Substances used to replace ozone-depleting chlorofluorocarbons (CFCs) may be just as problematic as their predecessors, a new study shows.
In 1987, Canada implemented the Montreal Protocol, a global agreement to protect Earth's ozone layer by ceasing the use of substances like CFCs. Unfortunately, the CFC-replacement substances used to replace them are proving problematic as well, with accumulating levels of their degradation products recently found in the Canadian Arctic.
"In many ways, the degradation products from these substances may be just as concerning as the original chemical they were meant to replace," said Alison Criscitiello, director of the Canadian Ice Core Lab (CICL), housed in the University of Alberta's Faculty of Science. "We are seeing significant levels of these short-chain acids accumulating in the Devon Ice Cap, and this study links some of them directly to CFC replacement compounds."
An ice core drilled on the summit of Devon Ice Cap in the Canadian high Arctic shows a tenfold increase in short-chain perfluorocarboxylic acid (scPFCA) deposition between 1986 and 2014. scPFCAs form through atmospheric oxidation of several industrial chemicals, some of which are CFC replacement compounds. scPFCAs are highly mobile persistent organic pollutants and belong to the class of so-called "forever chemicals" because they do not break down. A few preliminary studies have shown toxicity of these substances to plants and invertebrates.
"This is the first multi-decadal temporal record of scPFCA deposition in the Arctic," explained Criscitiello. "Our results suggest that the CFC-replacement compounds mandated by the Montreal Protocol are the dominant source of some scPFCAs to remote regions."
Over the past four years, Criscitiello and colleagues drilled four ice cores across the eastern Canadian high Arctic. This interdisciplinary work is thanks to a strong collaboration between Criscitiello and the labs of York University atmospheric chemist Cora Young and Environment and Climate Change Canada research scientist Amila De Silva.
These same Canadian Arctic ice cores also contain significant levels of perfluoroalkyl acids (PFAAs). These results demonstrate that both perfluoroalkyl carboxylic acids (PFCAs) and perfluorooctane sulfonate (PFOS) have continuous and increasing deposition on the Devon Ice Cap despite North American and international regulations and phase-outs. This is the likely result of ongoing manufacture, use, and emissions of these persistent pollutants, as well as their precursors and other new compounds in regions outside of North America.
"These results show the need for a more holistic approach when deciding to ban and replace chemical compounds," explained Criscitiello. "Chemicals degrade, and developing a strong understanding of how they degrade in the environment, and what they degrade to, is vital."
The paper, "Ice core record of persistent short?chain fluorinated alkyl acids: Evidence of the impact from global environmental regulations," is published in Geophysical Research Letters(doi: 10.1029/2020GL087535).