Additives don't help plastics biodegrade

Several additives that claim to break down polyethylene terephthalate and polyethylene are ineffective in landfill and composting, a new study has found.

Michigan State University conducted a three-year study into five additives and three categories of biodegradation - covering the majority of methods available on the market today. They looked at biodegradation with oxygen, such as in composting; biodegradation without oxygen, such as in an anaerobic digester or landfill; and simply burying plastics.

“There was no difference between the plastics mixed with the additives we tested and the ones without,” said Rafael Auras, co-author and MSU packaging professor. “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. That simply did not happen.”

Palaeontology studies have found that even organic matter like chicken bones and carrots don’t decompose even after years underground, suggesting that even with the aid of additives, plastics would take decades or more to break down.

“The solution is to not make claims that are untrue. The proper management of waste plastics is the proper management of waste plastics,” said Susan Selke, co-author of the study and MSU packaging professor.

“Package-user companies funded this study because they wanted to know if the additives that are being marketed to them work. They wanted scientific proof to evaluate the products and disposal approaches that are available to them to break down plastic.”

The results of the study were published in the journal Environmental Science and Technology.