as it considers sweeping PFAS regulations.
Other studies
The Michigan study referenced a 2021 study by researchers at the College of Wooster in which the rainwater concentrations of 15 PFAS were measured at six locations in the Ohio-Indiana region of the U.S. during the summer of 2019 and compared them to samples collected at a site in Wyoming. Total PFAS concentrations ranged from 0.05mcg/L to 0.85mcg/L, with TFA being the dominant compound (about 90%). Another U.S. study published in 2023, focusing on households in Indiana, found TFA in samples of dust, drinking water, human blood serum and, to a lesser degree, urine.
Many other studies, particularly in Europe, have found TFA in the environment, including rainwater. For example, the German Environment Agency (UBA) commissioned a TFA measurement program, from February 2018 to March 2020, which reported mean monthly TFA precipitation concentrations up to 4.87mcg/L. One-year TFA inputs amounted to 190 g/km² in 2018/19 and 276 g/km² in 2019/20, an increase of at least three to four times compared to the period 1995/96 (54 to 69 g/km²). The German study tied the TFA in the rain to emissions of HFO-1234yf from mobile and stationary air conditioning.
The mean TFA level found in rainwater in Germany was more than 20 times that of the amount detected in the Dearborn, Michigan, sample. However, HFO-1234yf has been used in car air-conditioning systems as a replacement for HFC-134a for a much longer period in Europe than in the U.S. The EU’s MAC (mobile air conditioning) Directive banned HFC-134a in new models in 2011 and in all new vehicles in 2017. In the U.S., the EPA prohibited HFC-134a in new light-duty cars and trucks as of model year 2021.
Though TFA’s precise effects on human health are still being examined, animal studies of rats and rabbits have found negative impacts on liver and reproduction, respectively. This year, the German Federal Office for Chemicals (BfC) submitted to the European Chemical Agency (ECHA) a proposal linking TFA and its inorganic salts to reproductive toxicity, based on rabbit studies. Some scientists see a parallel between the health findings for PFOA and the potential health effects of TFA.
Even without an established link to adverse health outcomes, TFA’s persistence and accumulation in the environment has raised concerns among scientists. The Ecology Center also called for precautions to be taken for persistent chemicals. “The findings highlight the failures of the existing laws to protect human health and wildlife from the harmful effects of PFAS contamination,” the NGO said in a statement released on June 14. “It is imperative to shift towards a precautionary approach in regulating new and emerging chemicals, prioritizing regulations on chemicals that accumulate and persist in the environment and lead to widespread, long-lasting, and increasing contamination. Current regulations are driven only by risk analysis, which has allowed dangerous and persistent chemicals to infect our environment, water, air, and products, putting our and our world’s health at risk.”
The U.S. EPA in April announced maximum contaminant levels (MCLs) for six PFAS in drinking water, including PFOA and PFOS. The MCL for both PFOA and PFOS is 0.004mcg/L, which is exceeded by the rainwater levels of PFOS found in Detroit (0.0045mcg/L) and Dearborn (0.0046mcg/L) and PFOA detected in Dearborn (0.006mcg/L). There are no drinking water MCLs in the U.S. for TFA, though in Europe limits have been set in the Netherlands (2.2mcg/L), Denmark (9mcg/L) and Germany (60mcg/L, with an advisory level of 10mcg/L). EU has proposed a Drinking Water Directive limit of 0.5mcg/L for total PFAS (though TFA may not be included) that will take effect in 2026.
Like many environmental advocates, the Ecology Center believes PFAS, including TFA, should be regulated as a group rather than individually. “We’ve long advocated for stronger environmental protections when it comes to the tens of thousands of synthetic chemicals currently used by industry,” said Gillian Miller, Senior Scientist at the Ecology Center, in the June 14 statement. “Until our society commits to regulating harmful substances as chemical classes, rather than one by one, this story of chemical bad guys and disillusioned communities will continue to repeat.”
Famed PFAS attorney Robert Bilott also sees “history repeating itself” in the way the chemical industry is downplaying the PFAS risks of f-gases and TFA.
The American Chemistry Council, which represents chemical manufacturers, including f-gas producers, declined to comment for this article.
The chemical industry addressed the environmental deposition of TFA in an October 2021 study funded by the Global Forum for Advanced Climate Technologies (globalFACT), which represents f-gas producers Chemours, Honeywell, Arkema and Koura (and equipment manufacturer Daikin). The study concluded that “with the current knowledge of the effects of TFA on humans and ecosystems, the projected emissions through 2040 would not be detrimental.” But the study also acknowledged that “the major uncertainty in the knowledge of the TFA concentrations and their spatial distributions is due to uncertainties in the future projected emissions.”
“It is imperative to shift towards a precautionary approach in regulating new and emerging chemicals, prioritizing regulations on chemicals that accumulate and persist in the environment and lead to widespread, long-lasting, and increasing contamination.”
The Ecology Center
