Questions on ‘eco’ plastics
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Researchers doubt whether biodegradable bags any better than traditional plastic ones
key requirement for developing new biodegradability standard(s) for lightweight carrier bags,” the study said.
Thomas Neitzert, a professor of engineering at Auckland University of Technology and the president of Engineers for Social Responsibility, said the new research helped “destroy” the thinking a plastic bag with a label “biodegradable” was safe for the environment.
“The current standards are not taking properly into account real-life conditions and are therefore underestimating the break-down times of plastic materials,” Neitzert told the NZ Science Media Centre.
The standards were also not accounting for the damage of breakdown particles on marine life when they are digested, he said.
“A biodegradable plastic bag is potentially dangerous to marine life from the moment it enters the water until it dissolves into micro or nanoparticles over many years.”
Neitzert, who was not one of the study authors, said the co-existence of conventional plastic bags and socalled biodegradable plastic bags of compostable materials was also upsetting recycling operations and is confusing the general public.
“Biodegradable plastic bags are in many cases made from crude oil, requiring carbon-based production processes and are emitting CO or methane when degrading,” he said.
“On the way to a low-carbon economy, we should, therefore, carry a reusable bag made from cloth or jute, like our parents did,” Neitzert said.
As with many standards, there was a gap between laboratory testing and the outside world with its constant changing conditions — in this case concerning seasons, temperatures and concentrations of chemicals.
Plastics existed in wastewaters, fresh water and the marine environment and standards never covered all of them, he said. In fact, the standards were usually underestimating the life of a plastic product by years and sometimes decades.
The tests usually lasted only up to six months — apart from marine conditions where they go out to two years — and test conditions were not precisely described in terms of material sizes and inocula, he explained.
University of Auckland chemical sciences lecturer Dr Ivanhoe Leung said there was no single magic bullet to solve the plastic pollution problem.
“Alternative methods, such as the use of plastic-eating bacteria, should be investigated.”
Professor Kim Pickering, of Waikato University’s School of Engineering, said it would be best to design products with end of life in mind.