Additives for biodegradation of plastic don't work

Researchers from Michigan State University (MSU) have revealed that several additives that claim to break down polyethylene (PE, found in plastic bags) and polyethylene terephthalate (PET, found in soft drink bottles) simply don’t work in common disposal situations such as landfills or composting.

Writing in the journal Environmental Science and Technology, the study authors stated, “Biodegradation-promoting additives for polymers are increasingly being used around the world with the claim that they effectively render commercial polymers biodegradable.” Co-author Professor Susan Selke said the three-year study was funded by package-user companies who wanted to know if these additives actually work.

Image courtesy of MSU.

The MSU team focused on five additives and three categories of biodegradation: biodegradation with oxygen, such as in composting; biodegradation without oxygen, such as in an anaerobic digester or a landfill; and simply burying plastics. According to co-author Professor Rafael Auras, “There was no difference between the plastics mixed with the additives we tested and the ones without.

“The claim is that, with the additives, the plastics will break down to a level in which microorganisms can use the decomposed material as food,” Professor Auras continued. “That simply did not happen.”

The results build on the work of late archaeologist William Rathje, who revealed that even after years underground, chicken bones still had meat on them, grass was still green and that carrots still maintained their orange colour. Since organic materials take so long to decompose, it thus follows that plastics, even with the aid of additives, would take decades or longer to break down, if at all.

The researchers conclude that “anaerobic and aerobic biodegradation are not recommended as feasible disposal routes” for non-biodegradable plastics containing any of the five tested additives. The solution is to limit the use of plastics in the first place, according to Professor Selke, who said, “The proper management of waste plastics is the proper management of waste plastics.”