Do we need biodegradable plastics?

You often stumble over generally accepted ideas that are oddly illogical. Here’s an example.

Some years ago I attended a conference here in Hamburg. The subject was biodegradable plastic — materials that some of the speakers were developing. The point was that these new materials could be broken down by bacteria in weeks and months and returned to the environment — unlike normal plastic, which survives for years and decades in landfills and the ocean, and will probably never be returned to our natural surroundings.

All this sounded very optimistic and filled the attendees with hope for the future. There was a lot of cheering, and everybody shared the same feeling: the developers of biodegradable plastics were on the right track to saving the planet. Especially since they reduce the CO₂ content of the atmosphere and mitigate the problem of global warming. Everyone shared this feeling, everyone agreed with everything that was said.

For me that is always a strong incentive to question the claims — not to provoke dissonance, but because I genuinely want to better understand the subject. Well, also to provoke dissonance.

Before I continue I must take a minute to stress that I am not a right-wing climate change denier — quite the contrary. And I loathe plastic pollution. I have spoken very rudely to littering citizens, especially in Spain and in Asia, where tossing plastic packaging and utensils carelessly aside, even in the most beautiful natural spots, seems to be part of national tradition.

This is what a beautiful park somewhere in Asia looks like [click to enlarge]

And this is how, on a picnic, you dispose of your plastic plates and bags.

View from a train window [click or tap to enlarge — if you have good nerves]

Occasionally the plastic waste has to be cleaned up…

So I do my best to combat littering and pollution, wherever I go. It is a global problem—except perhaps in Switzerland and Singapore, where pedestrians will retrieve and return to you a chewing gum wrapper you may have “lost.”

At the conference in Hamburg I was asking about the carbon footprint that using plastics has. That was one of the major reasons the experts were advocating biodegradable plastics. It was mainly about combating the increase of carbon dioxide in the atmosphere, about global warming and saving the planet.

But my simple question to the experts was the same as the one I posed to the rain forest scientists: Where’s the carbon stored? Every plastic I know contains a C in its chemical formula, C1 to C10. And in fact the biodegradable plastics we were talking about contained more rather than less of a carbon contingent. Now if bacteria were breaking down plastics, where were they storing the carbon? What happens when biodegradable plastic is biologically reduced to its components? “It is returned to Nature,” I was told.

Unlike all the other participants I was still not satisfied. What does “returned to nature” mean? Biodegradable plastic waste is put into very large composting vats, and kept at a suitably warm temperature until the infused bacteria can break down the plastic into its component chemicals. I was insistent: “After this, what happens to the carbon?” It took a lot of prodding and arguing to get an answer: it is released by the process into the atmosphere, all of it, as carbon dioxide! Is that not counterproductive, I wanted to know? Is biodegradable plastic designed to dump waste carbon into the atmosphere? Qui bono?

Most plastics, of which we are producing around 300 million tons per year, are made from oil, I was told, and just producing them already generates a great deal of carbon dioxide. I remained insistent: does the CO₂ released during the manufacture of plastics exceed the CO₂ saved by using biodegradable materials? Nobody had a convincing answer. The best they could do was to insist that using cloth bags many times over is better for the environment than using disposable plastic bags (which I myself store and reuse, along with cloth bags, many times).

My line of questioning continued—I was genuinely seeking clarification: conventional plastic, I said, comes mainly from oil drilled out of the ground; some biodegradable plastics are also made from petroleum by-products; the ones the conference in Hamburg were celebrating, bio-based plastics, are made solely from plant materials. The plants, I was told, extract huge amounts of carbon from the atmosphere.

But, I remained adamant: the carbon extracted by plants is recycled, not permanently extracted and stored. It is released back into the atmosphere when the bacterial degradation takes over. If the bio-plastic is produced only using plant material — corn, sugar cane — then the process is, at the very most, carbon-neutral. When it is composted in vats, all the CO₂ the plants extracted is returned to the atmosphere. And if it is dumped into the soil or the oceans, where it can be “returned to nature”, then the oxygen-deprived process would in fact turn the carbon into methane, which warms the atmosphere dozens of times faster than CO₂.

So: my conclusion was that biodegradable plastic did at best (when processed in composting vats) nothing for global warming; and if left to decompose naturally in landfills and the oceans, it did more harm than good.

The answer of the experts to my arguments was basically that I did not know what I was talking about — I admitted I was one of the few non-experts in the room. There was rejection, but no empirical or logical refutation of my speculations. I was alone, and the hostility towards me grew.

In such cases I cannot resist: provocation is the name of the game. I told them that the way I see it we should make sure that plastics are not degradable, that they should store their carbon forever. Dig giant pits and bury the stuff that cannot be recycled to new plastics; shred the non-degradable plastics and make bricks or house insulation or road surfaces out of them. Find the best way to recycle plastic, make it into new, usable bags, bottles, and cups. Just don’t let it escape into the atmosphere. Also: use the recycled plastic to make billions of dustbins, and train people, perhaps by force, to dispose of their plastics there.

I did not make any new friends that day. The general feeling was that I was simple-minded, an amateur who did not understand the science, the importance of stopping climate change. And I will admit: I was uncertain about my arguments — as you must be, when they contradict the generally held view of an illustrious expert community. That feeling — that I was wrong for reasons I failed to comprehend — remained until a few weeks ago.

Then I read an article by Wade Roush in Scientific American, December 2019. It is called Wait, Plastic Can Be Good for the Environment? There Wade writes:

Wade Roush says: “Many of our ideas about plastic and the environment are confused. And that may be getting in the way of the fight against global warming. … The hullabaloo [over single-use plastic bags and straws] has spurred restaurateurs to roll out cups and utensils made from biodegradable materials. The popular myth is that you can safely toss such items onto the forest floor or into the ocean, and microbes will break them down into raw materials that will magically be reborn as daisies or seahorses.”

Biodegradable material, he says, is deliberately designed to dump its carbon into the atmosphere at the end of its life cycle. He goes on to tell readers that if we want to save Earth, we need to stop obsessing over biodegradability and start using plastics that are bio-based. And best of all bio-based plastics that are non-biodegradable, like the polyethylene terephthalate (PET), which Coca-Cola and Pepsi have introduced. That would sequester ten billion tons of carbon over the next 30 years— “which would be a good start” (we need to remove tens to hundreds of gigatons of CO₂ from the atmosphere).

Somehow I feel vindicated.