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Scientists feed fish biodegradable plastic, and the result is not what you might expect

Scientists feed fish biodegradable plastic, and the result is not what you might expect

Although bioplastic appears to be less harmful than ‘normal’ plastic, it still has a negative impact on fish.

You can read it in the magazine The science of the total environment. “Biodegradable plastics may not be the solution to plastic pollution,” concludes researcher Ashley Hogg.

Hawke bases that conclusion on experiments with fish of that species Forsterygion capito. The fish were divided into two groups. One group was continuously fed biodegradable microplastics for five weeks. These plastics are gin – a plant protein found in corn – and chitosan: a naturally occurring biopolymer made from crab and shrimp exoskeletons. During the same period, the other group was given ‘normal’ microplastics (containing polyethylene, a material often used to make plastic bags and bottles). After the fish followed this ‘plastic diet’ for five weeks, the scientists analyzed the behavior of the fish. They looked specifically at how the fish moved (how fast and how far). The flight behavior of the fish was also investigated: how strongly and quickly they responded to threats, how fast they ran, what their maximum speed was, and in what direction they ran.

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 important life processes,” the researchers explain in their study. “It is used by all aerobic organisms to obtain, use and store energy and its disruption 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 ‘normal’ plastic has a negative effect on the swimming movements, flight behavior and aerobic metabolism of fish. Fish that ate biodegradable plastics fared better; Only their maximum speed during flight was affected. This has decreased significantly after the introduction of biodegradable plastics.

Good news and some bad news
The good news is that biodegradable microplastics are less harmful than their petroleum-derived counterparts. But the bad news, Hogg points out, is that they’re completely harmless. “Although they are less harmful, they still have a negative effect on exposed animals. In this case, for example, the population becomes smaller because the flying behavior of fish is affected.

Heavy metals
Hawke is not surprised that biodegradable microplastics also have negative effects on fish “Because the biopolymer used contained traces of heavy metals, which mostly came from the raw materials it was made from, for example chitosan. Even if the concentrations of heavy metals were within the limits set in New Zealand (the country where the experiments were carried out, Ed.) – when it comes to fish and seafood – they could still affect the fish.

An important conclusion is that biodegradable plastics are less harmful than conventional microplastics, but still harmful to fish. But that certainly doesn’t mean it applies to all biodegradable plastics, Haag stresses. “Many biodegradable or biodegradable and edible plastics have already been developed.” It is certainly possible that there is a completely harmless bioplastic among them. But – and this is precisely what matters – we don’t know. “How to make traditional plastics was actually established decades ago, so there is little variation in the way plastics are produced,” explains researcher Bridie Allen. “But because biodegradable plastics are relatively new, there is a lot of variation in the way they are made and the materials used. And this research shows that the raw materials used in these products are important and their use needs to be better regulated and controlled,” agrees Hawke. We must, because the effects of many biodegradable plastics that are already widely produced are unknown.”

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