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Microplastics: What’s the Latest Research?

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On April 22, millions of people around the world recognize Earth Day. Each year, Earth Day offers everyday people the opportunity to recognize the importance of environmental conservation and take action through various events and local sustainability initiatives.

The theme of Earth Day 2024 is “Planet vs Plastics” – a theme chosen to highlight the dangers of plastic pollution and to demand a dramatic reduction in the production of plastics over the next decade.

One aspect of plastic pollution that is receiving increased attention is the issue of microplastics. These tiny fragments of plastic waste – measuring less than 5 millimeters across – can be formed by almost any process that involves plastic and have already spread to contaminate huge swathes of the globe.

The study of microplastics and their potential threats to human and environmental health is still in its infancy. Here, we highlight some of the latest advancements in microplastics research, from their potential health impacts to the pursuit of a plastic-free future. 

How are microplastics formed and spread?

Understanding the sources of microplastics and how they spread is an important area for environmental research.

“I think most people think the source of microplastics is litter that breaks down — it doesn’t really biodegrade to much extent; it just fragments into smaller and smaller pieces as it gets weathered by sunlight. But we also find a lot of fibers that are most likely being shed from the synthetic clothing that we're wearing,” Dr. Matthew Ross, an assistant professor in the Department of Physical Sciences at MacEwan University, previously told Technology Networks.

Another often overlooked source of microplastics in the environment is car tires. As vehicles drive, tiny flecks of synthetic rubber polymers are shed from the tires as they rub against the road surface. These tire wear microparticles can be easily washed off of a road surface and flood into local environments when it rains.

“Stormwater runoff, which contains a mixture of sediment, chemical, organic and physical pollutants, is a critical pathway for microplastics to washed off from urban environments during rain and into local aquatic habitats. But to date, our knowledge of the amount of microplastics in urban stormwater, particularly tyre wear particles, is limited, as is the potential strategies we can use to minimise this source,” said Dr. Shima Ziajahromi, a research fellow at the Australian Rivers Institute.

In a recent paper published in Environmental Science & Technology, Ziajahromi and her team analyzed stormwater and sediment samples collected near constructed wetlands during rain storms. They found that approximately 19 out of every 20 microplastics collected were tire wear particles, at concentrations anywhere from 2 to 59 particles per liter of water.

The high prevalence of these plastic microparticles is an issue of “high concern”, according to researchers from the University of Exeter and the University of Plymouth. In their latest study, published in the Journal of Hazardous Materials, the joint research team found that tire wear particles can also harbor toxic organic chemicals that threaten aquatic environments.

But it isn’t just our rivers and ponds that are at risk – research has shown that microplastics can also be transported long distances via air currents.

Recent models constructed by researchers at Cornell Univeristy suggest that flat microplastic fibers are carried the furthest by these air streams. These flat fibers also appear to be spending 450% more time in the lower atmosphere than previously calculated. Improved models, like this new Cornell model, will help scientists to better determine the sources of airborne microplastic pollution, the researchers say.

“We can now more accurately attribute the sources of microplastic particles that will eventually come to be transported to the air,” said Qi Li, an assistant professor in the Department of Civil and Environmental Engineering at Cornell University and the senior author of the paper. “If you know where they’re coming from, then you can come up with a better management plan and policies or regulations to reduce the plastic waste.”

The damage done by microplastic

Dietary sources of microplastic are also of special interest to environmental researchers.

Bottled water is a significant source of dietary microplastic, with one recent study suggesting that 1 liter of bottled water contains on average around 240,000 detectable plastic fragments.

If you are a tea drinker, you might also be exposed to microplastics originating from polyethylene terephthalate (PET) or nylon-based teabags. According to one 2019 study, a single plastic teabag can release up to  11.6 billion microplastics and 3.1 billion nanoplastics into a single cup of tea. Another study published in 2021 also suggests that this kind of microplastic particle release from teabags might be enhanced if the teabag is microwaved.

Regardless of its source, once this microplastic has entered your body, researchers want to know if it poses any risks.

According to a new paper in Environmental Health Perspectives, microplastics in the gut and digestive tract are capable of migrating around the body, making their way into kidney, liver and brain tissues.

The research, led by Dr. Eliseo Castillo, an associate professor of gastroenterology and hepatology at the University of New Mexico School of Medicine, exposed mice to microplastic-contaminated drinking water for four weeks.

“Over the past few decades, microplastics have been found in the ocean, in animals and plants, in tap water and bottled water. They appear to be everywhere,” Castillo said.

They found that the microplastics easily crossed the mice’s intestinal barrier, infiltrating other tissues. The study also showed some evidence that the presence of microplastics could change metabolic pathways within the affected tissues.

“These mice were exposed for four weeks,” Castillo said. “Now, think about how that equates to humans, if we're exposed from birth to old age.”

Towards a plastic-free world

In the face of widespread microplastic contamination and continued research into associated health effects, other research groups are hard at work investigating new ways to clean up this contamination.

Researchers from the University of Waterloo have developed a new technology that uses activated carbon derived from thermoset epoxy resin to remove nanoplastics from water. According to the researchers, the method is 94% efficient and could also help to give epoxy – a polymer that is normally not reusable or reprocessable – a second life.

“To end the plastic waste crisis and reduce the environmental impact of plastics production, we need to implement a circular economy approach that considers every stage of the plastic journey,” said study author Tizazu Mekonnen, a professor of engineering at the University of Waterloo.

Others are looking at whether hydrogel materials could be the answer. In a 2024 paper published in Nanoscale, researchers from the Indian Institute of Science demonstrated a multi-layered hydrogel that can remove microplastics from water via adsorption, before breaking them down further upon exposure to UV light. This enables their hydrogel to be reused up to five times before it is also upcycled to form useful carbon nanomaterials.

Beyond microplastics remediation, many also believe that it is important to develop more sustainable alternatives to traditional plastic. Researchers from the University of California San Diego and materials science company Algenesis recently reported in Scientific Reports the creation of a bio-based thermoplastic polyurethane that fully biodegrades in less than seven months, even at the microplastic level.

“We're just starting to understand the implications of microplastics. We've only scratched the surface of knowing the environmental and health impacts,” said study author Michael Burkart, a professor of chemistry and biochemistry at the University of California San Diego. “We're trying to find replacements for materials that already exist, and make sure these replacements will biodegrade at the end of their useful life instead of collecting in the environment. That's not easy.”