Scientists feed fish with biodegradable plastic and the result is not what you hope

Although bioplastic appears to be less harmful than “regular” plastic, it still has a negative impact on fish.

This can be read in the magazine Holistic ecology. “Biodegradable plastic may not be the solution to plastic pollution,” researcher Ashley Hook concludes.

Hook bases this conclusion on experiments conducted on fish belonging to this species Forestrigion Capito. The fish were divided into two groups. One group was fed regularly with biodegradable microplastic for five weeks. These plastics were made from zein – a plant protein found in corn – and chitosan: a natural biopolymer produced from the exoskeletons of crabs and shrimp. During the same period, the other group was often offered “natural” microplastics (composed of polyethylene, a material also often used to make plastic bags and bottles). After the fish followed this “plastic diet” for five weeks, the scientists examined the fish’s behavior. They looked specifically at how the fish moved (how fast they moved and how far they traveled). The flight behavior of the fish was also examined: how strongly and quickly they responded to threats, how quickly they fled, what was their maximum speed and in what direction they fled.

Oxygen absorption
The researchers also looked at aerobic metabolism by measuring the fish’s oxygen uptake. “Aerobic metabolism is an important physiological mechanism that enables crucial life processes,” the researchers explained in their study. “It is used by all aerobic organisms to obtain, use and store energy, and disrupting it can lead to reduced fitness. Previous research has already shown that exposure to microplastics can affect aerobic metabolism by altering aerobic energy production.”

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Research shows that “regular” plastic has a negative effect on the swimming movements, flight behavior and aerobic metabolism of fish. The fish that ate biodegradable plastic materials fared much better. Only their maximum speed during flight was affected. This turns out to be much lower after exposure to biodegradable plastics.

Good and some bad news
The good news is that biodegradable microplastics are much less harmful than their petroleum-derived counterparts. The bad news, Hook stresses, is that they’re not entirely harmful. “Even though it is less bad, it can still have a negative impact on animals exposed to it. In this case, for example, fish populations could become smaller because the flight behavior of the fish is affected.”

Heavy metals
Houck is not surprised that biodegradable microplastics also have negative effects on fish “Because the biopolymer used contains traces of heavy metals that most likely came from the raw materials from which it was made, for example chitosan. Although the concentrations of heavy metals were within the limits set in New Zealand (the country where the experiments were conducted, ed.) – when it comes to fish and seafood – they still affected the fish.

The fact that biodegradable plastics are less harmful than regular microplastics, but can still have a harmful effect on fish, is an important finding. Hook stresses that this certainly does not mean that this applies to all biodegradable plastics. “Many biodegradable or compostable and edible plastics have already been developed.” It is certainly possible that there is bioplastic among them that is completely harmless. But we don’t know, and that’s precisely what matters. “How conventional plastics are developed has already been established decades ago, so there is not much difference in the way plastics are produced,” explains researcher Bridie Allan. “But because biodegradable plastics are relatively new, there is a lot of variation in the way they are made and the materials used. This research shows that the raw materials used in these materials are important and that their use should be better regulated and monitored. Hook agrees. “More research needs to be done on “The potential effects of biodegradable plastics on marine organisms, because the effects of many widely produced biodegradable plastics are unknown.”

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Megan Vasquez

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