Even ‘biodegradable’ plastics may not be enough to protect fish from doom, new research suggests

The concept of the spectral figure draped in a white sheet may have lost its terror appeal, but beneath the waves, where polythene bags drift much like shrouded figures, its reign of fear remains uninterrupted.

The extended degradation time of plastics poses one challenge, yet when currents and other natural forces reduce them into smaller, fish-sized bites, a substantial problem arises for our marine friends who ingest them. This results in compromised liver, gut, and immune systems.

So, if we are unable to diminish our reliance on plastics or prevent their influx into the oceans, what measures can we take to safeguard aquatic life? This conundrum gave birth to the idea of "biodegradable plastics," materials designed to break down more rapidly when discarded in landfills or water bodies.

Scientists had long regarded such bioplastics as a panacea for combatting the microplastic-fish issue. However, it turns out that these advanced bioplastics aren't performing as optimally as initially anticipated. While they aren't as detrimental as traditional petroleum-based plastics, exposure to bioplastics still impairs a fish's ability to escape, a critical mechanism for protecting them from predators.

Previous studies have revealed that both traditional and biopolymer microplastic exposure can influence various aspects of a fish's response to danger, such as a decrease in the speed or distance they would travel to elude their assailant. This recent study reaffirmed these findings, observing that fish (specifically a rocky reef species in this instance) tend to exhibit reduced escape velocities when exposed to bioplastics.

Conversely, exposure to petroleum-based polymer microplastics predictably had an adverse impact on fish across the board. Traditional microplastic exposure hindered their responsiveness to danger and their ability to swim away quickly — qualities vital for survival. This also rendered the fish relatively lethargic, affecting their everyday behaviours like mean swimming speed and overall distance covered.

While biopolymers did partially mitigate the harm to fish compared to traditional plastics, the authors expressed concern that impaired escape behaviour would increase the likelihood of predation by birds and other fish. The paper consequently advocates for stricter waste management practices to improve plastic waste control.

"With the escalation in the production of petroleum-derived and bioplastics, it is inevitable that marine organisms will encounter larger quantities of diverse microplastics, thus heightening the risk of microplastic ingestion," the paper observes. "It is important to acknowledge that, although bioplastics may be less environmentally damaging than petroleum-derived polymers, they are not without risks."

The results of this study have been published in the journal Science of the Total Environment and can be accessed here.