A New Type of Plastic May Mean Less Litter in Our Oceans

By Mark Miller

Plastic makes up 80 percent of the litter in the world’s oceans. One of the reasons for this is that it takes so long to degrade — hundreds of years by some estimates. But a new variation on an old type of plastic that allows seawater to break it down in just weeks may hold hope for cleaner oceans.

While much of the plastic we use today is made from fossil fuels, a biodegradable plastic that originated in the 1930s made from corn and potato starch is showing new promise. Called polylactide (PLA), it proved to break down faster than conventional plastic — but only in compost, not in water, soil, or seawater.

PLA is a polymer. A polymer is a molecule formed by linking building blocks called monomers together to form a long chain. As reported in Science News for Students, Timo Rheinberger, a PhD student at the University of Twente in the Netherlands, is using genetic science to weaken the links in PLA’s monomer chain to help it break down faster in seawater.

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the genetic molecules that operate all living things. DNA contains the instructions that RNA uses to help make enzymes, proteins, and other substances in cells. DNA contains the instructions and lasts longer. An RNA molecule breaks down after it has carried out its instructions.

Rheinberger and his colleagues took advantage of this behavior. They used parts of RNA molecules to weaken the links of PLA monomer chains. RNA contains chemical groups called hydroxyls that attract water. When these hydroxyl-containing portions of RNA are introduced into PLA’s monomer chain, seawater attacks them and the chemical reaction speeds up the breakdown of the links in the chain.

With 15 percent of PLA’s monomer links weakened, Rheinberger’s study showed that the links broke down completely in two weeks. With only three percent weakened, it took about two years. The variation suggests that weakening PLA’s monomer links can be used to control how quickly — or slowly — they degrade.

Rheinberger believes that more testing is needed. “You need a lot of material to start those studies,” he said, and his team has made only small amounts of modified PLA.

Someday, this modified PLA could find its way into everyday items like cups and plates. It could also be used in 3-D printers, in sutures, and in other industrial and biomedical applications. Hopefully, should it eventually find its way into our oceans, it will disappear much faster than conventional plastic does now.