Chemicals introduced to repair and protect the Earth’s ozone layer may have caused unforeseen environmental problems. Some of the substances that have been replaced by ozone-depleting chemicals are now causing large amounts of persistent “permanent chemicals” to be spread around the world, according to new research.
Researchers led by Lancaster University estimate that around a third of 1 million tonnes (335,500 tonnes) of trifluoroacetic acid (TFA) was deposited from the atmosphere to the earth’s surface between 2000 and 2022 due to CFC replacement chemicals and certain anesthetics.
The findings suggest that the problem is still growing. TFA pollution is expected to continue to increase as some of these alternative chemicals persist in the atmosphere for decades. Scientists estimate that annual TFA production from these sources could peak sometime between 2025 and 2100.
What is TFA and where does it come from?
This study Geophysical Research Lettersused advanced “chemical transport” modeling to track how chemicals move through the atmosphere, react with other substances, and ultimately return to Earth.
Using this approach, the researchers calculated the amount of TFA produced when hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and chemicals used in inhaled anesthetics degrade in the atmosphere.
HCFCs and HFCs are widely used in refrigeration and air conditioning systems. Although these compounds, known as F-gases, are being phased out (in accordance with the Montreal Protocol and subsequent Kigali Amendment), concentrations in the atmosphere continue to rise.
TFA is part of a larger family of synthetic chemicals called perfluorinated and polyfluorinated alkyl substances (PFAS). PFAS are commonly known as permanent chemicals because they are difficult to break down and can persist in the environment for very long periods of time.
Concerns for the environment and human health
Scientists are still working to fully understand the long-term effects of TFA. The European Chemical Agency classifies this chemical as harmful to aquatic life.
Researchers have also detected TFA in human blood and urine. Additionally, the German Federal Office for Chemistry recently proposed classifying TFA as potentially toxic to human reproduction.
Some government agencies claim that current environmental levels are below thresholds that are expected to cause harm to people. However, concerns remain because TFA continues to accumulate and can be very difficult to remove once it enters the environment. This growing accumulation has led to calls for TFA to be considered as a potential planetary boundary threat.
“Our study shows that alternative CFCs are likely to be a major source of TFA in the atmosphere,” said Lucy Hart, a postdoctoral researcher at Lancaster University and lead author of the study. “This highlights the wide range of risks that regulations must consider when replacing harmful chemicals such as CFCs, which deplete the ozone layer.”
Track TFA around the world
To test their calculations, the researchers compared modeled estimates of TFA production (through chemical degradation) and deposition to real-world observations such as rainwater measurements and Arctic ice cores.
The model incorporates data from a global monitoring network that tracks atmospheric concentrations of source gases and their geographic distribution. These gases react with other atmospheric compounds and eventually decompose to form TFA.
The researchers also included realistic weather patterns in their simulations. TFA can return to the surface through rainfall or can be deposited directly from the atmosphere onto land or water.
Arctic ice reveals the scale of the problem
One of the study’s most impressive findings concerned the North Pole. The model shows that nearly all of the TFA detected there comes from CFC substitute chemicals, despite the region’s remoteness from major emission sources.
The results highlight how effectively these chemicals can travel around the world.
“Alternative CFCs are long-lived and can be transported through the atmosphere from the point of emission to remote locations such as the North Pole, where they can be broken down to form TFA,” said Lucy Hart. “Studies have found increased TFA levels in remote Arctic ice cores, and our results provide the first definitive evidence that virtually all of these deposits can be explained by these gases.”
New refrigerants may increase future TFA levels
Researchers also identified an increasing number of sources 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 culprit.
“HFOs are the newest class of synthetic refrigerants being marketed as climate-friendly alternatives to HFCs,” said study co-author Professor Ryan Hossaini from Lancaster University. “Many HFOs are known to form TFA, and the increasing use of these chemicals in car air conditioning in Europe and other regions adds uncertainty to future TFA levels in the environment.”
“TFA pollution is widespread, highly persistent, and rising levels, so we need to address it,” Professor Hossaini said.
Scientists call for more monitoring
Researchers say the findings highlight the need for a better understanding of TFA contamination and its potential effects.
“The rise in TFA levels from fluorine gas is alarming. Although the use of HFCs is being phased out, this source of TFA will remain with us for decades. There is an urgent need to understand other TFA sources and assess the impact of TFA on the environment. This requires a concerted international effort, including wider TFA monitoring in the UK and other countries,” he said.
Professor Chris Halsall, director of Lancaster Environment Center and co-author, pointed out that TFA was now known to come from a much wider range of sources than previously thought.
“While we have generally thought of TFA as a degradation product from the use of some fluorinated pesticides, it is clear that TFA, a highly persistent chemical in the environment, results from the use and breakdown of a very wide range of organofluorochemicals, including refrigerants, solvents, pharmaceuticals, and generally the PFAS group.”
Co-author Dr Stefan Reimann said the Swiss research team was closely monitoring the presence of TFA-forming F gases in the atmosphere, and said evidence of increasing pollution was emerging around the world.
“A consistent picture of increasing atmospheric concentrations and surface deposition is emerging in all regions where TFA measurements are available.
“This study is outstanding because it is the first to combine all important TFA sources in the atmosphere and is globally focused. As HFO use increases, TFA accumulation in water bodies could potentially increase, thus requiring long-term monitoring.”
