Each year, between 1.2 and 2.4 million tonnes of plastic enters the oceans from rivers which can have a disruptive effect on marine ecosystems.
This has led to intensive research for alternatives that decompose faster in nature. Bio-based polymers based on cane sugar are one such option. The most common bioplastic is poly-L-lactide, which is used in 3D printers, textiles, food packaging, disposable cutlery and other applications.
But bioplastics also have a negative impact on biological life, with researchers finding that the behaviour of small perch exposed to bioplastics in fish food changed over a period of six months.
They reacted far more when they met fellow perch than normal. In addition, there were signs of reduced movement, altered ability to form shoals and altered reaction when approached by danger.
"Toxicological experiments that analyse animal behaviour are very rare. Most commonly, researchers look at physiological changes. We can see that something in PLA plastic causes changes in the fish, but we can't see what," said doctoral student Azora König Kardgar.
Because this research looked at PLA microplastic particles, the researchers also tested feeding the perch with kaolin particles, a white clay used for porcelain and to coat paper.
Fish fed with kaolin showed some minor changes in behaviour. However, a male sex hormone was affected and some other gene expressions in the fish were curbed, such as the response to stress.
"We see that PLA is not harmless to fish, so it should not be sold as an environmentally friendly alternative to ordinary plastic. It should be considered as equivalent to ordinary plastic," Azora added.
Fish were fed for six months with food containing 2 per cent PLA, which is about the concentration of ordinary petrochemical plastic used in previous studies. The quantity of kaolin fed to another group of fish was also 2 per cent. In addition, there was also a control group of perch fed with uncontaminated food.
Another research project from last month found that the labelling of some plastics as 'biodegradable' is misleading as they require heat and industrial composting conditions to break down.
Textile samples made from the material were placed in flow-through containers deployed at the sea surface.
While natural, cellulose-based textiles disintegrated in 30-35 days, the oil-based and bio-based materials showed no sign of disintegration even after a total of 428 days.
The UN Environment Programme recently said that plastic pollution could be reduced by 80 per cent by 2040 if countries and companies make policy and market shifts using existing technologies.
