Biodegradable plastic in the form of polylactic acid, or PLA, showed no signs of degradation even after more than a year submerged in the ocean, signalling a need to standardize testing for biodegradable claims, a new study says.
The new study from UC San Diego’s Scripps Institution of Oceanography, published May 24 in the journal PLOS One, tracked the ability of natural, synthetic, and blended fabrics to biodegrade directly in the ocean.
Natural and wood-based cellulose fabrics degraded within a month during experiments conducted off the Ellen Browning Scripps Memorial Pier. The textile samples were placed in flow-through containers deployed both at the sea surface and at the seafloor approximately 10 metres deep.
The study’s lead author, Sarah-Jeanne Royer, a postdoctoral scholar in the Dimitri Deheyn laboratory at Scripps Oceanography, is concerned that certain plastics are increasingly being used to make clothing, rugs and other textiles. Bio-based “biodegradable” plastics made from renewable natural resources such as cornstarch or sugar cane have been marketed as a potential solution to the plastic problem, she says. PLA is one such polymer, and was a focus for the study given its extensive use as a replacement for oil-based, non-biodegradable, materials.
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“This study shows the need for standardizing tests to see if materials promoted as compostable or biodegradable actually do biodegrade in a natural environment,” Royer said in a statement about the study. “What might biodegrade in an industrial setting does not necessarily biodegrade in the natural environment and can end up as marine and environmental pollutants.”
The study also looked at polyethylene terephthalate, a type of polyester often marketed as a “recycled textile”. It is used in textiles, carpets, geotextiles, packaging materials, and disposable medical textiles such as masks.
After submerging the textiles, the team used electron microscopy to examine the fibres at high resolution, and Raman spectroscopy to gain information about the chemical composition and molecular structure of the fibres.
The samples were moved to the Experimental Aquarium at Scripps Oceanography, where they were exposed to controlled conditions of flowing seawater. While the natural, cellulose-based textiles repeatedly disintegrated in 30-35 days, the oil-based and bio-based materials showed no sign of disintegration even after a total of 428 days, the study found.
The diameter of the plastic fibres remained unchanged, as well as the chemical footprint, wrote Royer.
“This comparative study highlights how crucial our language is around plastics,” said Scripps marine biologist Dimitri Deheyn, senior author of the study. “Indeed, a bioplastic like PLA, commonly assumed to be biodegradable in the environment because it contains the prefix ‘bio,’ is actually nothing like that.”
