Biodegradable bags may be ‘more toxic’ than conventional plastic ones

Tying a plastic bag filled with food scraps in a waste bin
Tying a plastic bag filled with food scraps in a waste bin

Biodegradable plastic shopping bags may be “more toxic” than conventional plastic bags, a Spanish study has found.

Researchers compared the two types of bags in a toxicology test using fish cells.

When the biodegradable bags were used for compost, they registered a higher toxicity level than their plastic equivalents, the study by the Spanish National Research Council found.

“We were surprised that cells exposed to conventional plastic bags showed no traces of toxicity. However, we did detect it in the biodegradable ones, which decreased the viability of the cells,” said Professor Cinta Porte, lead author of the study.

Researchers studied eight single-use plastic consumer products including four biodegradable shopping bags and four conventional plastic products including water bottles, carrier bags and rubbish bags.

“Our hypothesis is that the toxicity is derived from the chemical additives used for processing the materials, as bioplastics, in general, are more difficult to process than conventional plastics,” their report said.

“Manufacturers add chemical additives to make biodegradable bags that could be especially toxic,” it added.

‘It is crucial to investigate’

The researchers said their findings highlighted the “importance of investigating the effects of degradation mechanisms such as composting on the toxicity of compostable plastics”.

“It is crucial to investigate the composition of newly developed formulations for compostable plastics as they may be more harmful than conventional ones,” their report added.

“The widespread usage of compostable plastics and their incomplete degradation may result in increased release of plastic additives and plastic particles to the environment with the consequent adverse implications for the environment and human health.”

Researchers said this was a preliminary study and it was not possible to say what these effects on human health would be.

‘OK for compost’

In 2021, Spain banned the use of conventional plastic bags except for compostable and biodegradable bags. All supermarkets use bags marked as “compostable”.

Biodegradable bags, which can be found in most supermarkets’ fruit and vegetables sections, often have a label reading “OK for compost” which means that they abide by legislation concerning industrial compost.

The study implies that there is a need to revise the toxicological tests currently required to obtain this type of certification, said Dr. Amparo López-Rubio, the co-author of the study.

“More research is needed to guarantee that sustainable and safe formulations are put into the market,” she said

The report was published in the Journal of Hazardous Materials.

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