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An average person uses a typical plastic bag for a period as short as 12 minutes before throwing it away, without thinking about where it might end up.
Yet once shipped to a landfill site, this standard grocery bag takes hundreds, even thousands of years to break down – far more than a lifetime. Bags are an alarming amount of plastic found in the stomachs of whales or bird nests, and no wonder – in the world, we use between 1,000 and 5,000 billion plastic bags a year.
Biodegradable plastic bags are marketed as more environmentally friendly solutions, able to decompose into harmless materials faster than traditional plastics. One company says that its basket "will degrade and biodegrade in a continuous, irreversible and irreversible process" if it ends up becoming a litter in the environment.
In a study published this week in Environmental Science and Technology, researchers tested supposedly ecological bags made from various organic and plastic materials and from UK stores. After three years buried in the garden soil, immersed in the sea water, exposed to light and ambient air or concealed in a laboratory, none of the bags completely collapsed in all environments.
In fact, the biodegradable bags left under the water in a marina could still contain a full load of groceries.
"What is the role of some of these truly innovative and innovative polymers?" Asked Richard Thompson, a marine biologist at Plymouth University and lead author of the study. A polymer is a repetitive chain of chemicals that make up the structure of a plastic, whether biodegradable or synthetic.
"They are difficult to recycle and degrade very slowly if they become waste in the environment," Thompson said, suggesting that these biodegradable plastics could pose more problems than they solve.
What the researchers did
The researchers collected samples of five types of plastic bags.
The first type was high density polyethylene – the standard plastic that we find in grocery bags. It was used for comparison for four other bags labeled as ecological:
Each type of bag has been placed in four environments. Whole bags and bags cut into strips were buried in the garden ground outside, immersed in salt water in a marina, left in the light of day and outdoors, or locked in a dark container in a temperature controlled laboratory.
Oxygen, temperature and light all alter the structure of plastic polymers, said Julia Kalow, a polymer chemist specializing in polymers at Northwestern University, who did not participate in this study. The same goes for reactions with water and interactions with bacteria or other life forms.
What scientists have found
Even in a harsh marine environment, where algae and animals quickly covered the plastic, three years was not enough to dissolve plastics, with the exception of the compostable herbal option, which disappeared under the Water in three months. Bags derived from plants, however, remained intact but were weakened after being buried under the garden soil for 27 months.
The only treatment that systematically destroyed all the bags was exposure to the open air for more than nine months. In this case, even the standard traditional polyethylene bag is disintegrated into pieces after 18 months.
"I would take too long for these products to be considered an environmental benefit," Thompson said.
An egret searches for food among the garbage collected in the Los Angeles River after the floods. Plastic waste can harm wildlife such as birds, fish, turtles and whales. Photo by Los Angeles County Public Works Department / Bob Riha, Jr.
Even if these bags take less time to degrade than traditional plastic bags, they still have enough time to become waste.
And when some of the plastic bags seemed to collapse, such as bags left in the open, it was not clear if the disintegration was complete.
"Was the plastic that was lost simply become smaller pieces of plastic?" Asked Kalow, "Or did it become molecules that could dissolve in water and be consumed?
Future studies, she said, should deepen the fate of these disintegrated plastic particles to determine if they actually decompose and disappear – or if they become microplastics and harmful chemicals.
Why is it important
Even standard plastic bags can not be recycled from your recycling bin. Most of them end up in landfills or are swept away by water or wind and become waste.
Biodegradable and compostable bags are supposed to solve these problems, but the study indicates that this is not the case so far.
These alternative bags are not supposed to end up as garbage on the street or in a natural environment. Ideally, they should all be treated exactly as manufacturers expect it. Biodegradable bags would be buried or, in some cases, recycled in new plastics, at least in theory.
But "even if we can do something recyclable, it does not mean that a commercial recycling plant would be interested in managing it," Kalow said. Biodegradable plastics generally can not be recycled with other plastics. In fact, they can destroy other lots of recyclable plastics, degrading the product until it becomes unusable.
Eco-conscious people should be hopeful that their compostable bags will end up in industrial composting facilities where the high temperatures and favorable conditions for bacteria and other living things will disintegrate them. (Compostable bags in refrigerated and oxygen-free landfills may be retained rather than destroyed.
Plastic bags are part of the rubbish on beaches around the world. Picture from REUTERS / Ricardo Rojas
These are the real problems, said Thompson. Labels like "biodegradable", "compostable" or even "recyclable" are theoretical – they do not reflect the reality of what happens to the materials we throw or throw in the oceans, and do not help people understand precisely how to get rid of them.
Three years after burial or submersion of researchers' plastic bags, they were almost as useful – and as harmful – as the day they were made.
Some simple solutions could help. Thompson suggested that standardized products made from the same sets of materials could streamline our waste management systems and allow much of our waste to be recycled in a cost-effective manner. Kalow, the polymer chemist, said that there might still be hope for new, improved biodegradable plastics if only we could discover this technology.
In the meantime, it's not painful to remember your reusable bag before going to the store.
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