"Compostable" Plastic Doesn't Biodegrade In The Sea, According To Study

May 26, 2023

If you’re like me, you probably avoid using any kind of disposable cup or lid. But on occasion—like when you’re socializing and don’t want to “make a fuss,” or you’re dying of thirst—you might reach for one that says “compostable” or “biodegradable.” Unfortunately, a new study reveals that bioplastics that are advertised as eco-friendly actually doesn’t biodegrade in the sea.

colorful textiles folded and stacked.

What is bioplastic?

Bioplastic can be 1) plastic made of organic materials such as potatoes, corn, food waste, or wood, or 2) biodegradable and will break down under certain conditions or 3) both. These have become so popular that Coca-Cola even has a 100% bio-PET bottle called “Plant Bottle.” Because it’s made of ethanol (corn), it can market itself as bioplastic—but chemically, it’s identical to petroleum plastic and take just as long to break down.

Plenty of so-called bioplastics do break down fairly easily. I have experienced this first hand when I was invited to a Friendsgiving and poured hot mulled wine into a bioplastic cup, only to see it dissolve before my very eyes. But as it turns out, even this type—the popular polylactic plastic—won’t biodegrade out in the ocean or underground.

Study of bioplastic in the ocean

According to a new study conducted by the University of California, San Diego researchers, “compostable” bioplastic (same polylactic acid in those cups) and plastic fiber textiles failed to degrade after more than a year in the sea. On the other hand, natural fiber textiles all biodegraded in about a month (30–35 days). These natural textiles were: wood-based cellulose such as Lyocell, Modal, and Viscose; and natural cellulose (organic virgin cotton and non-organic virgin cotton). Interestingly a mixture of natural and plastic fibers also didn’t degrade meaningfully. This belies the green marketing that touts these hybrid textiles as a more eco-friendly solution.

“A bioplastic like PLA, commonly assumed to be biodegradable in the environment… is actually nothing like that,”says lead author Dimitri Deheyn.

Today, an estimated 62% of textiles are made from plastic fibers. Although the damaging effects of fast fashion has become more widely known, it’s actually become worse in the past few years. The once-obscure clothing giant Shein is valued at $66 billion, far surpassing (slightly more “conscious” rivals) Zara and H&M combined. Shein churns out up to 10,000 new products each day. The algorithms crawl social media for microtrends that can be put out on the market in real time. The clothes are intended to be worn once and thrown out before you need to launder or care for it. Because I find this so off-putting, I also can’t believe that Shein is now the most downloaded shopping app. But this means there are far, far more people out there who don’t find this repugnant.

What should you do?

So what does this all mean? Unfortunately, it seems that your instincts were right when they told you not to use that “biodegradable” cup at that bohemian chic açai bowl cafe. Be sure to bring your own water bottles, steel straw, and cutlery wherever you go. As for clothing, look for 100% natural fiber. They don’t leach microplastic during washes. And when your garment ends up being discarded—because after so many secondhand stores, it’s not going to be wearable forever—it actually will disappear.

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Photo: Mel Poole via Unsplash


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