A new study of households in the U.S. state of Indiana has found TFA (trifluoroacetic acid) – an atmospheric degradation product of HFO-1234yf and other f-gas refrigerants – in samples of dust, drinking water, human blood serum, and, to a lesser degree, urine.
The study says it is the first to report “a substantial prevalence” of TFA and another similar substance in the U.S. indoor environment and the general population, and possibly the first to correlate the presence of TFA in drinking water with TFA in blood samples.
The study, “Elevated Levels of Ultrashort- and Short-Chain Perfluoroalkyl Acids in US Homes and People,” was published by the American Chemical Society in Environmental Science & Technology. Its author is Stephanie M. Eick, Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, Georgia; co-authors are Amina Salamova, Eick’s colleague at Emory University, and Guomao Zheng, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, China.
The study characterized TFA as being part of PFAS (per- and polyfluoroalkyl substances), a category of compounds known as “forever chemicals” for their durability in the environment. In particular, TFA is described as an ultrashort-chain PFAA (perfluoroalkyl acid), with two carbon atoms (one fully fluorinated). Longer (eight-carbon) PFAA include PFOA and PFOS, two of the most regulated PFAS in the world.
The U.S. Environmental Protection Agency (EPA) has defined PFAS to exclude TFA, though it has indicated more flexibility in its definition of late. In June, a U.S. Senate committee proposed a narrow definition of PFAS that would exclude TFA, but this has not yet been moved to a vote. In any case, the definition of PFAS set by the OECD (Organisation for Economic Co-operation and Development), used by scientists worldwide and followed in some U.S. states and the EU, is based on a single fluorinated carbon atom, and includes TFA and some f-gases.
In this study, 47 PFAAs and their precursors were measured in paired samples (324 in total) of dust, drinking water, blood and urine collected in 2020 from 81 Indiana residents. Ultrashort- (with two or three carbons) and short-chain (with four to seven carbons) PFAAs were found to be the most abundant and constituted on average 69−100% of the total PFAA concentrations.
In particular, TFA and another ultrashort-chain PFAA, perfluoropropanoic acid (PFPrA) were the predominant PFAAs in dust, drinking water, and serum. Moreover, a significant positive correlation was found between TFA in dust or water and that in serum, “suggesting dust ingestion and/or drinking water consumption as important exposure pathways.”
This study concludes that “ultrashort- and short-chain PFAAs are now abundant in the indoor environment and in humans and warrants further research on potential adverse health effects of these exposures.”
The most abundant PFAA
The study found TFA in 84% of the dust samples. It was “by far the most abundant PFAA” with a median concentration of 220 ng/g), contributing 75% to the total PFAA concentration in dust.
These findings were similar to those from a recent study from China (with sampling in 2017) that reported TFA and PFPrA as the predominant PFAAs in indoor dust with concentrations of 116−470 ng/g and 35−152 ng/g, respectively.
In drinking water TFA was also found to be the predominant PFAA (median concentration of 79 ng/l) with a detection frequency of 95% and an 84% contribution to the total PFAA concentration. The levels of TFA in drinking water were consistent with those detected in drinking water from the United States collected in 1994−1995 (41−150 ng/l), but lower than those reported from China in 2012 (median 155 ng/l).
The study cited HCFCs and HFCs, as well as fluorinated pesticides and pharmaceuticals, some plastics (such as polytetrafluoroethylene), and aqueous film-forming foams as precursors of TFA in the environment that “may at least partially explain the abundance of TFA in dust and drinking water found in the current study.” However, the study adds that consumption of drinking water and dust intake contributed only about 20% to the total PFAA levels in blood, “suggesting other exposure pathways for these compounds.”
As with the dust and drinking water samples, TFA was the predominant PFAA in blood serum samples (detection frequency 74%, median of 6.0 ng/ml) and constituted 57% of the PFAA concentration. These findings were consistent with those from a recent study from China (sampling year 2017) that reported TFA and PFPrA in serum at median concentrations of 8.5 and 0.48 ng/mL, respectively.
The study noted that protein binding affinity – TFA was reported to bind to proteinaceous fractions and lipids in biota – “could be a driving force behind the bioaccumulation mechanism of the ultrashort- and short-chain PFAAs in human blood.”
In urine TFA was detected in only 31% of the samples but was found at high concentrations in some of the samples, with its maximum concentration reaching 290 ng/ml.
Notably, TFA was the only PFAA for which the blood serum concentrations significantly correlated with both dust and water levels. “To the best of our knowledge, this is the first report of significant correlations between the concentrations of the ultrashort- and short-chain PFAAs in drinking water and serum samples collected from the general population of the United States,” the study says. “These associations suggest that consumption of drinking water may be a significant exposure pathway for these shorter-chain PFAAs, even in the general population with no known PFAS-contaminated sites nearby.”
The study called the high abundance of ultrashort- and short-chain PFAAs in drinking water from municipal sources “a potential environmental health problem that should be taken into consideration in assessing the risk of exposure to PFAS in the general population.”
In addition, a significant positive relationship between the TFA concentrations in dust and those in serum “indicates that dust intake could also be an important exposure pathway for this compound.” By one estimate, two-thirds of household dust comes from outdoors.
The study acknowledges “several limitations,” including a small sample size and a cohort limited in diversity and geographic coverage, adding, “We were not able to determine the contribution of diet or biotransformation of PFAA precursors or fluorinated pharmaceuticals to the total body burden of ultrashort- and short-chain PFAAs.” Thus, it adds, the reported levels of PFAS “should be interpreted with caution.”
Nonetheless, the study says that its findings “warrant urgent research focused on the ultrashort-chain PFAAs to elucidate their sources, potential human exposure pathways, and the effects of these exposures on human health.”
Heidi Pickard, a fourth-year Ph.D. student in the Department of Engineering Sciences at Harvard University, who spoke in June at ATMOsphere America about TFA in the environment, called the TFA study’s findings “pretty significant,” adding that it will be more useful “once additional studies replicate these findings to confirm these levels of TFA are found in other human serum, to make sure that it’s not an artifact of contamination or analytical limitations.”
But she agrees with the study that its findings increases the need to “assess potential human health impacts from the ultra-short chain PFAS. If they’re being detected in serum at these levels, then they must have some affinity for binding to proteins or lipids, which means there’s potential for them to have impacts.”
While TFA’s toxicity for humans has not been fully established, it is known to be toxic in low concentrations to green algae and has been found harmful to animals such as rats and rabbits. Germany’s Environment Agency (UBA) has set a human health “orientation value” limit of 60 mcg/l for TFA in drinking water and a “precautionary measure” of 10 mcg/l. The concentration levels of TFA in the environment have begun to approach – or exceed – those levels in some studies.
Meanwhile, new studies around the world continue to detect TFA in the environment. For example, Chinese researchers have projected, for the first time, China’s annual and cumulative emissions of HFOs, HFO-1234yf and TFA. European chemical testing agency Eurofins found TFA present in 32 drinking water samples from 31 cities in Sweden and Norway in the range 70-720 ng/l. And in a study of PFAS in marine and terrestrial species in the Norwegian environment, researchers found TFA “a major contributor” to the PFAS burden, and “can be important” in the liver of white-tailed eagle, arctic fox and otter.
The chemical industry has taken the position that TFA is not a threat to the environment or human health. Mike Sweeney, Global Commercial Refrigeration Platform Lead, Honeywell, made that point recently at the FMI (The Food Industry Association) Energy & Store Development Conference, in Baltimore, Maryland, citing United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel reports; the Panel issued an update in 2020, which said that “there is no evidence to date” of adverse effects of TFA in drinking water on human health. But the Panel’s report from 2016 noted that “the formation of TFA from the degradation of HCFCs and HFCs warrants continued attention, in part because of its very long environmental lifetime.”
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.”
A request for comment from Honeywell about the new Emory University TFA study did not receive an immediate response.
If [ultrashort-chain PFAS are] being detected in serum at these levels, then they must have some affinity for binding to proteins or lipids, which means there’s potential for them to have impacts.”Heidi Pickard, Harvard University