Chemicals brought in to help protect our ozone layer have had the unintended consequences of spreading vast quantities of a potentially toxic 'forever chemical' around the globe, a new study shows.
Atmospheric scientists, led by researchers at Lancaster University, have for the first time calculated that CFC replacement chemicals and anaesthetics are behind around a third of a million tonnes (335,500 tonnes) of a persistent forever chemical called trifluoroacetic acid (TFA) being deposited from the atmosphere across the Earth's surface between the years 2000 and 2022.
And the rate of TFA entering the environment from these sources is continuing to grow as some of these CFC replacements survive for decades in our atmosphere, with peak annual TFA production from these sources estimated to be anywhere from between 2025 and 2100.
Scientists behind the new study, published in the journal Geophysical Research Letters, used 'chemical transport' modelling, which simulates how chemicals move about and change in the atmosphere.
Their model quantified TFA pollution created by the breakdown in the atmosphere of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), which are used in refrigeration, as well as chemicals used as inhalation anaesthetics.
Although these chemicals (known as F-gases) are being phased out (following the Montreal Protocol and the later Kigali Amendment) their presence is still increasing in the atmosphere.
TFA belongs to a class of man-made chemicals called per- and polyfluorinated alkyl substances (PFAS). This group of chemicals are often known as forever chemicals because they do not break down easily and remain in the environment for a long time.
The scientific understanding of TFA is still evolving. The European Chemicals Agency classifies TFA as harmful to aquatic life. TFA has been detected in human blood and urine and the German Federal Office for Chemicals recently proposed that TFA be classified as potentially toxic to human reproduction.
Although some agencies consider that current environmental TFA is below levels that would cause harm to humans, the potentially irreversible accumulation of TFA in the environment has led for calls for it to be designated as a 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."
The researchers compared modelled atmospheric TFA production (from chemical breakdown) and its deposition on the Earth's surface with observation data such as Arctic ice-cores and rainwater measurements.
The researchers provided their model with information on how much of the source gases are present in the atmosphere and where they are located using measurements from a global monitoring network. The source gases react with other atmospheric components and break down to produce TFA.
The model contains realistic weather processes calculating how it is transported and deposited. TFA can be washed out of clouds through rain or deposited directly from the air to the surface.
The modelling shows that almost all of the TFA found in the Arctic, which is far away from known emission sources, is from CFC replacement chemicals and highlights the widespread nature of TFA pollution.
"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."
Away from the poles, at midlatitude regions of the globe, the researchers' modelling also supports evidence around the emergence of HFO-1234yf, which is used in car air conditioning systems, as an important, and likely growing, source of TFA from the atmosphere.
"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.
"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, said: "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: "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."
The study involved researchers from: Lancaster University; the University of Leeds; the University of Urbino; the Commonwealth Scientific and Industrial Research Organisation, Australia; the Norwegian Institute for Air Research; the University of California San Diego; the University of Bristol; the Kyungpook National University, Korea; the Swiss Federal Laboratories for Materials Science and Technology; and the Goethe University Frankfurt.
Their findings are detailed in the paper 'Growth in production and environmental deposition of trifluoroacetic acid due to long-lived CFC replacements and anaesthetics'.
