Breaking Down Plastics: Oxo-degradation and microplastics
Have you ever read OXO-DEGRADABLE in a plastic bag?
This label on the bags may make you think that this is a special type of plastic bag that will magically disappear without leaving a harmful trace.
Oxo-degradation was a novel technique designed to rapidly disintegrate plastic materials, which sounds like a solution to the problem, right?
Let's recap what plastics are.
Plastics are polymers, which is the technical way of saying that their molecular structure is an ordered set of small repeating molecules, called monomers (unitary structures). The joining of these units creates an internal structure that gives plastics properties such as flexibility and strength. Each plastic (PET, polystyrene, polyester, etc.) has a different molecular structure.
Oxo-degradation, also known as oxidative degradation or photo-oxidation, is a chemical process that occurs in certain polymers, particularly plastics, when exposed to oxygen and/or sunlight (UV rays). This triggers the degradation of polymer chains through oxidation, leading to the breakdown of the polymer into smaller fragments.
The original patent for oxo-degradation was filed in the 1970's by Michael Stephen of the British company Symphony Environmental Technologies. The patent was titled "Degradable Plastics" and was filed in 1977. Since then, the technology has been licensed to other companies for use in a variety of applications.
Initially, oxo-degradable materials were thought of as a solution to the plastic waste problem. They were marketed as a way to reduce the waste and environmental impact of plastics by making them degrade faster. However, the use of oxo-degradable plastics has been controversial.
To understand the difference between degradation and biodegradation, see this link.
Oxo-degradable plastics break down into very small pieces (less than 5 millimeters in length) called microplastics, but instead of helping to solve the plastic pollution crisis, they are causing new damage to the environment.
This is because they are ingested by animals that mistake them for food and therefore integrate into ecosystems in a direct way. From microscopic plankton in lakes and oceans, through fish, turtles, and birds [1] to large mammals, such as whales.
Microplastics (and plastics in general) are seen by animals as food, killing them as they accumulate in their intestines. In addition, the additives used to make oxo-degradable plastics can also be harmful to the environment and leach into the soil and water.
Some facts about microplastics:
- A study published in Environmental Science & Technology estimates that up to 236,000 metric tons of microplastics from washing synthetic fabrics, such as polyester, are dumped into the ocean each year [2].
- Microplastics have been found in a wide variety of marine life, from small zooplankton to large whales. According to a study published in the journal Scientific Reports, more than 50% of sea turtles worldwide have ingested plastic debris [3]
- Microplastics have also been found in drinking water. A study commissioned by the World Health Organization found microplastics in tap water samples from around the world [4].
- Research in Environmental Science and Technology on oxo-degradable plastic bags concluded that none of the bags degraded completely in all environments and that oxo-biodegradable bags fragmented into microplastics that persisted in soil and marine sediments [5].
In addition, oxo-biodegradable plastics can contaminate recycling systems for other plastics by containing chemicals that are difficult to identify at recycling centers.
In response to these concerns, several countries in Europe have taken steps to ban or restrict the use of oxo-degradable plastics. In 2019, the European Union enacted a directive banning the use of oxo-degradable plastics in the EU, citing concerns about their environmental impact. Other countries, including France, Italy and the United Arab Emirates, have also implemented bans or restrictions on the use of oxo-degradable plastics.
Overall, while oxo-degradable plastics were initially seen as a promising solution to the plastic waste problem, their use has become increasingly controversial due to concerns about their environmental impacts. As more research is conducted on the long-term effects of these materials, we are likely to continue to see increased regulation and scrutiny of their use.
References:
- Blakemore,Erin (2015) 90 Percent of Seabirds Have Eaten Plastic. Smithsonian Magazine Online https://www.smithsonianmag.com/smart-news/90-percent-seabirds-have-eaten-plastic-180956484/
- Napper, I. E., & Thompson, R. C. (2016). Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions. Environmental Science & Technology, 50(11), 6257-6264.
- Schuyler, Q. A., Wilcox, C., Townsend, K. A., Wedemeyer-Strombel, K. R., Balazs, G., & van Sebille, E. (2014). Risk analysis reveals global hotspots for marine debris ingestion by sea turtles. Scientific reports, 4(1), 1-8.
- World Health Organization. (2019). Microplastics in drinking-water. World Health Organization.
- Environmental Deterioration of Biodegradable, Oxo-biodegradable, Compostable, and Conventional Plastic Carrier Bags in the Sea, Soil, and Open-Air Over a 3-Year Period Imogen E. Napper and Richard C. Thompson Environmental Science & Technology 2019 53 (9), 4775-4783 DOI: 10.1021/acs.est.8b06984
