Written by Quentin Septer

Refrigerators of the early twentieth century were crude contraptions. Using reactive compounds like ammonia, sulfur dioxide, and methyl chloride as coolants, these early fridges weren’t just crude, in fact, they were outright hazardous. On several occasions throughout the 1920s, methyl chloride leaks from household refrigerators ended fatally for hapless residents, and the pressure was on manufacturers to produce safe alternatives. So, when a team of chemists headed by Thomas Midgley, Jr. synthesized a compound called dichlorodifluoromethane—known commercially as “Freon”—back in 1928, it seemed a triumph of science.

Freon belongs to a class of chemical compounds known as the chlorofluorocarbons (CFCs). The molecules don’t exist in nature; they’re uniquely human creations. Non-flammable, non-toxic and remarkably stable, Freon and fellow CFC molecules were embraced as the perfect new refrigerants. By 1935, more than 8 million new CFC-based refrigerators were sold in the United States alone. The compounds were used in air conditioners and freezers, too, among other consumer products. And as American consumerism entered its heyday in the mid-1900s, demand for these wonderfully convenient appliances began to swell like a gaseous plume. By the 1970s, nearly one million metric tons of Freon and other CFCs were being produced every year, generating nearly half a billion dollars in revenue.

Everything was groovy, man, until 1974, when Professor Sherwood Rowland and Dr. Mario Molina discovered the ozone-damaging effects of CFCs. When leaks developed in worn tubing and old refrigerators were inevitably thrown out and replaced, CFCs went airborne. The compounds rose up into the stratosphere, where many of these molecules still hang around today. And up there in the stratosphere, the chemicals are bombarded by sunlight. Energy from incoming solar rays breaks bonds in the structure of the CFC molecule, ejecting chlorine atoms into thin air. The freed chlorine then goes on to wreak havoc on nearby ozone molecules, converting solar radiation-shielding ozone into mere oxygen gas no different than the kind that you and I breathe. 

Plainly, CFCs deplete the earth’s ozone layer. And as the ozone layer is depleted, more DNA-damaging UV radiation can shine down on humans, wildlife and plant life alike. To make matters worse, CFCs act as greenhouse gases, and worse yet, CFCs and their ruinous environmental effects tend to linger.

“These compounds are chemically inert and may remain in the atmosphere for 40–150 years,” Rowland and Molina wrote of CFCs in their 1974 Nature paper, “and concentrations can be expected to reach 10 to 30 times present levels.”

Into the late 1900s, as more CFCs accumulated in earth’s airspace, the planet’s ozone layer began to wear thin. By the late 1970s, a hole in the ozone layer formed over Antarctica. (Incidentally, this “hole” in the ozone layer isn’t a literal hole, as in a spot where all ozone has disappeared, but a region where earth’s ozone layer has thinned significantly.) And this Antarctic ozone hole, too, began to scale with CFC pollution. In 1985, a British climate scientist by the name of Joe Farman and his colleagues, Johnathan Shanklin and Brian Gardiner, documented the world’s thinning ozone layer in their own landmark Nature paper. Between 1975 and 1984, the team found, Antarctica’s ozone levels had declined nearly 40 percent. Connecting their findings to Rowland and Molina’s research of a decade earlier, a story began to emerge. Astronomical amounts of CFCs polluting the stratosphere were directly linked with Antarctica's—and indeed, the world’s—fleeting ozone levels.

The discovery prompted the establishment of the Montreal Protocol—a treaty between 27 countries agreeing to ban the use of ozone-depleting substances. The Montreal Protocol called for a reduction of CFC production to half of 1986 manufacturing levels by the year 2000. A series of amendments later accelerated the phaseout of CFCs, instituting a complete ban of the compounds by 2010, along with additional goals for the phasing out of other ozone-depleting chemicals in the near-future. Today, the Montreal Protocol has been ratified by 197 countries, and CFC production around the world has ceased almost entirely. Since the Montreal Protocol was ratified, global CFC emissions have declined more than 99 percent. But with CFC production outlawed, new and improved “performance chemicals'' were soon developed to fill the consumerist niche left in their wake. New compounds were synthesized and patented for use in freezers and refrigerators and air conditioners and other appliances.

Now, these substitute compounds are causing problems of their own. 

Much like CFCs, these replacement chemicals—hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), among others with even longer, uglier names—have a knack for going airborne. Once afloat in earth’s upper atmosphere, these replacement compounds react with oxygen to form breakdown products known as short chain perfluoroalkylcarboxylic acids (scPFCAs). Belonging to a class of contaminants called persistent organic pollutants (POPs), known colloquially as “forever chemicals,” scPFCAs are remarkably stable. Their many carbon-fluorine bonds make these so-called forever chemicals devilishly resistant to degradation in the environment. As a result, the pollutants, well… persist. Simply put, scPFCAs don’t break down in the environment, and while the compounds form in the far reaches of the atmosphere, they eventually descend to earth’s surface, contaminating landscapes, waterways, plants, animals and human beings alike. And they can fall in the most unexpected places. 

“Deposition on high‐altitude ice caps is solely atmospheric,” a recent study published in Geophysical Research Letters states of scPFCAs and other long-lasting air pollutants. The study began back in 2015, when Cora Young, Assistant Professor in the Department of Chemistry at York University—along with fellow researchers from Memorial University of Newfoundland, Canada and the University of Alberta—traveled to the Canadian high Arctic. The researchers made their way to the glaciers of Canada’s Nunavut territory, where they extracted ice core samples from the Devon Ice Cap and the Mount Oxford icefield. The glaciers of the Great White North provide researchers with a kind of time capsule, trapping and preserving long-lasting global pollutants like scPFCAs in ice—like a photo book of atmospheric history. And when Young and her team analyzed their sampled ice cores, the researchers carried out the first long-term study ever conducted on scPFCA pollution in the global environment.

Professor Young and colleagues tested their sampled ice cores for three species of scPFCAs: trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), and perfluorobutanoic acid (PFBA). Since 1986, around the time the Montreal Protocol was put in place, the atmospheric concentrations of all three scPFCAs have increased tenfold, the team found. In our efforts to remove one pollutant from the atmosphere—CFCs—we’ve swapped them for another: scPFCAs. And, of course, the accumulation of these pollutants is expected to increase with the ongoing use of CFC-replacement chemicals. 

“The Montreal Protocol will undoubtedly continue to positively impact stratospheric ozone and climate and represents an unparalleled achievement in global environmental stewardship.” Young and her team write. “However, this study emphasizes that even the most successful regulations can result in unintended environmental impacts.” 

What kinds of impacts, exactly? 

“Persistent and mobile scPFCAs can circulate in the water cycle and cause irreversible contamination.” Young and colleagues report. “They accumulate in edible plants and are not removed by current drinking water treatment technologies, allowing for multiple pathways of human exposure.” These pollutants are known to contaminate crops grown for human consumption, too. And once they enter the body, scPFCAs appear to accumulate within human lung and kidney tissue, as evidenced by elevated levels of these chemicals in the organs of cadavers.

Still, little is known about scPFCAs and their effects on human beings. TFA toxicity in plants and freshwater invertebrates has been documented in recent research, but the human health effects of TFA and other scPFCAs remain more obscure. The pollutants were detected in human blood serum for the first time early in the year of 2020, as reported in a study published in Environment International. Researchers collected blood samples from 252 study participants in Tianjin, China, and analyzed the contents for 21 distinct forever chemicals. Compared to fellow scPFCAs, TFA was found at the highest concentrations in the human body. In fact, TFA was one of the most concentrated persistent organic pollutants measured in human blood, outnumbered only by perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—two “legacy” pollutants first produced in the 1940s for applications in everything from pots and pans to carpets and flame retardants.

These compounds, PFOA and PFOS, in addition to the scPFCAs, belong to an even larger class of pollutants known as the perfluorinated alkylated substances (PFAS). And all of these so-called forever chemicals have one thing in common: their strong, sturdy chemical bonds allow them to persist in the environment. Both PFOA and PFOS are known to contaminate the drinking water of millions of Americans, and a growing body of scientific literature suggests they may adversely affect human health. Increased rates of birth defects, various cancers, liver diseases, thyroid disorders and endocrine disruption; all have been correlated with human exposure to PFOA and PFOS.

Yet, the full suite of environmental and human health impacts brought on by fellow forever chemicals—the scPFCAs, in particular—remain relatively unexplored in light of these molecules’ perseverance in the environment and known routes of human exposure.

“For these reasons and more,” Young and colleagues write of scPFCAs and their long-lasting nature, “persistence and mobility should be taken into consideration when replacing one class of performance chemicals with another, since this can often lead to unanticipated environmental effects that persist for the foreseeable future.”

Since the Montreal Protocol, regulations have been placed on nearly a hundred ozone-depleting compounds. To date, however, scPFCA emissions have yet to be regulated. But the persistent qualities of CFC-replacement molecules and their breakdown products mean they’re here to stay for the long run. Until effective cleanup technologies can be developed, or until yet another round of replacement chemicals (that don’t form these long lasting break-down products once released into the atmosphere) can be synthesized and implemented in consumer products, scPFCAs will continue to linger and accumulate in the environment—human crops, drinking water and bloodstreams included. 

What effects these compounds will have on ecosystems, wildlife, and human beings alike, nobody can yet say with certainty.