Scientists warn that green alternatives plastics fail to break down in ocean

It adds to existing evidence only natural fibers degrade in the marine environment.

Lead author Dr. Sarah-Jeanne Royer, of the University of California, San Diego, explained: "This study shows the need for standardizing 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."

Tests reported in the journal PLOS ONE were carried out off the long concrete Scripps Pier in northern La Jolla.

The team tracked the ability of natural, synthetic and blended fabrics to disintegrate directly in the Pacific.

In 2020, 367m tonnes of plastic were produced globally. Less than ten percent is recycled.

Beaches are littered with plastic bottles and wrappers. The stomachs of marine mammals are filled with fragments of plastic.

Plastic fishing nets dumped at sea can throttle unsuspecting animals. An expanse of water in the Pacific twice the size of France contains at least 79,000 tonnes of plastic.

Dr. Royer and colleagues found natural and wood-based cellulose fabrics degraded within a month.

Synthetic textiles, including so-called compostable plastic materials like polylactic acid (PLA), and the synthetic portions of textile blends, showed no signs of degradation even after more than a year submerged in the ocean.

An estimated 62 percent of textiles — 68 million tons — are now made from plastic fibers 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.

Bio-based plastics made from renewable natural resources such as cornstarch or sugar cane have been marketed as a potential solution to the plastic problem.

PLA is one such polymer in the bio-based plastics market, often labeled as biodegradable and compostable. The team chose this textile for the study given its extensive use as a replacement for oil-based materials.

Ten different types of fabrics were analyzed including 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 textile 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 about 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 high-resolution scanning of the chemical composition and molecular structure of the fibers. The samples were then submerged again, in a process that lasted for 231 days at the sea surface and 196 days at the seafloor.

The samples were later moved to the Experimental Aquarium at Scripps Oceanography and 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.

Dr. Royer said: "The natural, cellulose-based materials would disintegrate in about one month, so we would exchange for a new sample after the old one disintegrated. The natural samples were replicated five times, while the plastic samples remained the same for more than a year."

Further analyses showed the natural fibers became thinner with time, while the diameter of the plastic fibers remained the same showing no sign of biodegradation.

Senior author Dr. Dimitri Deheyn said: "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."

Given these results, the researchers hope consumers will become more aware of the power of their own choices. 

Dr. Royer said: "Consumers who are concerned about microfibre plastic pollution should be mindful of the materials they are buying.

"We should all aim to buy fewer garments, opt for high-quality, cellulose-based materials like cotton, merino or wool that will last longer, or look to more circular and sustainable options that repurpose items like clothing swaps and Buy Nothing groups."