Persistent pollutants and the unintended side effects of the Montreal Protocol

The 1987 Montreal Protocol, which banned chemicals that destroy the Earth's protective ozone layer, is one of the great environmental success stories. Now, the alternatives to those chemicals are showing up in Arctic ice, and we don't know if they pose a threat to human health.

During the 1980s, scientists noticed that ozone, an altered form of oxygen found in the upper layers of the atmosphere, was disappearing at alarming rates, especially around the South Pole. Ozone is a natural sunscreen, filtering out harmful ultraviolet radiation from the sun. The scientists feared that if the ozone layer disappeared, life on Earth would be threatened with increased cases of skin cancer and other harmful UV effects.

The culprit was chlorofluorocarbons, or CFCs, that were widely used in refrigeration, air conditioners and as propellants in aerosol cans. When these chemicals were released into the atmosphere, they would drive chemical reactions that converted UV-absorbing ozone into ordinary oxygen.

In response, the United Nations gathered world leaders and scientists in Montreal to sign a treaty banning these chemicals worldwide. One hundred ninety-seven member states, representing every country on Earth, signed the treaty and slowly, over the decades since, the ozone layer has begun to recover.

The Montreal Protocol was a celebrated example of science pointing to an environmental problem, then governments and industry responding quickly and effectively to solve it. Many have hoped it could be the blueprint for similar action on climate change.

One of the reasons the ban on CFCs was politically possible was that there were substitute chemicals available. What we've learned since 1987, however, is that these substitute chemicals are not always benign. 

Substitutes have their own issues

Take hydrofluorocarbons, or HFCs, for example. They worked well in refrigeration and did not interact with ozone. Problem solved — or so it seemed. Unfortunately HFCs are potent greenhouse gases, with some varieties having more than a thousand times more heat-trapping potential by weight than carbon dioxide. An amendment to the Montreal Protocol treaty will see their use substantially reduced over the next 30 years.

A number of alternative chemicals are now used for refrigeration. While they don't destroy ozone and are not greenhouse gases, some of these substances are spreading in the environment and can be incredibly durable, so they can be a source of persistent organic pollution, which many environmental scientists are concerned about.

A new Canadian study found traces of perfluoroalkylcarboxylic acids (scPFCAs) in ice cores drilled in the Arctic. These chemicals are produced when some CFC replacements oxidize in the atmosphere. When the researchers compared the amount of these chemicals in the ice to historical records, the scientists found that levels appeared in the 1990s and have been increasing since.

These scPFCAs are part of a family of persistent organic pollutants from many sources, an alphabet soup of chemicals, including perfluoroalkyl acids (PFAAs) and perfluorooctane sulfonate (PFOS). There is increasing concern about these substances as evidence emerges about their potential toxicity.

If chemicals used in technology from the South can make it all the way into Arctic ice, that means they have the ability to spread around the globe. And a big concern among the scientists is that these chemicals are incredibly persistent. They don't easily break down in the environment. 

The authors say in their scientific paper, "Persistent and mobile scPFCAs can circulate in the water cycle and cause irreversible contamination. They accumulate in edible plants and are not removed by current drinking water treatment technologies, allowing for multiple pathways of human exposure."

More work is needed to determine whether there are significant health impacts from these chemicals, but it's clear that they're going to be with us for a very long time. And this suggests that even the best efforts to prevent environmental damage can have unintended side-effects in the long-term.