Plastic and microplastic pollution of oceans is a wicked problem. Using bioinformatics and statistical analysis, scientist Victor Gambarini looked to correlate marine microbes that could degrade plastic with levels of plastic pollution.
This article has been republished from The Conversation under Creative Commons licence CC BY-ND 4.0 and is written by Victor Gambarini, a PhD Student in Marine Science, University of Auckland, Waipapa Taumata Rau. It was originally titled Most plastics are made from fossil fuels and end up in the ocean, but marine microbes can’t degrade them – new research.
Marine plastic pollution is a massive environmental issue, with a plastic smog of an estimated 170 trillion particles afloat in the world’s oceans. This highlights how urgently we need to develop strategies to mitigate this environmental crisis.
We know some microbes can break down certain plastics, but our new study finds no clear correlation between plastic pollution levels and the production of plastic-degrading enzymes by marine microorganisms.
To address this issue, we need to understand the varying properties and environmental impacts of different types of plastic.
Most plastics are not degradable
There are four main types of plastics: biodegradable, bio-based, fossil-based and non-biodegradable. The terms can be confusing and lead to misunderstandings about their environmental impact.
Biodegradable plastics can break down naturally through the action of living organisms such as bacteria. They are made from renewable sources such as corn starch or sugar cane and don’t linger in the environment for long periods. Examples of biodegradable plastics are polycaprolactone (PCL), polylactic acid (PLA) and polyhydroxybutyrate (PHB).
Bio-based plastics are also derived from natural materials such as plants. These plastics include polyethylene terephthalate (PET), which is widely used for clothing and containers for liquids and food. However, while PET can be made from renewable sources, most of its production is derived from fossil fuels.
Fossil-based plastics are made from oil and gas. They include common types like polyethylene (PE), which is used for single-use food packaging, and polyvinyl chloride (PVC), commonly used for water pipes and wire insulation.
These plastics are generally not biodegradable. They do not decompose naturally and can persist in the environment for centuries, contributing significantly to pollution and global warming.
PE is the most manufactured plastic type in the world. It accounts for 103.9 million metric tonnes (mmt) per year, followed by PET (65.4 mmt) and PVC (50.5 mmt). However, globally only 9% of all plastic waste is recycled.
According to Plastics NZ, terms such as “bioplastic”, “biopolymer”, “bio-based” and “biodegradable” are being used interchangeably, even though they signify entirely different things.
Ocean microbes cannot break down plastics
Our study analysed genetic information from microorganisms in the ocean, using data from hundreds of water samples collected during expeditions.
This provided us with insights about the genes marine bacteria use to make enzymes, including the one they use to degrade some plastics. We can then track which enzymes these microbes use at any given time.
The idea is that if marine microorganisms are breaking down plastics, they have to produce the enzymes capable of doing it. Therefore, if microbes are biodegrading plastics in our oceans, locations with more plastic pollution should have higher levels of enzymes for plastic degradation.
Our study found no clear global connection between plastic pollution levels in the ocean and the enzymes produced by marine microbes to degrade plastics. This suggests the ocean microbiome hasn’t evolved efficient mechanisms to break down various types of plastic.
There are several reasons for this. Plastics are very different and complex. Each type of plastic has its own structure and properties, and microbes might not have had enough time or pressure to evolve special enzymes for each type.
Environmental conditions such as temperature, currents and nutrient availability could also play a role in influencing microbial plastic degradation.
Overall, our findings suggest the global ocean microbiome has not yet evolved to efficiently degrade the many types of plastic pollution plaguing marine ecosystems. This highlights the ongoing danger plastic pollution poses for marine environments.
Developing solutions will likely require dramatically reducing new plastic waste, recovering existing ocean plastic and shifting to biodegradable plastic types.
While disappointing from an environmental remediation perspective, the lack of widespread microbial plastic degradation confirms the durability of synthetic polymers and highlights the vast challenge we face to clean up the oceans.
Nature of science – communicating in science
As new types of plastic materials enter the marketplace, care must be taken to use specific and accurate terms to denote how the materials behave, and how they can be dealt with at their end-of-use period.
Related content
Read more about Bioplastics and Microplastics and then explore How harmful are microplastics?
Learn about Oceans of rubbish, Plastics and recycling, Biodegradability, composability and bioplastics and The future of plastics: reusing the bad and encouraging the good.
Read the Connected article Down the drain to see how students in Petone, Lower Hutt, took action to prevent rubbish from entering their local marine environment.
Plastic is a wicked problem. It’s incredibly useful, but it’s also a huge environmental issue. Helpful PLD resources are Thinking about plastic – planning pathways, which includes our interactive planning pathway, and Material World – Recycling and biodegradability.
When we throw something away, how do we know where ‘away’ is? The Sustainable Seas National Science Challenge developed online tools to help us find out. Ocean Plastic Simulator is an interactive computer simulation that shows where plastic is likely to end up when it is dropped in the ocean.
New Zealand science organisations Royal Society Te Apārangi and the Office of the Prime Minister’s Chief Science Advisor created reports and resources to help us rethink plastic. Check out the interactive timeline. It gives a short history of plastic – including innovations and some of the impacts.
Explore alternatives to fossil fuel-based plastics in The ZESPRI biospife, Starch-based disposable plates and trays, Skateboards made out of harakeke? and Turning old into new.
Activity ideas
Explore biodegradability in the Biodegradability experiment or Testing the biodegradability of potato plates – where students can compare the rate of degradation of disposable plates using three different disposal methods.
In Make a composite material container students can develop their understanding of composite materials and how that a composite material has new and different properties when compared to the properties of the individual materials.
For activities based around reuse and recycling try: Plastic – reuse, recycle or rubbish game, DIY plastic recycling plant, Waste – a growing challenge! and Determining the properties of plastic and glass.
The What happens to our plastic bottles? activity is perfect for NZC levels 1 and 2. It uses the New Zealand Ready to Read books At the Beach and What Does the Tide Bring In? to introduce the PET plastic recycling process.
Citizen science projects
Bring some citizen science into the classroom with the local Litter Intelligence, Mizuiku Upstream Battle, Backyard Battle or the international project Litterati.
Useful links
Find out more about some of the research mentioned in this article:
The research explained in this article is from the paper Uncoupled: investigating the lack of correlation between the transcription of putative plastic-degrading genes in the global ocean microbiome and marine plastic pollution.
Understanding the amount of plastic particles in the ocean, where they are and how they move is part of the work to find solutions. Read more in: A growing plastic smog, now estimated to be over 170 trillion plastic particles afloat in the world’s oceans—Urgent solutions required.
Scientists, including the author of this article, are working on, PlasticDB: a database of microorganisms and proteins linked to plastic biodegradation. The database was a source of information for the work outlined in this article.
Chemical and biological catalysis for plastics recycling and upcycling, looks at different plastics and issues around recycling. The paper argues that developing catalyst-driven technologies for plastics deconstruction and upcycling is critical to incentivise improved recycling rates and the address the issue of plastic pollution.
The author used data from existing genetic analysis of water samples in his study. These samples were collected during other scientific expeditions and the subsequent analysis of the samples has created an archive of publicly available information. Learn more about the earlier collection and analysis work carried out between 2009 and 2013 by The Tara Océan Foundation.
Acknowledgements
This article was written by Victor Gambarini, a PhD Student in Marine Science, University of Auckland, Waipapa Taumata Rau. The article was originally published in The Conversation, June 2024. Read the original article.
