A new study has found that while natural and wood-based cellulose fabrics degrade within a month, fabrics made of polylactic acid (PLA), a so-called biodegradable plastic, and the oil-based portions of textile blends, show no signs of degradation even after more than a year submerged in the ocean.
The findings: According to the research, bio-based PLA plastic, marketed as an ecologically promising material, and the oil-based polyethylene terephthalate and polypropylene, represent an important source of human-caused pollution, and the fate of how these materials act in a natural environment should be further explored.
- Looking at the structural-chemical degradation of the fibres, significant changes were found in the chemical fingerprint of the cellulose-based materials, while bio- and oil-based plastics remained unchanged.
The study: Funded by the Biomimicry for Emerging Science and Technology (BEST) Initiative from the Deheyn lab with contributions from Lenzing, The Walter Munk Foundation for the Oceans, and Preserve Calavera, the Raman analysis was supported by the Young Thousand Talents Plan of China.
- The study has four co-authors—Sarah-Jeanne Royer as Lead Author from Dimitri Deheyn laboratory at Scripps Oceanography, and currently affiliated with Scripps Oceanography as a visiting scholar from Hawaiʻi Pacific University; Scripps marine biologist Dimitri Deheyn; Francesco Greco, now at the Weizmann Institute of Science, performed the Raman spectroscopy analysis at the Department of Geology of Northwest University, China; and, Michaela Kogler from Lenzing.
The experiment: An experiment conducted off the Ellen Browning Scripps Memorial Pier used ten different types of fabrics, including wood-based cellulose (known commercially as Lyocell, modal, and viscose); natural cellulose (organic virgin cotton and non-organic virgin cotton); bio-based plastic (PLA); oil-based plastic (polyethylene terephthalate and polypropylene), and fabric blends of Lyocell mixed with polyester and polypropylene.
- All these are commonly used in the textiles industry. Polyethylene terephthalate is a type of polyester often marketed as a recycled textile. Polypropylene is used in textiles, carpets, geotextiles, packaging materials, and disposable medical textiles such as masks.
- The textile samples were placed in flow-through containers deployed both at the sea surface and at the seafloor approximately 10 metres (32 feet) deep. Samples were examined every seven days with images taken, and small pieces removed from duplicate samples for further examination in the lab.
- This included scanning 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 then submerged again, in a process that lasted for 231 days at the sea surface and 196 days at the seafloor.
- After conclusion of the Scripps Pier experiment, the samples were moved to the Experimental Aquarium at Scripps Oceanography, where samples 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 natural, cellulose-based materials would disintegrate in about one month, so it would be exchanged for a new sample after the old one disintegrated.
- The natural, cellulose-based samples were replicated five times, while the other materials remained the same for more than a year.
- This study showed that only the natural, cellulose-based fibres in the blends degraded, while the oil-based portion remained intact.
- Additionally, the same type of fabrics were tested in a closed-system bioreactor by an independent company, which replicates a marine environment in an enclosed, indoor system.
- The bioreactor allowed measurements of the percentage of carbon dioxide produced by microbial activity using the fabrics as nutrients, which was thus used as a proxy for measuring biodegradability.
- The cellulose-based materials showed complete biodegradation within 28 days, whereas the oil-based and bio-based fibres did not show any sign of biodegradation.
The backdrop: Startling images of landfills stacked with mountains of thrown away clothing in Chile and Kenya show the global ramifications of fast fashion. An estimated 62%of textiles—68 million tonnes—are now made from plastic fibres and plastic blends, which can persist in the environment for decades to centuries.
- Synthetic textiles also create plastic pollution from microfibres shedding during regular wearing and washing. Most washing machines are not designed to filter for microfibres, that then end up in wastewater, and ultimately the ocean.
What they said:
This study shows the need for standardising tests to see if materials promoted as compostable or biodegradable actually do biodegrade in a natural environment. What might biodegrade in an industrial setting does not necessarily biodegrade in the natural environment and can end up as marine and environmental pollutants. Consumers who are concerned about microfiber plastic pollution should be mindful of the materials they are buying.
— Sarah-Jeanne Royer
Lead Author, Dimitri Deheyn laboratory
This comparative study highlights how crucial our language is around plastics. Indeed, a bioplastic like PLA, commonly assumed to be biodegradable in the environment because it contains the prefix ‘bio,’ is actually nothing like that.
— Dimitri Deheyn