Researchers led by Lancaster University estimate that CFC replacement chemicals and certain anesthetics caused about a third of a million tonnes (335,500 tonnes) of trifluoroacetic acid (TFA) to be deposited from the atmosphere onto Earth's surface between 2000 and 2022.

The findings suggest the problem is still growing. Because some of these replacement chemicals remain in the atmosphere for decades, TFA pollution is expected to continue increasing. Scientists estimate that annual TFA production from these sources could peak at some point between 2025 and 2100.

What Is TFA and Where Does It Come From?

The study, published in Geophysical Research Letters, used advanced "chemical transport" modeling to track how chemicals move through the atmosphere, react with other substances, and eventually settle back to Earth.

Using this approach, the researchers calculated how much TFA is produced when hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and chemicals used in inhalation anesthetics break down in the atmosphere.

HCFCs and HFCs have been widely used in refrigeration and air conditioning systems. Although these compounds, known as F-gases, are gradually being phased out (following the Montreal Protocol and the later Kigali Amendment), their atmospheric concentrations continue to rise.

TFA is part of a larger family of synthetic chemicals called per- and polyfluorinated alkyl substances (PFAS). PFAS are commonly known as forever chemicals because they resist breakdown and can remain in the environment for extremely long periods.

Concerns About Environmental and Human Health

Scientists are still working to fully understand the long-term effects of TFA. The European Chemicals Agency classifies the chemical as harmful to aquatic life.

Researchers have also detected TFA in human blood and urine. In addition, the German Federal Office for Chemicals recently proposed classifying TFA as potentially toxic to human reproduction.

Some agencies maintain that current environmental levels are below thresholds expected to harm people. However, concerns remain because TFA continues to accumulate and may be extremely difficult to remove once it enters the environment. That growing buildup has prompted calls for TFA to be considered a potential planetary boundary threat.

"Our study shows that CFC replacements are likely to be the dominant atmospheric source of TFA," said Lucy Hart, PhD researcher at Lancaster University and lead author of the study. "This really highlights the broader risks that need to be considered by regulation when substituting harmful chemicals such as ozone-depleting CFCs."

Tracking TFA Across the Globe

To test their calculations, the team compared modeled estimates of TFA production (from chemical breakdown) and deposition with real-world observations, including rainwater measurements and Arctic ice-cores.

The model incorporated data from a worldwide monitoring network that tracks atmospheric concentrations of the source gases and their geographic distribution. As these gases react with other atmospheric compounds, they eventually break down and form TFA.

The researchers also included realistic weather patterns in their simulations. TFA can return to Earth's surface through rainfall or settle directly from the atmosphere onto land and water.

Arctic Ice Reveals the Scale of the Problem

One of the study's most striking findings involved the Arctic. The modeling indicates that almost all of the TFA detected there originates from CFC replacement chemicals, despite the region being far removed from major sources of emissions.

The result highlights just how effectively these chemicals can travel around the world.

"CFC replacements have long lifetimes and are able to be transported in the atmosphere from their point of emission to remote regions such as the Arctic where they can breakdown to form TFA," said Lucy Hart. "Studies have found increasing TFA levels in remote Arctic ice-cores and our results provide the first conclusive evidence that virtually all of these deposits can be explained by these gases."

New Refrigerants May Increase Future TFA Levels

The researchers also identified a growing source of TFA outside the polar regions. Their analysis points to HFO-1234yf, a refrigerant commonly used in vehicle air conditioning systems, as an increasingly important contributor.

"HFOs are the latest class of synthetic refrigerants marketed as climate friendly alternatives to HFCs," said Professor Ryan Hossaini of Lancaster University and co-author of the study. "A number of HFOs are known to be TFA-forming and the growing use of these chemicals for car air conditioning in Europe and elsewhere adds uncertainty to future levels of TFA in our environment."

"There is a need to address environmental TFA pollution because it is widespread, highly persistent, and levels are increasing," said Professor Hossaini.

Scientists Call for More Monitoring

Researchers say the findings underscore the need for a better understanding of TFA pollution and its potential impacts.

"The rising levels of TFA from F-gases is striking. Although HFC use is gradually being phased down, this TFA source will remain with us for decades. There's an urgent need to understand other TFA sources and to assess TFA's environmental impacts. This requires a concerted international effort, including more extensive TFA monitoring in the UK and elsewhere," he said.

Professor Cris Halsall, Director of the Lancaster Environment Centre and co-author, noted that TFA is now known to come from a much wider range of sources than previously believed.

"We've generally viewed TFA as a breakdown product from the use of a few fluorinated pesticides, but it's clear that TFA (a very persistent chemical in the environment) arises from the use and breakdown of a very wide group of organofluorine chemicals including refrigerants, solvents, pharmaceuticals and the PFAS group in general."

Co-author Dr. Stefan Reimann, whose research team in Switzerland closely monitor the atmospheric abundance TFA-forming F-gases, said evidence of increasing contamination is appearing around the world.

"In all regions where TFA measurements are available, a consistent picture of increasing atmospheric concentrations and deposition to Earth's surface is emerging.

"This study is outstanding, as it combines for the first time all the important sources of atmospheric TFA and has a global focus. With increasing use of HFOs, accumulation of TFA in water bodies will potentially grow and this makes long-term monitoring a necessity.