With the enforcement of the Montreal Protocol on 1 January 1989, 198 States committed themselves to drastically reducing the use of chlorofluorocarbons (CFCs) and other brominated and chlorinated chemicals in coolants or as propellants in order to prevent emissions of these ozone-depleting gases as much as possible. The withdrawal was successful, the ozone layer over Antarctica recovered. However, it has now been found that the replacement compounds decompose into persistent organic pollutants that accumulate in water, soil and ice in the northern hemisphere and probably worldwide, according to a new study in the journal Geophysical Research Letters.
The study was conducted as part of an interdisciplinary collaboration between Criscitiello and the laboratories of atmospheric chemist Cora Young of the University of York and scientist Amila De Silva, a scientist for the environment and climate change in Canada. Over the past four years, the team has picked four ice cores in the eastern Canadian high Arctic.
“In many ways, the degradation products of these substances can be just as worrying as the original chemical they were supposed to replace,” said Alison Criscitiello, director of the Canadian Ice Core Lab (CICL) at the University of Alberta. “We see significant amounts of these short-chain acids accumulating in the ice cap on Devon Island and this study directly links some of them to CFC replacement compounds.”
An ice core drilled at the top of the Devon ice cap in the Canadian High Arctic shows a tenfold increase in the deposition of short-chain perfluorocarboxic acid (PFCA) between 1986 and 2014. These acids are produced by atmospheric oxidation of several industrial chemicals, some of which are CFC substitute compounds. The short-chain PFCAs are highly mobile persistent organic pollutants and belong to the class of so-called “forever chemicals” because they do not degrade. “Carbon fluoride is the strongest bond you can have,” says environmental chemist Amila De Silva of Environment and Climate Change Canada. “Persistence is a big problem for the environment, because it is the dose that makes up the poison.”
Currently, little is known about the health risk of short-chain PFCAs, but the compounds are toxic to some plants and invertebrates and accumulate in plants, including food plants. In addition, the ice caps experience accelerated warming, which eventually releases these pollutants into surface water, which, according to the authors, may exacerbate their long-term effects on the environment and society.
“Our measurements provide the first long-term record of these chemicals, all of which have increased dramatically in recent decades,” said Cora Young, an atmospheric chemist at York University in Toronto, Canada and co-author of the new study. “Our work also showed how these industrial sources contribute to the values in the ice caps.”
The same ice cores also contain significant amounts of perfluoroalkyl acids (PFAAs). These results show that both perfluoroalkyl carboxylic acids (PFCAs) and perfluorooctane sulfonate (PFOS) have continuous and increasing deposits on the Devon ice cap, despite North American and international regulations and withdrawals. This is probably the result of the ongoing production, use and emissions of these persistent pollutants, as well as their precursors and other new compounds in regions outside North America.
Public concern focused on long-chain PFCAs that have proven to be toxic to animals, including humans, with adverse effects on reproduction and a tendency to bioaccumulate and concentrate at higher levels of the food chain. They bind to blood and can remain in the body for years, according to De Silva. Long-chain PFCAs are widely used in habitats due to the widespread use of their precursor molecules in industrial and commercial products.
“There is less information about short-chain PFCAs, as found in the new study. They are harder to prove and analyze because they are so small,” De Silva said.
The new study shows the ubiquity of these persistent pollutants and the need to take different environmental hazards into account simultaneously in international agreements, the authors note.
“These results demonstrate the need for a more holistic approach to the decision to ban and replace chemical compounds,” Criscitiello stresses. “Chemicals are degrading and it is vital that a comprehensive understanding is developed of how they degrade in the environment and what they are degraded into.”
Sources: University of Alberta, American Geophysical Union