Biodegradable plastic materials do not biodegrade in the ocean

Plastic pollution has insidiously infiltrated nearly every aspect of modern life. The material is ubiquitous, not only in the obvious form of bags, cups, and bottles, but it also finds application in clothing, rugs, and other textiles.

A recent study from the Scripps Institution of Oceanography at UC San Diego has, for the first time, embarked on a mission to explore the ability of natural, synthetic, and blended fabrics to biodegrade in the ocean. 

The paper, published in the journal PLOS One, exposes some unsettling truths about the persistence of plastic material in our marine environment.

An accidental experiment

Sarah-Jeanne Royer, the study’s lead author, ventured beneath the Ellen Browning Scripps Memorial Pier for an enlightening experiment. There, she discovered that natural and wood-based cellulose fabrics dissolved into nothingness within a month. 

However, synthetic textiles like compostable plastic materials, including polylactic acid (PLA), and the synthetic parts of blended fabrics showed no degradation signs even after over a year underwater.

“This study highlights the need for a more standardized way to evaluate materials marketed as compostable or biodegradable,” explained Royer, a former postdoctoral scholar in the Dimitri Deheyn lab at Scripps Oceanography. 

“What might break down in an industrial setting does not necessarily degrade in the natural environment, eventually becoming a marine and environmental pollutant.”

Implications of humans’ increasing demand for plastics

The larger implications of this plastic consumption are devastating. Stark images from Chile and Kenya display towering landfills bursting with discarded clothing, stark illustrations of fast fashion’s global footprint. 

With an estimated 62 percent of textiles – approximately 68 million tons – being manufactured from plastic fibers and blends, these materials could persist in our environment for centuries. Adding to this issue, synthetic textiles shed plastic microfibers during regular wear and washing, which can bypass most washing machines’ filters and end up in our oceans.

The team also considered bio-based plastics, often touted as an eco-friendly alternative to traditional plastics. These materials, derived from renewable resources like cornstarch or sugar cane, are increasingly finding use in place of oil-based materials. PLA, a polymer widely used in the bio-based plastics market and frequently labeled as biodegradable and compostable, was a prominent component of the study.

How the research study was conducted

The researchers used ten different types of fabrics for their experiment, including wood-based cellulose, natural cellulose, bio-based plastic, oil-based plastic, and fabric blends. All of these are staples in the textile industry and find uses in everything from clothing to carpets, packaging materials, and disposable medical textiles such as masks.

Textile samples underwent rigorous testing at both the sea surface and the seafloor in flow-through containers. This process involved weekly inspections, high-resolution electron microscopy, and Raman spectroscopy over several months.

The experiment’s findings were consistent: natural, cellulose-based textiles repeatedly broke down in 30-35 days, while oil-based and bio-based materials stubbornly resisted any form of disintegration, even after a total of 428 days.

“Natural, cellulose-based materials would disintegrate in about a month,” Royer pointed out. “The natural samples were replaced five times, while the plastic samples remained unchanged for more than a year.”

Senior author of the study and Scripps marine biologist, Dimitri Deheyn, employed electron microscopy to measure each fiber’s size and structure. He noticed that natural fibers got thinner over time, while plastic fibers stubbornly retained their diameter, showing no signs of biodegradation.

Study co-author Francesco Greco conducted the Raman spectroscopy analysis. Currently at the Weizmann Institute of Science, he observed significant alterations in the cellulose-based materials’ chemical fingerprint while the bio- and oil-based plastics showed no change.

Degradation behavior documented

Blended fibers, often marketed as a sustainable alternative to fully synthetic textiles, contain interwoven strands of natural fiber and bio- or oil-based plastic. However, the study demonstrated that only the natural part of these blends degraded, leaving the plastic portion stubbornly intact.

This degradation behavior was confirmed by testing in a closed-system bioreactor, which mimics a marine environment. An independent company conducted this testing, measuring the amount of carbon dioxide produced by microbial activity as a proxy for biodegradability. 

Just like in the ocean, the cellulose-based materials showed complete biodegradation within 28 days, whereas the oil-based and bio-based fibers remained unchanged.

What the research team learned

The researchers concluded that both bio-based polylactic plastic, which is marketed as environmentally friendly, and oil-based plastics, such as polyethylene terephthalate and polypropylene, are significant sources of human-caused pollution. Therefore, more work is needed to understand the fate of these materials in a natural environment.

Deheyn underscored the need for accurate language when talking about 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 findings, Royer and her team hope consumers will better understand the impact of their purchasing decisions.

“Consumers who are concerned about microfiber plastic pollution should be mindful of the materials they are buying,” Royer advised. “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.”

The research was supported by the Biomimicry for Emerging Science and Technology (BEST) Initiative from the Deheyn lab, contributions from Lenzing, The Walter Munk Foundation for the Oceans, and Preserve Calavera, and the Young Thousand Talents Plan of China.

The study lays bare the stark reality of plastic pollution and provides a strong impetus for rethinking our textile consumption practices.

More about plastic pollution

Plastic pollution has become a profound environmental issue, affecting both terrestrial and aquatic ecosystems worldwide. Despite being a versatile, durable, and cost-effective material, plastic’s resistance to natural degradation processes poses severe threats to the environment and human health.

Environmental Impact

Marine Pollution

Plastics are the primary constituents of marine debris. Every year, millions of tons of plastic waste, including bags, bottles, fishing nets, and microbeads, enter the ocean, causing significant harm to marine life. Animals can become entangled in this debris or mistake it for food, leading to physical harm, starvation, and often death.

Microplastics

These tiny plastic particles, often less than 5mm in diameter, result from the breakdown of larger plastics or are intentionally manufactured for use in personal care products and industrial processes. They easily infiltrate ecosystems and are ingested by a wide range of organisms, leading to potential physical and toxicological effects.

Soil Pollution

Discarded plastic products and microplastics can also infiltrate terrestrial ecosystems, polluting soil and impacting both plant growth and soil organisms.

Air Pollution

When burned, plastic waste releases toxic gases like dioxins, furans, mercury, and polychlorinated biphenyls into the atmosphere, contributing to air pollution and climate change.

Human Health Impact

Toxic Chemicals

Many plastic products contain chemical additives like phthalates, bisphenol A (BPA), and polybrominated diphenyl ethers (PBDEs) to improve their properties. However, these chemicals can leach out over time, especially when heated or in contact with food. Ingesting these chemicals has been linked to various health concerns, including hormone disruption, developmental issues in children, and an increased risk of certain cancers.

Food Chain Contamination

Microplastics and the associated toxic chemicals can accumulate in the food chain. When smaller organisms contaminated with microplastics are consumed by larger predators, these toxins can biomagnify, posing a potential risk to human health when consuming affected seafood.

Airborne Microplastics

Recent studies have shown that microplastics can become airborne, representing a potential inhalation risk. The health implications of this exposure route are still under investigation.

Waste Management

Inadequately managed plastic waste can serve as breeding grounds for disease vectors such as mosquitoes, leading to the spread of diseases like malaria and dengue.

To mitigate the impacts of plastic pollution, efforts are being made to reduce plastic production and consumption, promote recycling, develop biodegradable alternatives, and clean up existing plastic waste. 

Public awareness and changes in behavior, in combination with effective policy and technological innovation, will be critical in addressing this global environmental challenge.

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