How long do discarded straws last?

Straw on the beach

Plastic straws are a major problem for the world’s oceans. © Bryan James/Woods Hole Oceanographic Institution

In order to counteract plastic pollution in the world's oceans, manufacturers are increasingly developing biodegradable straws to replace classic plastic straws. While the latter take years to dissolve in the sea, the environmentally friendly versions do so after just eight to 20 months, as a study has now shown for the first time. The next generation of bioplastics could achieve even better results.

Drinking straws account for around five percent of all coastal and shoreline pollution. If they end up in the ocean, they pose a danger to numerous sea creatures. In order to minimize these harmful consequences of discarded straws, manufacturers are working on several biodegradable alternatives to the classic plastic straw made of polypropylene (PP). In addition to paper, this also includes various bioplastics that are said to decompose quickly in the environment. But exactly how long the different types of straw take to dissolve was largely unknown until now.

Straws in a water bath

Researchers led by Bryan James from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts have now determined for the first time how long it takes seawater to break down discarded straws. To do this, they first filled a large tank in the laboratory with flowing coastal water and imitated the natural marine environment in terms of temperature, light and other environmental factors.

Eight different types of straw ultimately went into the tank, including a classic one made of polypropylene, one made of paper and three made of the bioplastics cellulose diacetate (CDA), polylactic acid (PLA) and polyhydroxyalkanoates (PHA). At regular intervals, the researchers took the straws out of the basin and weighed them to find out how much of their mass had already broken down. James and his team also analyzed the microbial communities that had formed on the surfaces of the stalks.

Which straw disappears the fastest?

The result: After four months, several biodegradable straws, including those made of paper, CDA and PHA, had already lost 25 to 50 percent of their original weight, as the researchers report. From this, James and his colleagues deduce that paper straws thrown into the sea dissolve completely after just ten months, while the alternative made from polyhydroxyalkanoates takes 15 months and the alternative made from cellulose diacetate takes 20 months. However, the team did not notice any change in the mass of the straws made of classic polypropylene and the bioplastic polylactic acid even after four months. So in the natural marine environment, these stalks probably take several years to finally disintegrate.

This is also reflected in the microbial communities that James and his colleagues found on the respective straws. Microorganisms that metabolize polymers had settled on most of the biodegradable variants. However, only “normal” microbes lived on the straws, which were difficult to degrade. “This result suggests that these materials only provide surfaces for the settlement of microorganisms and not substrates for their metabolism,” explain the researchers. Accordingly, the microbes find an anchorage there, but no food.

But which is the best and most sustainable straw? The paper straw decomposes the fastest, but it is not very user-friendly. Many customers complain that it begins to break down in the drink and at some point no longer offers a pleasant drinking experience. James and his team therefore favor the straw made from cellulose diacetate (CDA), which is made from pulp. More specifically, a previously unreleased prototype made of foamed CDA: “The unique thing about this foam straw is that it has a shorter lifespan than the paper straws, but still retains the properties of a plastic or bioplastic straw,” says James. It would therefore be a good compromise between environmental and user-friendliness.

Source: American Chemical Society, Woods Hole Oceanographic Institution; Technical article: ACS Sustainable Chemistry & Engineering, doi: 10.1021/acssuschemeng.3c07391

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