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Jul 315 min read

Microplastics – The threat polluting our environment

As we mark the end of another Plastic Free July, our Carnegie Trust funded project on microplastics in the Aberdeen Bay is kicking off. As part of this research, we will run a three part blog series outlining the microplastics in our environment written by research assistant Dayna Ledingham. This first post introduces what microplastics are and why they are a threat to our environment.


Introduction

Over the past few decades, the global production of plastic has skyrocketed, increasing from around 30 million tons in the 1960s to 140 million tons by the turn of the 21st century. As time passes, larger plastic items break down into tiny fragments known as microplastics, which are now accumulating in sedimentary systems across the globe. Alarmingly, there are now estimated to be at least 5.25 trillion pieces of plastic floating in the world’s oceans (Eriksen et al., 2014).


This growing presence of microplastics poses serious threats to marine ecosystems and human health. The problem has become so pervasive that scientists have declared the beginning of a new geological epoch called the Anthropocene, characterized by the prevalence of plastics and other man-made materials (Kane and Clare, 2019).


Much like studying natural sediments, understanding the distribution of microplastic particles can provide insights into their origins and histories This can help us to apply policies to reduce their prevalence in the environment. [RB1] But what exactly are microplastics, where do they come from, and why should we be concerned about them? These are questions this blog post aims to explore.

 

What are microplastics? (definition, shape, type, composition)

Plastics consist of carbon and hydrogen atoms bound around polymer chains. They come in from of Thermoplastics (PVC, PE, ABS and PP), Thermosetting plastics and Elastomers (rubber). More specifically microplastics (MPs) are defined as a particle of plastic that is under 5mm in size, whereas those above 5mm is defined as a macroplastic. Meanwhile under a nanometre in size is a nano-plastic. (Harris, 2020) (See fig. 1).


A classification of plastic litter sizes. Including nano, micro, meso, macro and mega. (What is microplastic? – Microplastic Research in Taiwan, no date).


For reference mud, which is a combination of silt and clay, is defined as 2 to  30 nanometres in size, whilst sand particles are 0.06mm to 2.0mm (1mm is equivalent to 1000000 nanometres) (Harris, 2020). There is however some debate as to where the nano- microplastic size boundary should be placed with some studies suggest 0.1 Nanometres (Klaine et al., 2012) and others suggest 20 nanometres (Wagner., 2014).

 

What about the shapes and types of microplastics? Microplastics come in all different shapes, as listed below (fig. 2):

  1. Pellets – Usually cylindrical or spherical and originate from industrial resin pellets.

  2. Fragments – The most occurring shape that comes in all shapes and colours. Originating from large plastic pieces.

  3. Film – Thin sheet plastics. Originating from foil, bags and other packaging materials.

  4. Foam – Any plastic with a foam structure. Such as PVC.

  5. Fibre- A fibrous plastic. Usually from the washing of clothes.


Fig.2 – Types of microplastics including fragments, pellets, film, foam and fibres. (What is microplastic? – Microplastic Research in Taiwan, no date)


Fibres are by far the most common microplastic found in the ocean. With a dominating value of 90% in beach environments. This is usually because they have a larger surface area and are less dense, so they take longer to settle and float on the sea for longer compared to other MP types (Harris, 2020).

 

Where do they come from? (primary vs secondary sources)

There are two main microplastic sources known as primary and secondary. Primary sources are microplastics that are manufactured to be 5mm or under, such as glitter or microbeads, commonly found in cosmetics. When larger plastic items break down over time to 5mm or under this is known as secondary microplastics, and they come in the form of films, fibres or fragments. There are lots of ways a large plastic item can break down such as washing of synthetic materials, tire wear on the road, chemical and UV degradation, biological degradation or physical abrasion. Plasticizers can also leach, causing the plastic to degrade quickly (Horton and Dixon 2018 ).

 

The most common source of secondary plastics is due to illegal dumping, incorrect waste management and accidental loss. A study on microplastic retention within soils found synthetic fibres from sewage sludge retained within treated agricultural soil (as fertilizer) up to 15 years after the last sludge application. This then gets naturally fed into rivers as runoff until it reaches the ocean. MPs can even travel through the air as road dust and fibres from synthetic materials (Horton. and Dixon 2018) (fig. 3).


Fig. 3 – A summary of microplastic sources and their percentage of distribution. (Microplastics is Bigger Problem than Expected, no date)

 

All this plastic always reaches the oceans one way or another through air, floods, rivers or runoff. This has been proved by several studies (fig 4).

Fig.4: (Horton. and Dixon 2018) An image showing the plastic ‘cycle’ and how microplastics eventually reach the ocean.

 
How do MPs interact with the environment?

Microplastics are known to be a huge concern for the ecosystem. Numerous deaths of whales, turtles and seabirds are reported every year due to plastics entanglement and consumption. Smaller aquatic animals such as zooplankton, small fish, mussels and crabs take physical damage through their gills and gut caused by clogging of microplastics. Sharper microplastics can cause internal lacerations leading to bacterial infections in the animal and eventually death. Larger predators ingest the microplastic-infested smaller animals thus concentrating microplastics in their own bodies. This has a knock-on effect on the food web (Horton and Dixon 2017) (fig 5).


Fig. 5 – Microplastics entering the food chain and its impact (Microplastics from primary and secondary sources enter the food chain... | Download Scientific Diagram, no date)

 

Additionally, as humans, we inhale and ingest microplastics regularly, including through the ingestion of seafood. The pollution of microplastics is global and certainly looking at how the plastic is transferred from its source can help drive policy makers to find a solution to contain it.


--- Keep exploring ---

 

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