Biodegradable plastic substitutes under scrutiny: What really happens in ocean waters?
The persistent accumulation of waste from petroleum-based plastics in our oceans is a serious environmental issue that threatens marine life. Items made from plastic, such as water bottles, can endure for decades in the ocean, retaining their original form. Even when they finally break down into microscopic pieces, known as microplastics, they don't biodegrade. Instead, they remain as indigestible pollutants that accumulate in food chains.
3:22 AM EST, January 17, 2024
Over the past few years, substitutes for the commonly used petroleum-based plastics have developed. Introducing these substitutes aims to cut down the dependency on fossil fuels for plastic production and ensure environmentally friendly waste.
Polylactic acid (PLA), a polymer of lactic acid derived from fermented sugars and starch, is one of the most commonly used substitutes for plastics. PLA is able to break down into lactic acid at high temperatures, which can often be found in large compost stacks. Still, this reaction is neither consistent nor efficient under cooler conditions.
Latest research on the degradation of biodegradable materials
Sarah-Jeanne Royer and her team from the Scripps Institution of Oceanography at the University of California in San Diego led research (DOI 10.1371/journal.pone.0284681) focused on the decomposition of biodegradable materials. The researchers placed samples of PLA, alongside samples of petroleum-based materials, cellulose-based materials, and a mix of cellulose and petroleum, into cages in the ocean off the coast of La Jolla, California. The samples were assessed weekly for decomposition indications and submerged back in the ocean after several hours.
Interestingly, cellulose-based material decomposed speedily in less than a month. Lab chemical analysis determined that the cellulose breakdown resulted from biological processes, producing CO2, and not simply due to mechanical wear and tear. In contrast, the petroleum-based material, the mixed material, and the PLA showed no degradation, even after 14 months of study.
"Our findings demonstrate that 'compostability' does not mean degradation in natural conditions," says Royer. "Labelling compostable plastics as biodegradable can mislead people, as it may suggest that the material degrades within the environment. PLA-based plastics must be composted under appropriately regulated conditions to live up to their potential as biodegradable substitutes for petroleum-based plastics."
A call for new standards in plastic testing
"This study marks one of the rare groundbreaking explorations comparing the biodegradability of different types of materials (natural, fully synthetic, and biological) under natural and controlled environmental conditions. Our findings highlight the necessity for standardized tests to validate whether materials marketed as compostable or biodegradable, like PLA, actually degrade under natural environmental conditions. It's essential that consumers, particularly those concerned about microfiber plastic pollution, are well-informed and aware of the materials they are purchasing."
