Saturday, November 06, 2021

How bad is plastic?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video.]

Plastic is everywhere, and we have all heard it’s bad for the environment because it takes a long time to biodegrade. But is this actually true? If I look at our outside furniture, that seems to biodegrade beautifully. How much should we really worry about all that plastic? Did you know that most bioplastics aren’t biodegradable? And will we end up driving cars made of soybeans? That’s what we will talk about today.

Pens, bags, cups, trays, toys, shoe soles and wrappers for everything – it’s all plastic. Those contact lenses that I’m wearing? Yeah, that’s plastic too.

The first plastic was invented in nine-teen-0-seven by the chemist Leo Baekeland. Today we use dozens of different plastics. They’re synthetic materials, molecules that just didn’t exist before humans began producing them. Plastics usually have names starting with “poly” like polyethylene, polypropylene, or polyvinyl chloride. The poly is sometimes hidden in abbreviations like PVC or PET.

You probably know the prefix “poly” from “polymer”. It means “many” and tells you that the molecules in plastic are long, repetitive chains. These long chains are the reason why plastics can be easily molded. And because plastics can be quickly mass-produced in custom shapes, they’ve become hugely popular. Today, more than twenty thousand plastic bottles are produced – each second. That’s almost two billion a day! Chewing gum by the way also contains plastic.

Those long molecular chains are also the reason why plastic is so durable, because bacteria that evolved to break down organic materials can’t digest plastic. So how long does plastic last? Well, we can do our own research, so let’s ask Google. Actually we don’t even have to do that ourselves, because just a year ago, a group of American scientists searched for public information on plastic lifetime and wrote a report for the NAS about it.

For some cases, like Styrofoam, they found lifetimes varying from one year to one thousand years to forever. For fishing lines, all thirty-seven websites they found said it lasts six-hundred years, probably because they all copied from each other. If those websites list a source at all, it’s usually a website of some governmental or educational institution. The most often named one is NOAA, the National Oceanic and Atmospheric Administration in the United States. When the researchers contacted NOAA they learned that the numbers on their website are estimates and not based on peer-reviewed science.

Fact is, no one has any good idea how long plastics last in the environment. The studies which have been done, often don’t list crucial information such as exposure to sunlight, temperature, or size and shape of the sample, so it’s unclear what those numbers mean in real life. Scientists don’t even have an agreed-upon standard for what “degradation of plastic” is.

If anything, then recent peer-reviewed literature suggests that plastic in the environment may degrade faster than previously recognized, not because of microbes but because of sunlight. For example, a paper published by a group from Massachusetts found that polystyrene, one of the world’s most ubiquitous plastics, may degrade in a couple of centuries when exposed to sunlight, rather than thousands of years as previously thought. That plastic isn’t as durable as once believed is also rapidly becoming a problem for museums who see artworks of the last century crumbling away.

But why do we worry about the longevity of plastic to begin with? Plastics are made from natural gas or oil, which is why burning them is an excellent source of energy, but has the same problem as burning oil and gas – it releases carbon dioxide which has recently become somewhat unpopular. Plastic can in principle be recycled by shredding and re-molding it, but if you mix different types of plastics the quality degrades rapidly, and in practice the different types are hard to separate.

And so, a lot of plastic trash ends up in landfills or in places where it doesn’t belong, makes its way into rivers and, eventually, into the sea. According to a study by the Ellen Macarthur Foundation, there are more than one-hundred fifty million tons plastic trash in the oceans already, and we add about 10 million tons each year. Most of that plastic sinks to the ground, but more than 250000 tons keep floating on the surface.

The result is that a lot of wildlife, birds and fish in particular, gets trapped in plastic trash or swallows it. According to a 2015 estimate from researchers in Australia and the UK, over ninety percent of seabirds now have plastic in their guts. That’s bad. Swallowing plastic cannot only physically block parts of the digestive system, a lot of plastics also contain chemicals to keep them soft and stable. Many of those chemicals are toxic and they’ll leak into the animals.

Okay you may say who cares about seabirds and fish. But the thing is, once you have a substance in the food chain, it’ll spread through the entire ecosystem. As it spreads, the plastic gets broken down into smaller and smaller pieces, eventually down to below micrometer size. Those are the so-called microplastics. From animals, they make their way into supermarkets, and from there back into the canalization and on into other parts of the environment from where they return to us, and so on. Several independent studies have shown that most of us now quite literally shit plastic.

What are the consequences? No one really knows.

We do know that microplastics are fertile ground for pathogenic bacteria, which isn’t exactly what you want to eat. But of course other microparticles, for example those stemming from leaves or rocks, have that problem too, and we probably eat some of those as well. Indeed, in 2019 a group of Chinese researchers studied bacteria on different microparticles, and they found that the amount of bacteria on microplastics was less than that on micoparticles from leaves. That’s because leaves are organic and deteriorate faster, which provides more nutrients for the bacteria. It’s presently unclear whether eating microplastics is a health hazard.

But some of those microplastics are so small they circulate in the air together with other dust and we regularly breathe them in. Studies have found that at least in cell-cultures, those particles are small enough to make it into the lymphatic and circulatory system. But how much this happens in real life and to what extent this may lead to health problems hasn’t been sorted out. Though we know from several occupational studies that workers processing plastic fibers, who probably breathe in microplastics quite regularly, are more likely to have respiratory problems than the general population. The problems include a reduced lung capacity and coughing. The data for lung cancer induced by breathing microplastics is inconclusive.

Basically we’ve introduced an entirely new substance into the environment and are now finding out what consequences this has.

That problem isn’t new. As Jordi Busque has pointed out, planet Earth had this problem before, namely, when all that coal formed which we’re now digging back up. This happened during a period called the carboniferous which lasted from three-hundred sixty to sixty million years ago. It began when natural selection “invented” for the first time wood trunks with bark, which requires a molecule called lignin. But, no bug, bacteria, or fungus around at that time knew how to digest lignin. So, when trees died, their trunks just piled up in the forests and, over millions of years, they were covered by sediments and turned into coal. The carboniferous ended when evolution created fungi that were able to eat and biodegrade lignin.

Now, the carboniferous lasted 300 million years but maybe we can speed up evolution a bit by growing bacteria that can digest plastics. Why not? There’s nothing particularly special about plastics that would make this impossible.

Indeed, there are already bacteria which have learned to digest plastic. In twenty-sixteen a group of Japanese scientists published a paper in Science magazine, in which they reported the discovery of a bacterium that degrades PET, which is the material most plastic bottles are made of. They found it while they were analyzing sediment samples from nearby a plastic recycling facility. They also identified the enzyme that enables the bacteria to digest plastic and called it PETase.

The researchers found that thanks to PETase, the bacterium converts PET into two environmentally benign components. Moreover 75 percent of the resulting products are further transformed into organic matter by other microorganisms. That, plus carbon-dioxide. As I said in my earlier video about carbon capture, plastics are basically carbon storage, so maybe we should actually be glad that they don’t biodegrade?

But in 2018, a British team accidentally modified PETase making it twenty percent faster at degrading PET, and by 2020 scientists from the University of Portsmouth had found a way to speed up the PET digestion by a factor of six. Just this year, researchers from Germany, France and Ireland used another enzyme which found in a compost pile to degrade PET.

And the French startup Carbios has developed another bacterium that can almost completely digest old plastic bottles in just a few hours. They are building a demonstration factory that will use the enzymes to takes plastic polymers apart into monomers, which can then be polymerized again to make new bottles. The company says it will open a full-scale factory in twenty-twenty-four with a goal of producing the ingredients for forty thousand tons of recycled plastic each year.

The problem with this idea is that the PET used in bottles is highly crystalline and very resistant to enzyme degradation. So if you want the enzymes to do their work, you first have to melt the plastic and extrude it. That requires a lot of energy. For this reason, bacterial PET digestion doesn’t currently make a lot of sense neither economically nor ecologically. But it demonstrates that it’s a real possibility that plastics will just become biodegradable because bacteria evolve to degrade them, naturally or by design.

What’s with bioplastics? Unfortunately, bioplastics look mostly like hype to me.

Bioplastics are plastics produced from biomass. This isn’t a new idea. For example, celluloid, the material of old films, was made from cellulose, an organic material. And in nineteen 41 Ford built a plastic car made from soybeans. Yes, soybeans. Today we have bags made from potatoes or corn. That certainly sounds very bio, but unfortunately, according to a review by scientists from Georgia Southern University that came out just in April, about half of bioplastics are not biodegradable.

How can it possibly be that potato and corn isn’t biodegradable? Well, the potato or corn is biodegradable. But, to make the bioplastics, one uses the potatoes or the corn to produce bioethanol and from the bioethanol you produce plastic in pretty much the same way you always do. The result is that the so-called bioplastics are chemically pretty much the same as normal plastics.

So about half of bioplastics aren’t biodegradable. And most of the ones that are, biodegrade only in certain conditions. This means they have to be sent to industrial compost facilities that have the right conditions of temperature and pressure. If you just trash them they will end up in landfill or migrate into the sea like any other plastic. A paper by researchers from Michigan State University found no difference in degradation when they compared normal plastics with these supposedly biodegradable ones.

So the word “bioplastic” is very misleading. But there are some biodegradable bioplastics. For example Mexican scientists have produced a plastic out of certain types of cacti. It naturally degrades in a matter of months. Unfortunately, there just aren’t enough of those cacti to replace plastic that way.

More promising are PHAs, that are a family of molecules that evolved for certain biological functions and that can be used to produce plastics that actually do biodegrade. Several companies are working on this, for example Anoxkaldnes, Micromidas, and Mango Materials. Mango Materials. Seriously?

Researchers from the University of Queensland in Australia have estimated that a bottle of PHA in the ocean would degrade in one and a half to three and a half years, and a thin film would need 1 to 2 months. Sounds good! But at present PHA is difficult to produce and therefore 2 to 4 times more expensive than normal plastic. And let’s not forget that the faster a material biodegrades the faster it returns its carbon dioxide into the atmosphere. So what you think is “green” might not be what I think is “green”.

Isn’t there something else we can do with all that plastic trash? Yes, for example make steel. If you remember, steel is made from iron and carbon. The carbon usually comes from coal. But you can instead use old plastic, remember the stuff’s made of oil. In a paper that appeared in Nature Catalysis last year, a group of researchers from the UK explained how that could work. Use microwaves to convert the plastic into hydrogen and carbon. Use the hydrogen to convert iron oxides into iron, and then combine it with the carbon to get steel.

Personally I’d prefer steel from plastic over cars of non-biodegradable so-called bioplastics, but maybe that’s just me. Let me know in the comments what you think, I’m curious. Don’t forget to like this video and subscribe if you haven’t already, that’s the easiest way to support us. See you next week.

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