Moves in many jurisdictions around the world to ban the use of single-use plastic bags are laudable, but if the replacement product is a heavier-grade plastic bag billed as “biodegradable” there is little if any evidence to suggest it’s an environmentally helpful substitution.

Indeed, studies into the end-of-life fate of biodegradable plastic bags are so diverse in their findings, and so varied in their protocols, that they are of little use for informing policy or regulation. That’s the central finding of a review of published research into the subject, conducted by a team led by Jesse Harrison of the University of Edinburgh in Scotland.

Harrison and his team looked at available papers investigating the manufacture and whole-life-cycle of biodegradable plastic bags and found that the available findings were inconsistent and often poorly defined.{%recommended 6321%}

The researchers focussed particularly on research into the degradation, or otherwise, of bags reaching the ocean. Currently, the trillion plastic bags produced around the world each year are recognised as a major contributor to marine plastic pollution, comprising a major portion of the estimated five trillion plastic pieces currently in the ocean, collectively weighing 250,000 tonnes.

Despite the size and urgency of the problem, Harrison and colleagues found that many studies used only laboratory tests to predict how particular plastics would behave in the open ocean. There was no agreement across the board on standards to define biodegradability, nor on consistent testing methods.

There was also a notable absence of work on identifying or defining toxins arising from the breakdown of plastics in the ocean over time.

“We argue that current standards and test methods are insufficient in their ability to realistically predict the biodegradability of filmic carrier bags in these environments, due to several shortcomings in experimental procedures and a paucity of information in the scientific literature,” the scientists write in the journal Royal Society Open Science.

“Moreover, existing biodegradability standards and test methods for aquatic environments do not involve toxicity testing or account for the potentially adverse ecological impacts of carrier bags, plastic additives, polymer degradation products or small (microscopic) plastic particles that can arise via fragmentation.”

Plugging these gaps in research, and doing so as soon as possible, should be a priority, they argue, to avoid the nightmare scenario in which trying to remove one environmental pollutant results in the creation of a worse one.