Bioplastics are not always the greener choice, experiment from FCH BUT shows

"Bioplastics are not a miracle material that will save the environment," explains Jakub Fojt, a PhD student at the FCH BUT, "We have to learn how to use them correctly so that they do not bring more negatives than positives." A series of laboratory experiments in which researchers have compared the effect of biodegradable microplastics and conventional PET microplastics on soil properties should contribute to this.

The increasing amount of microplastics in the environment is leading to a drive to replace conventional plastics with biodegradable ones. However, their use may not always be beneficial, according to research from the BUT.

"We tested the effects of a particular type of bioplastic - poly-3-hydroxybutyrate (P3HB) - on soil properties. This is a biodegradable plastic that can also be produced from used cooking or coffee oil. By biodegradation, the material should completely decompose under the action of the right bacteria. However, it turns out that under inappropriate conditions, biodegradation is very slow or does not occur at all," explains PhD student Jakub Fojt.

"For complete biodegradation to occur, the bioplastic product must be ground into the smallest possible particles and placed in an aggressive environment - for example, in compost, where temperatures rise to 70 °C. However, whole bioplastic cups dumped in the sea or in the forest will definitely not decompose within a few years because the environment is not aggressive enough. Decomposition, or biofragmentation, is more likely to occur," adds Fojt.

Experiments at the FCH BUT have then shown how soil properties can be affected by contamination with P3HB bioplastic, which has degraded into microparticles. In the first experiment, the scientists investigated the effect on the soil's abiotic properties. It is hypothesised that particles of common microplastics can block pores and cause soil drying. In this case, microplastics had the same effect on soil drying as standard microplastics.

The second experiment revealed an even more significant finding. "It showed that increased concentrations of microbioplasts in soil can lead, again compared to standard microplastics, to increased fungal growth. The biodegradation of plastics can also deplete nutrients - specifically nitrogen, which is scarce in the soil. This has had a very significant impact on yields. The soil containing the most bioplastic had 80% lower yields than the soil without contamination," says Fojt.

The third experiment concerned the effect of microbioplasts on the animals living in the soil. "We observed small variations in the birth rate of earthworms. This suggests that the microbioplast could induce stress in them, but we need further experiments to confirm this," explains the PhD student.

Bioplastics are suitable, he says, as long as they are used in appropriate areas and processed in the right way. "I don't see much added value in making biodegradable cups or cutlery. They cannot be recycled and composters don't like to see them in their unground form. Most of the time they end up in landfill or incineration anyway," Fojt tries to point out.

Cups and cutlery labelled as bioplastics can also confuse users when sorting, who sometimes incorrectly classify them in yellow containers as plastic waste. "It is a new material that is very sensitive to higher temperatures. If it gets hot, it starts to break down into monomers or burn. It can contaminate thousands of properly sorted PET bottles," says Fojt, explaining that bioplastics are now best disposed of in mixed municipal waste.

On the other hand, he sees the potential of bioplastics in replacing conventional microplastics in cosmetics, where they act as an abrasive in toothpastes or peeling products. "The particles of such biodegradable plastics are very small and after use they go directly to the wastewater treatment plant, where the environment is very aggressive. The complete biodegradation should therefore take place without any problems," he explains.

According to Foyt, bioplastics are also beginning to be used in the agricultural industry, where they are used as fertiliser carriers or mulch films. Currently, mulch films are mainly made from conventional plastics and farmers should remove them from the field after harvest. "The problem may arise that if the film is labelled as biodegradable, the farmer could plough it into the soil. Without knowing that this increases the concentration of microbioplastics and without proper care will thus deteriorate the soil properties," he adds.

When dealing with biodegradable plastics, he says, education is the most important thing - otherwise they may do more harm than good, as the findings so far suggest. Jakub Fojt wants to use the results of the experiments for follow-up research in real-life conditions, while also opening up a public debate about the limits of bioplastics and proper handling. "It is definitely not a miracle material that will allow people to continue to behave irresponsibly towards the environment and throw away cups in the forest or dump waste in the oceans."