Biodegradable plastics may end up doing more harm than good
FOR those guilt-ridden about the environmental damage caused by everyday consumer purchases, there are myriad paths toward forgiveness. Stick your bottles, cans, and Amazon cartons into the recycling box. Buy the organic cold brew that’s made with 100% renewable power. Minimize the carbon from your ski holiday flight with Peruvian rainforest offsets.
Then there’s biodegradable plastics. It’s hard to cut polymers from your life when boxed blueberries are so temptingly cheap and so healthy — but perhaps we can at least mitigate the effects if we buy them in a box that will turn into compost?
Chemicals companies are paying attention. Production capacity for plant-derived and biodegradable products will triple over the coming five years to 6.3 million metric tons, according to European Bioplastics, an industry association. That sounds like a drop in the ocean next to the roughly 400 million tons a year plastics market, but it could grow rapidly. Project Drawdown, a climate think-tank, envisages between 92 million tons and 357 million tons of bioplastics production by 2050.
If you think the only problem posed by plastics is waste management, we should be welcoming this trend. Biodegradable plastics are meant to break down in the environment in weeks or months, rather than the decades or centuries that conventional ones can hang around. However, with consumption of polymers predicted to double by 2040, another issue ought to come into focus: emissions.
Like gasoline, Vaseline, and asphalt, most of the world’s plastics are byproducts of the oil refining industry, accounting for about 8% of total oil consumption. That proportion is likely to rise drastically in the coming decades as electric vehicles displace combustion engines in road transport, reducing the share of the oil barrel going into fuel. They differ from fossil fuels in a crucial way, however. Using a ton of jet kerosene pumps more than three tons of carbon dioxide into the atmosphere, as burning pulls apart its hydrocarbon molecules. A plastic pipe, on the other hand, is only useful if it remains chemically stable. Its carbon must remain locked tight inside its chemical structure, or it will weaken and shatter.
Biodegradable plastics change that dynamic. In breaking down, they release their carbon back into the environment — particularly as methane, one of the most potent greenhouse gases. As a result, life-cycle emissions may end up being greater than those from conventional alternatives. One 2020 US study of polylactic acid, or PLA, derived from cornstarch and commonly used in disposable food containers, found that its total emissions were greater than those of conventional plastics, except in cases where it remained inert after being trashed.
Not all bioplastics are created equal. The same study found that bio-polyethylene, a plantderived polymer that doesn’t break down, may suck up more carbon than it emits. That calculation demonstrates that biodegradability is just one of a series of good and bad factors relating to different varieties of plastics, rather than a simple and absolute positive.
The greatest risk is that we allow the virtuous glow of compostable polymers to blind us to their potential downsides. While most biodegradable plastics are made from biomass such as starches and crop residues, they can also be made from fossil fuels. That’s a worst-of-all-worlds situation, in which the emissions released in landfill aren’t even offset by carbon sucked out of the atmosphere by the plants used as feedstock. It may also be the segment of the bioplastics market that grows fastest over the coming years. PBAT — a fossil-derived alternative to the polyethylene used in plastic wrapping, bags and bottles — appears to be winning the race in China, with a government-commissioned study forecasting production will hit 7 million metric tons in 2025, compared to 1 million tons for PLA.
One advantage of the mountains of waste created by our voracious appetite for plastics is that it’s a highly visible problem. That means we’re motivated to tackle it. If the dozen developing countries that generate nearly nine-tenths of the world’s marine plastic could lift their waste management to developed-economy levels, the oceans would be drastically cleaner. Improving recycling rates worldwide from current levels of less than 10% to those of more than 40% common for packaging in Europe would help even more.
Emissions from plastic degradation — an invisible process taking place deep underground, and producing no emotive imagery of floating debris, tangled turtles, or overflowing waste dumps — may be far more insidious. Bioplastics “are not permanent solutions because they still reaffirm the take-make-waste linear economy mindset,” said Alice Zhu, a researcher into plastic pollution at the University of Toronto.
To businesses, the green aura given off by bioplastics is an advantage, helping to reconcile busy consumers to the polymers we use every day. In environmental terms, that’s precisely the problem: they risk absolving us of the need to carry out the basic work of reducing, reusing and recycling. Ultimately, that’s the only way that we’ll deal with our plastics addiction. ■
In breaking down, biodegradable plastics release their carbon back into the environment — particularly as methane, one of the most potent greenhouse gases. As a result, life-cycle emissions may end up being greater than those from conventional alternatives.