Microplastic Basics

“Plastic is great, until we no longer need it” - Mr Lertrattanachaikij

Introduction


Plastic is a synthetic material commonly used in various sectors ranging from agriculture to healthcare and is an integral aspect of our everyday lives. Plastics' elasticity, durability, and lifespan have become their most advantageous and yet damaging traits to the ecosystem when it comes to plastic’s biodegradability. This issue has become a significant concern for Thailand since the 1980s, when surges in plastic use and the corresponding waste were recorded in Asian countries (Ng et al., 2023.) Waste mismanagement has only exacerbated this problem, with incineration and landfilling being the most common methods of plastic disposal (Ng et al., 2023.) Since then, Thailand has become one of Southeast Asia's top five largest plastic producers of municipal solid waste, producing roughly 1.14 kg/capita/day worldwide as stated by a 2021 study (Ng et al., 2023.) To further examine this subject, this section aims to provide an overview of plastic and its history, harmful effects, structure, and future.

History of Plastics


In the history of inventions, plastic has not been around for very long, and yet, it has dramatically shaped our modern world today and people's livelihoods, for better and worse. The first plastic, known as bakelite, was synthesised by Dr. Leo Baekland in 1907 through experimentation with phenolic resins (Walker, 1994) It was not until the 1950s where people began to realize that plastics’ durability and lifespan gave it potential to be used in packaging, construction, and manufacturing, causing plastic production to increase over time. With plastic production drastically increasing from 2 million tons annually to 381 million tons in 2015. As a result, the amount of plastic waste generated has grown to over 400 million tons annually (UNEP, 2024.) Owing to the high utility of plastics, it is a key product of the packaging and construction sectors, among others, that make up the plastic industry as can be seen in Figure 1. Yet, its environmental impact has long raised questions about its benefits.

Of course, it is important to note that plastic is not harmful in every context. For starters, plastic is light, durable, elastic, and possesses long-lasting properties that have allowed it to be effectively applied in various sectors ranging from farming to healthcare. The issue then is the disposal of plastic and its varying service life, which inevitably leads to the widespread presence of plastics as a pollutant. To illustrate this issue, a 2022 study (Oktavilla, 2020)compared plastic waste generation between the two largest producers of plastics: the packaging industry, 146,000,000 tons, and the construction industry, 65,000,000 tons (Oktavilla, 2020).Despite both sectors being the two largest plastic producers, in the construction industry, only 20% of the plastic produced by the construction sector (13,000,000 tons) became classified as waste, while 97% of all plastic produced by the packaging sector (65,000,000 tons) became classified as waste. This difference in the amount of plastic disposed of can be attributed to the service life of the plastic, as the packaging industry often designs its plastics to only be used once. In contrast, the construction industry designs its plastics to be used for years. This example shows that plastics are an essential part of the world that humans cannot live comfortably without–the only solution to counteract the continual production of plastic waste is to develop more effective plastic processing methods.

fig.1
Fig. 1 Primary plastic production by industrial sector(Oktavilla, 2020)

PET


Plastics are polymers, and the different types of plastics arise from the different monomers that make up these polymers. In general, polymers are defined as macromolecules made up of multiple repeating units, referred to as monomers. It is important to note that “polymer” is a general term and is not synonymous with “plastic,” in the same way that all squares are rectangles but not all rectangles are squares. The general structure of plastic–long chains of polymers held together by London dispersion forces–results in characteristics such as high malleability, high tensile strength, durability, insolubility in water, and resistance to corrosion (Shrivastava, 2018). Depending on the monomeric unit of the plastic, these characteristics may vary–some plastics are more flexible, some are stronger–however, durability remains a common quality for plastics in general.

Polyethylene terephthalate, commonly known as PET, is a heteropolymer of the polyester family composed of ethylene glycol and terephthalic acid monomeric units(Daubeny et al., 1954). It is a specific type of plastic polymer with the chemical formula (C10H8O4)n (Amanna et al., 2021). Most commonly encountered in the form of a plastic water bottle, PET plastics make up 12% of global solid waste (Benyathiar et al., 2022).

fig.2
Fig. 2 The Monomer of Polyethylene Terephthalate Plastic (Balamurugan et al., 2021)

This structure of PET polymers gives it the properties of high malleability, tensile strength, and durability, as well as insulating capacity (Amanna et al., 2021). Once again, this contributes to the long lifespan of plastics, including PET plastics. As PET plastic products ended up in landfills, certain bacteria, namely Ideonella sakaiensis, were discovered to have the ability to decompose those plastics into monomers via the enzyme polyethylene terephthalate hydrolase (PETase) (Yoshida et al., 2016).


The Big Problem–What are Microplastics?


The durable quality of plastics have greatly affected the material’s biodegradability especially when they are degraded into smaller sizes. Microplastics is a term used to refer to plastic particles that are less than 5 millimeters in size (Golmohammadi, 2023). There are two main types of microplastics: primary microplastics and secondary microplastics. Primary microplastics are plastics that have been intentionally manufactured to be less than 5 millimetres in size often found in cosmetic products. In comparison, secondary microplastics are plastics that have unintentionally degraded to be less than 5 millimetres in size through erosion or other means (Galafassi, 2019).

Microplastic fragments pose a significant threat to the environment, with the food chain in particular being an area of significant concern. Microplastics typically enter the food chain by being absorbed by plants–often absorbed through the roots and translocated throughout the plant–which are consumed by other organisms and as such travel through the trophic levels (Tang , 2023). The prevalence of microplastics in aquatic environments, especially the ocean, has also led to the introduction of microplastics into the food chain via the fish that consume them. Ingestion of microplastics from contaminated food sources cause harm to people through gastrointestinal obstruction, asthma, allergy, and chronic pneumonia [source bottom], to name a few. Furthermore, recent research has reported the presence of high accumulations of micro and nano plastic particles in deceased brains with documented dementia diagnosis (Nihart, 2025), hinting at a potential link between dementia and the amount of microplastics in the body.

Additionally, government action to manage and limit waste has also been rather ineffective. In an interview with Dr. Wijarn, president of the Thailand Environmental Institute, it was revealed that Thailand lacks any country wide waste management policy; instead loosely passing over responsibility to provincial authorities who oftentimes overlook the issue.

Combatting Microplastics


Microplastic pollution is an increasingly widespread and threatening concern, in not only Thailand, but also across the globe. In 2018, up to 360 million tonnes of plastic were produced globally compared to just 299 million tonnes in 2013, which is an increment of 20% in only 5 years time. (Ng et al., 2023) Microplastics can also impose risks on ecosystems, which can be seen through its entrance into the food chain, or through the deterioration of the fertility of soil from atmospheric deposition/degradation of large plastics (Leslie et al., 2022). Conventional methods of plastic waste management, like landfilling, incineration, and mechanical recycling, are insufficient for a growing population which comes in hand with an increase in plastic waste production. This is particularly a concern for microplastics that may pass through filtration systems unfiltered as a result of their small size and widespread dispersion.

In this context, enzyme-catalysed degradation is an emerging and sustainable approach to address microplastic pollution. PETase, an enzyme derived from Ideonella sakaiensis, can hydrolyse PET into monomeric components under environmentally and optimally controlled conditions (Yoshida et al., 2016). Recent advances in protein engineering and guided mutagenesis have enhanced PETase’s catalytic efficiency and thermostability under broader environmental conditions (Lu et al., 2022). The Thailand-RIS team aims to build on these developments by engineering a synthetic biological system using a plant chassis capable of expressing and optimising PETase activity to degrade microplastics. By doing so, we intend to develop a scalable platform for real-world applications in the future, as this approach of using a plant host and compartmentalised enzymatic systems not only allows us to reverse the microplastic pollution but also promotes the circular economy through the potential recovery of PET monomer that can be used for repolymerization.

Our project provides a renewable alternative to decomposing microplastics in the environment through utilizing plants. Choosing plants to inject the PETase will indirectly decrease carbon dioxide emissions in the atmosphere, since plants absorb carbon dioxide during photosynthesis, which will act against the rising problem of global warming. Working with plants is also effective due to their size and visibility to the naked human eye. Next, the highest frequency of polymers found in the soil environment globally include polyethylene plastics, followed by polyethylene terephthalate, PET, plastics (Zrimec et al., 2020). Therefore, due to the introduction of our Nicotiana benthamiana plant with PETase, PET plastics, which are prevalent in the rhizosphere, will greatly reduce in quantity and undergo decomposition. This will reduce its probability of uptake by other plants from the soil and consumption by predators, disallowing microplastics to enter the food chain or ecosystems, and harm human health.

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