Are biodegradable plastics the solution to the plastic crisis?

by Pauline Hughes, Contributing Writer

As you make efforts to be a more environmentally-conscious consumer, labels like ‘biodegradable,’ ‘compostable,’ ‘sustainable,’ ‘green’ and ‘environmentally-friendly’ can get your head spinning. With growing concerns for plastic pollution in particular, it’s very likely that you’ve encountered such words on plastic products in your day to day life.

According to the Government of Canada, Canadians generate more than 3 million tonnes of plastic waste every year. Once no longer in use, plastic can either be recycled, disposed of in landfills, incinerated, or littered. Although we hope that the majority of these plastics are being recycled, it is estimated that only about 9% are (1). The rest can be considered waste. Worse still, plastics that enter the environment risk causing harm to wildlife and human beings. Thus, the improper disposal of plastics poses an immense threat to ecosystems and human health.

Attempts to mitigate this plastics waste management crisis have led to the introduction of alternative types of plastic to the market. For instance, products made from biodegradable plastics are becoming more common in stores. While conventional plastics break down very slowly, biodegradable plastics offer the advantage of degrading on a much shorter time scale.

First and foremost, it is important to clarify what is meant by ‘biodegradable’ because the extent to which a material like plastic degrades has important consequences for the environment. According to the International Union of Pure and Applied Chemistry (2012), a material is considered ‘biodegradable’ if it can be broken down by the enzymatic processes of living organisms like bacteria, fungi and algae (2). While the term does not specify the time scale or conditions under which biodegradation must take place, there are various industry standard specifications used to classify the ‘biodegradability’ of materials (3). Standardized tests assess factors such as the percentage of degradation achieved within a specified time-frame, the temperature and the environment of the disposal site (e.g. soil, seawater) (4).

Plastics are synthetic materials composed of polymers, which are large molecules made up of repeating subunits (5). They have many properties that make them desirable for various uses: they are flexible, light-weight, resistant to corrosion, have low thermal and electrical conductivity (4,6). Conventional, non-biodegradable plastics are typically fossil-based, made from petroleum or natural gasses. Meanwhile, biodegradable plastics fall into two broad categories: bio-based and petroleum-based. Among these biodegradable plastics, bio-based ones attract more attention from the public as they are derived from renewable resources (7). The most common bio-based biodegradable plastics, PHAs and PLAs, are produced by the bacterial fermentation of sugars (4). It’s also important to note that not all bio-based plastics are biodegradable; these non-biodegradable plastics made from biomass are often chemically identical to conventional plastics (4,5).

All types of plastic degrade to some degree due to physical and chemical processes. However, conventional plastics can’t be broken down completely from these processes and form microplastics (4). Biodegradable plastics, on the other hand, can completely decompose into water, CO₂ and biomass by microorganisms, given the right conditions. Still, without the proper conditions favoring biodegradation, biodegradable plastics can also form microplastics.

Several factors influence how easily a biodegradable plastic breaks down. Among these are the size and shape of the plastic, the chemical structure and crystallinity of the polymers, and the environmental conditions of its degradation (4,6). In order to degrade completely, biodegradable plastics should be treated in industrial compost facilities with certain microbial populations and temperatures of 58ºC or more, depending on the classification of biodegradability based on industry standard specifications (4). 

Biodegradable plastics offer many of the same properties of conventional plastics with the added benefit of being biodegradable and are thus used primarily for short-lived items such as food packaging, single-use cutlery, water bottles, straws, and bags. The hope is for the use of these biodegradable plastics to help divert waste from already overwhelmed landfills. Moreover, the production of biodegradable plastics may release less CO₂ as they’re made from using biomass instead of fossil materials (7). 

While biodegradable plastics offer some advantages over conventional plastics, they are far from being a perfect solution. For instance, producing bio-based biodegradable plastics requires sugars from food crops like corn and sugarcane. Thus, land and water resources have to be allocated to their production, competing with food crops (4). 

Additionally, the proper disposal of biodegradable plastics is imperative to their potential benefit. If these plastics are left to degrade in landfills under anaerobic conditions, methane, a potent greenhouse gas, is produced as they decompose (8) and if they are incinerated, the carbon within them is released into the atmosphere as CO₂ (6). Moreover, a recent study found that after a three-year period, biodegradable plastic bags left to deteriorate buried in soil and submersed in a marine environment were still mostly intact and functional, carrying items without breaking. Meanwhile, bags left in the open-air fragmented into microplastics after three years (9). Under the right conditions for biodegradation, these intact bags and microplastics could be broken down further, but their sustained presence in these natural environments could still cause harm.

With so many factors at play, from production to proper disposal, it becomes difficult to conclude whether biodegradable plastics will have an overall positive or negative effect on the environment. Of course, the best option would be to reduce our dependence on single-use materials altogether. Nonetheless, biodegradable plastics still hold potential as a more sustainable alternative to conventional plastics. So look out for labels reading “biodegradable” on plastic items, and be sure to find the right bin for them too!

Edited by Autumn Pereira

References:

1. Government of Canada. (24 December 2021). “Plastic waste and pollution reduction”. Retrieved from https://www.canada.ca/en/environment-climate-change/services/managing-reducing-waste/reduce-plastic-waste.html
2. Vert, M., Doi, Y., Hellwich, K., Hess, M., Hodge, P., Kubisa, P., Rinaudo, M., & Schué, F. (2012). Terminology for biorelated polymers and applications (IUPAC Recommendations 2012). Pure and Applied Chemistry, 84(2): 377–410. doi:10.1351/PAC-REC-10-12-04.
3. United Nations Environment Programme. (2021). From Pollution to Solution: A global assessment of marine litter and plastic pollution. Nairobi. Retrieved from https://wedocs.unep.org/bitstream/handle/20.500.11822/36963/POLSOL.pdf
4. Filiciotto, L., & Rothenberg, G. (2020). Biodegradable Plastics: Standards, Policies, and Impacts. ChemSusChem, 14(1), 56-72. https://doi.org/10.1002/cssc.202002044
5. Geyer, R. (2020). Production, use and fate of synthetic polymers in plastic waste and recycling. In Plastic Waste and Recycling: Environmental Impact, Societal Issues, Prevention, and Solutions. Letcher, T.M. (ed.). Cambridge, MA: Academic Press.13-32. Retrieved from https://www.researchgate.net/profile/Mohanraj-Chandran/publication/339905534_Conversion_of_plastic_waste_to_fuel/links/5e982e474585150839e08d12/Conversion-of-plastic-waste-to-fuel.pdf
6. Zhu, J., & Wang C. (2020). Biodegradable plastics: Green hope or greenwashing? Marine Pollution Bulletin, 161(December 2020). https://doi.org/10.1016/j.marpolbul.2020.111774
7. Moshood, T.D., Nawanir, G., Mahmud, F., Mohamad, F., Ahmad, M.H., & AbdulGhani, A.. (2022). Sustainability of biodegradable plastics: New problem or solution to solve the global plastic pollution? Current Research in Green and Sustainable Chemistry, 5(May–June 2022). https://doi.org/10.1016/j.crgsc.2022.100273.
8. Song, J. H., Murphy, R. J., Narayan, R., & Davies, G. B. (2009). Biodegradable and compostable alternatives to conventional plastics. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 364(1526), 2127–2139. https://doi.org/10.1098/rstb.2008.0289
9. Napper, I. E., & Thompson, R. C. (2019). Environmental Deterioration of Biodegradable, Oxo-biodegradable, Compostable, and Conventional Plastic Carrier Bags in the Sea, Soil, and Open-Air Over a 3-Year Period. Environmental Science & Technology, 53(9), 4775-4783. https://doi.org/10.1021/acs.est.8b06984

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