Shape matters: Research at Lassonde explores how microplastic transport is impacted by varying shape

Microplastics are tiny particles causing concern across the globe due to risks they pose to human health and the environment. Understanding the behaviour of these particles is crucial for the development of monitoring tools like air quality models, which help provide accurate information about atmospheric conditions and inform strategies to mitigate the impact of microplastic pollution.

“Microplastics are showing up in impossible-to-reach places, as far as artic regions, and we want to know how these particles are being transported to such remote locations,” says Mark Gordon, associate professor in the Earth & Space Science & Engineering Department at York University’s Lassonde School of Engineering. “One idea we have is that shape may have a significant impact on the way these particles travel.”

Through ongoing research, Professor Gordon and Ronald Hanson, associate professor in the Mechanical Engineering Department, are working collaboratively and applying their distinct expertise to answer the question, ‘does shape matter?’

“It’s easy to assume that all particles are spheres, but microplastics aren’t one uniform shape,” explains Professor Hanson. “They are very interesting particles with twists and turns and different sizes. Think about miniature shards off tires or tiny pieces of fabric threads.”

Initiating this research, Professor Gordon recently published a paper that investigates the deposition and trajectory of different sizes and shapes of microplastics using a model called HYSPLIT. This work was led by his former MSc student, Eric Ward, who committed many hours to number crunching and complex calculations, exploring the diverse behaviours of uniquely shaped microplastics.

Results of this study showed that irregularly shaped microplastics, specifically those larger than six micrometers, exhibit significantly different behaviour than common, sphere-shaped particles. In fact, some of the uniquely-shaped microplastics were deposited over an area that was 32 percent larger than that covered by similarly sized sphere-shaped particles.

This research serves as a starting point for future work that can support the development of more accurate air quality models, by incorporating information about the behaviour of different shapes of microplastics.

Complementary to this research, Professor Hanson is working on various hands-on experiments to help establish the best parameters for representing microplastics of varying shape in air quality models.

“We are looking at how we should be modelling microplastics, what information we should put into these systems and how accurately models reflect real world data,” he explains.

Specifically, Professor Hanson worked with his PhD student, Amirhossein Hamidi and former MASc student, Daniel Daramsing to investigate how straight and cylindrical rod-shaped microplastics behave during transport and deposition. Together, they designed an experiment which involved dropping tiny rods into a solution of water and glycerine, to simulate microplastic transport. Images of this activity were captured using specialized cameras and analyzed with their custom-built software.

“Through laboratory experiments, we were able to study the activity of different shaped rods and apply mathematical calibrations to determine their trajectory,” he says.

Among many findings, results from these experiments demonstrated that curved cylindrical rods settle much faster than straight rods, and curvature has a direct impact on the speed at which rods fall.

Not only did this project provide insight into the behaviour of rod-shaped microplastics during transport, but it also helped establish a usable model that can predict specific properties of microplastic fibers in the atmosphere.

So, does the shape of microplastics matter? According to the research of Professors Gordon and Hanson – it probably does.

In support of future work, the duo is hoping to recruit additional student researchers and further explore how air quality models can be enhanced by incorporating the behaviour of uniquely-shaped microplastics. This initiative aims to support scientific research advancement, while contributing to the development of practical solutions for a sustainable world, by improving methods for accurate monitoring and control of microplastic pollution.