The Arctic can appear to be a pristine, isolated frozen land. But human pollution has reached even this remote corner of the world—which the World Wildlife Fund has called “the chemical sink of the globe.” Now researchers have discovered that a virtually indestructible type of chemical has been building up in the region since the 1990s. The presence of these “forever chemicals” is undoubtedly growing worldwide, scientists say. And the potential impacts on the health of humans and ecosystems are not yet fully known.
The problem paradoxically started because of an effort to fix another environmental issue: the hole in the ozone layer. Under the 1987 Montreal Protocol, countries agreed to phase out ozone-destroying chemicals called chlorofluorocarbons (CFCs). But industry needed something to replace those substances, which were used in a vast range of products ranging from refrigerators to hair spray. Manufacturers turned to chemicals such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs).
When these replacements rise into the atmosphere, however, they react with other chemicals to form several types of substances known as short-chain perfluoroalkyl carboxylic acids (scPFCAs). These compounds then drop down and deposit on Earth’s surface. Because of this process, scientists have suspected since the early 1990s that scPFCAs would increase in the environment. But until now, researchers did not have enough data to understand what was occurring with them over time. “We knew, in theory, it was going to happen. But we didn’t know to what extent it was happening in the real environment,” says Cora Young, an assistant professor of chemistry at York University in Toronto.
To see whether scPFCAs had started accumulating after the Montreal Protocol, Young and her colleagues sampled ice cores from two locations in the Canadian Arctic. Such samples can act as time capsules, recording the chemicals that fall out of the atmosphere and become encased in the ice layers that build up year by year. The depth of the cores meant they covered several decades: one contained 38 years of ice, and the other had 50 years.
Through their analysis, Young and her colleagues found that the amount of scPFCAs in the Arctic has grown significantly, starting in 1990—right around the time the Montreal Protocol took effect. For example, she says that for one of the scPFCAs they looked at, the amount deposited in the Arctic every year is now 10 times greater than it was prior to the treaty. Through computer modeling and comparing trends in chemical production, the team also concluded that the replacement chemicals for CFCs were either the exclusive cause of this increase or one of its major sources. (The researchers found that the fluoropolymer industry, which produces chemicals for products such as nonstick pans, was another source of scPFCAs.) Their results were published in April in Geophysical Research Letters.
Young notes that even though the study only examined Arctic ice cores, scPFCAs are inevitably present in environments all over the planet. That situation is because their precursors—the replacement chemicals—are in the atmosphere worldwide, as are the chemicals that react with them. “If we’re seeing [scPFCAs’] accumulation in the Arctic, that means they’re accumulating everywhere,” Young says. This buildup is potentially problematic, because scPFCAs are extremely persistent chemicals. “They are characterized by carbon-fluorine bonds, which are the strongest single bonds that can be formed,” she explains. “The bonds are so strong that there aren’t really any environmental processes that can break them down.” Any scPFCAs that accumulate in the environment will be there for thousands of years, Young says.
There is some disagreement over the potential toxicity of the scPFCAs looked at in the study. Some experts say they are not a hazard for organisms until they reach much greater amounts than currently exist in the environment. “From what we know now, they’re not toxic at the levels observed or bioaccumulative [capable of building up] in wildlife or humans,” says Ian Cousins, a professor of environmental organic chemistry at Stockholm University in Sweden, who was not involved in Young’s paper. “So it’s unlikely that they’re going to cause any toxic effect on humans or other organisms until they accumulate to a much higher level.” He does note, though, that researchers may discover something new about their toxicity in the future. Chemical industry representatives say that at least one of the study’s identified scPFCAs, called trifluoroacetic acid (TFA), is not problematic. “Previous scientific studies have shown that TFA [presents] negligible risk to organisms higher on the food chain, including humans,” wrote the European Fluorocarbons Technical Committee (EFCTC), which represents fluorocarbon manufacturers in Europe, in a statement to Scientific American. “They do not bio-concentrate in aquatic organisms, and do not bio-magnify in the food chain.” The EFCTC did call the study “robust in general.”
Other experts think there has not been enough research to truly understand whether scPFCAs may be toxic—in particular, at low-dose, chronic levels of exposure. “If [these chemicals] are in the environment for a long period of time, humans and organisms will be continually exposed,” says Jamie DeWitt, an associate professor of pharmacology and toxicology at the Brody School of Medicine at East Carolina University, who was not involved in the April study. “The question is: Is the low concentration in the environment, with consistent exposure, sufficient to overwhelm the body and produce toxicity? That is not known.” That lack of information is because these types of studies are very difficult to conduct. John Ferry, an environmental chemist at the University of South Carolina, who was also not involved in Young’s recent research, agrees that the potential impacts of scPFCAs are not fully known yet. “The fact that studies today don’t necessarily show anything—it’s hard to say how important that really is,” he says. “Even if an effect may be unknown today, [that] doesn’t mean it will be unknown tomorrow.”
Ultimately most experts seem to agree that scPFCAs’ extreme persistence is concerning. “I don’t think it’s a good idea to release these kinds of substances where they never degrade,” Cousins says. “You can be sure that if you continue releasing them, there will be an effect sooner or later that’s going to be problematic. And then you have to wait a long time for that effect to stop, because you can’t reverse the contamination.”
scientificAmerica.com, 12 June 2020