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Managing Microplastics Taking a magnifying glass to this tiny threat
A macroscopic view of microplastic formation Microplastics are everywhere, from the tallest mountains to the deepest depths of the ocean. Where do they come from, and how did they end up there?
Should we be worried about the microplastics in our bodies? How these tiny particles may harm our health is unclear, but scientists are alarmed by what they are finding so far
Can biodegradable polymers make microplastics? Yes, and how long they last depends on where they end up
Enzymes to make plastics disappear Scientists are giving nature a nudge and coaxing enzymes to break down plastics
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A macroscopic view of microplastic formation
Microplastics are everywhere, from the tallest mountains to the deepest depths of the ocean. Where do they come from, and how did they end up there?
by Fionna Samuels, C&EN staff
November 25, 2024 | Appeared In Volume 102, Issue 37
Twenty years ago, Richard Thompson, a marine biologist at the University of Plymouth, and his colleagues first used the term microplastic to describe the microscopic bits of plastic they were finding and trying to quantify in marine sediments around Plymouth, England. Four years later, participants of an international workshop hosted by the US National Oceanic and Atmospheric Administration defined microplastics as “plastic particles smaller than 5 mm.” Policy makers started using the term shortly thereafter.
Since then, scientists have embraced this definition and published hundreds of papers on the environmental accumulation of microplastics and their possible sources. “We use so much plastic in our daily life, and it breaks down and sloughs off over time,” ecologist Chelsea Rochman of the University of Toronto says. “So microplastics, truly at this point, are everywhere.” The most prevalent source of plastic, however, will vary from place to place. With proper monitoring, she adds, people “can start to mitigate based on those sources.”
Minimizing plastic consumption and managing waste properly could help decrease microplastic pollution, says Denise Mitrano, an environmental analytical chemist at the Swiss Federal Institute of Technology (ETH), Zurich. “Plastics still are useful and needed in our modern society,” she says, but “we need to find a better, sustainable way to use them.”
The onus to find and implement solutions falls on all of us—individuals, policymakers, and industry leaders, Thompson says. “We know an awful lot more now than we did 20 years ago about the pervasive nature, the accumulation, the distribution, and the impacts” of microplastics, he says. Thompson and his colleagues collated such information in a recent review (Science 2024, DOI: 10.1126/science.adl2746). “To me, what all that is pointing towards is that we need to move towards solutions.”
1
Textiles
From fuzzy fleeces to slick, sweat-wicking sportswear, synthetic textiles are staples in most wardrobes. Unfortunately, such fabrics are a leading contributor of microplastics in the environment, shedding tiny strands of polyester, polyamide, acrylic, and other polymers. “It’s coming off as we walk but also when we wash and when we dry” and during manufacturing, Rochman says.
Consumers can buy specialized filters or washing bags to minimize the amount of microfiber waste released from their laundry. But Thompson argues that fabric manufacturers can do more. Recent research shows that textile characteristics such as composition, yarn structure, fabric construction, and postproduction treatments can all affect fiber shedding (Text. Res. J. 2024, DOI: 10.1177/00405175241260066). Intentionally designing better textiles could reduce shedding, Thompson says.
2
Paints
A new coat of paint can change a building’s style, protect a ship from rusting, or reroute traffic through an intersection. But polymers are a key ingredient in paints. Rochman says that “when we paint houses and boats and roads, that paint cracks and chips over time,” flaking into microplastics that escape into the surrounding ecosystems. Leakage can also occur when old paint is removed and a new coat is applied. All together, these pathways and the prevalence of paint make paint one of the largest sources of microplastics in the environment, Rochman says.
3
Tires
Every driver knows that tires wear down over time, going bald and becoming brittle with age. It is perhaps unsurprising, then, that tires are a leading source of microplastic pollution. Tires today are made of both natural and synthetic rubber. As a person drives, friction shreds off micrometer-size bits of tire, sending the pieces into the air and dirt.
Although removing tires from daily life is unfeasible, Thompson suggests that the industry can do more than simply maintain the status quo. Researchers have already established that some tire designs currently in use shed less microplastic than others. Those designs were unintentional, he says, “so there’s lots of opportunity for innovation.”
4
Macroplastics
Physical perturbations, exposure to ultraviolet light, and oxidation will ultimately break down macroplastics into microplastics. This is the fate of many plastic products that are released purposefully, like agricultural fabric, or accidentally, like mismanaged trash or lost fishing nets. The rate of degradation from macroplastic into microplastic, however, will depend on the polymer species and the environment it lands in, Thompson says.
5
Nurdles and cosmetics
Some microplastics are released directly into the environment. Nurdles, the small plastic pellets used as the raw material for many consumer goods, spill into the environment at every step along their supply chain. The largest known plastic spill to date occurred in 2021 in Sri Lanka when a ship caught fire and partially sank, spilling 1,680 metric tons of nurdles into the water. These killed numerous marine animals who mistook the pellets for a tasty snack. Although international regulations of nurdles have been proposed, none have yet been agreed upon.
By contrast, over 30 countries have banned the addition of plastic microbeads to personal care products—often exfoliants such as toothpaste and facial cleanser. It was a success, Thompson says, that governments acted relatively quickly once environmental scientists made it clear the beads were escaping water treatment plants. But, he argues, the first patents for microbeads in cosmetics were filed nearly 50 years before the regulations were in place. “Did nobody in the industry ever wonder, ‘Where are those hundreds of thousands of tons of plastic that we put into cosmetics going every year?’ ” he asks.
6
Soil
Once released, microplastics cycle through the environment, often ending up buried in soil. But the type of microplastic particle that researchers find in the soil depends on the location, Mitrano says. In city centers and along roadsides, particles from tires likely dominate, Mitrano says. In farmlands, microplastics can come from the direct use of plastics—for example, mulching films—or from soil amendments—for example, sewage sludge. However, not all countries allow the use of soil sludge, she adds.
To understand the broader impact of microplastics in soil, Mitrano’s group is working to understand how various types of microplastics, each with their own morphologies and chemical compositions, change soil structure. Such changes could affect the aeration rate, water flow, and nutrient transport through soil, she says.
7
Water
Precipitation can wash microplastic pollution out of the air and off the land, sending the debris into waterways that will ultimately feed it into the ocean. Understanding microplastics’ aquatic journey is an ongoing area of research.
Rochman is leading an ecosystem-wide experiment at the Experimental Lakes Area in Canada, where “we’re actually adding microplastics to a lake,” she says. Her team has found that microplastics are pseudopersistent in the water column between surface and sediment. Surface tension keeps tiny pieces of plastic at the surface for some time, she says, but “once it’s in the water column, it starts to sink.” The size, shape, and composition of a plastic determine how long it takes to sink, but all the pieces ultimately end up buried in the bottom sediment.
Why, then, is microplastic pollution still a problem in the water column? Because of the continuous flow of plastics into the environment, Rochman says. “If we turn off the tap, the microplastic wouldn’t be in the water column anymore.”
8
Air
Some microplastic particles are light enough to be lofted into the atmosphere. They have been found in the air above urban and rural areas, as well as over remote corners of the earth, such as the open ocean. Plastic particles can travel from cities in a dusty breeze, be spat into the air by breaking waves in contaminated waterways, and be eroded from soil by gusts of wind. Once in the air, microplastics can travel thousands of kilometers from their original source before settling onto the ground or into the water (Nat. Geosci. 2022, DOI: 10.1038/s41561-022-01051-9).
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Chemical & Engineering News
ISSN 0009-2347
Copyright © 2024 American Chemical Society
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Pollution
A macroscopic view of microplastic formation
Microplastics are everywhere, from the tallest mountains to the deepest depths of the ocean. Where do they come from, and how did they end up there?
by Fionna Samuels
November 25, 2024
| A version of this story appeared in
Volume 102, Issue 37
Credit: Yang H. Ku/C&EN/Shutterstock
COVER STORY
A macroscopic view of microplastic formation
Twenty years ago, Richard Thompson, a marine biologist at the University of Plymouth, and his colleagues first used the term microplastic to describe the microscopic bits of plastic they were finding and trying to quantify in marine sediments around Plymouth, England. Four years later, participants of an international workshop hosted by the US National Oceanic and Atmospheric Administration defined microplastics as “plastic particles smaller than 5 mm.” Policy makers started using the term shortly thereafter.
Since then, scientists have embraced this definition and published hundreds of papers on the environmental accumulation of microplastics and their possible sources. “We use so much plastic in our daily life, and it breaks down and sloughs off over time,” ecologist Chelsea Rochman of the University of Toronto says. “So microplastics, truly at this point, are everywhere.” The most prevalent source of plastic, however, will vary from place to place. With proper monitoring, she adds, people “can start to mitigate based on those sources.”
Minimizing plastic consumption and managing waste properly could help decrease microplastic pollution, says Denise Mitrano, an environmental analytical chemist at the Swiss Federal Institute of Technology (ETH), Zurich. “Plastics still are useful and needed in our modern society,” she says, but “we need to find a better, sustainable way to use them.”
The onus to find and implement solutions falls on all of us—individuals, policymakers, and industry leaders, Thompson says. “We know an awful lot more now than we did 20 years ago about the pervasive nature, the accumulation, the distribution, and the impacts” of microplastics, he says. Thompson and his colleagues collated such information in a recent review (Science 2024, DOI: 10.1126/science.adl2746). “To me, what all that is pointing towards is that we need to move towards solutions.”
1. Textiles
From fuzzy fleeces to slick, sweat-wicking sportswear, synthetic textiles are staples in most wardrobes. Unfortunately, such fabrics are a leading contributor of microplastics in the environment, shedding tiny strands of polyester, polyamide, acrylic, and other polymers. “It’s coming off as we walk but also when we wash and when we dry” and during manufacturing, Rochman says.
Consumers can buy specialized filters or washing bags to minimize the amount of microfiber waste released from their laundry. But Thompson argues that fabric manufacturers can do more. Recent research shows that textile characteristics such as composition, yarn structure, fabric construction, and postproduction treatments can all affect fiber shedding (Text. Res. J. 2024, DOI: 10.1177/00405175241260066). Intentionally designing better textiles could reduce shedding, Thompson says.
2. Paints
A new coat of paint can change a building’s style, protect a ship from rusting, or reroute traffic through an intersection. But polymers are a key ingredient in paints. Rochman says that “when we paint houses and boats and roads, that paint cracks and chips over time,” flaking into microplastics that escape into the surrounding ecosystems. Leakage can also occur when old paint is removed and a new coat is applied. All together, these pathways and the prevalence of paint make paint one of the largest sources of microplastics in the environment, Rochman says.
3. Tires
Every driver knows that tires wear down over time, going bald and becoming brittle with age. It is perhaps unsurprising, then, that tires are a leading source of microplastic pollution. Tires today are made of both natural and synthetic rubber. As a person drives, friction shreds off micrometer-size bits of tire, sending the pieces into the air and dirt.
Although removing tires from daily life is unfeasible, Thompson suggests that the industry can do more than simply maintain the status quo. Researchers have already established that some tire designs currently in use shed less microplastic than others. Those designs were unintentional, he says, “so there’s lots of opportunity for innovation.”
4. Macroplastics
Physical perturbations, exposure to ultraviolet light, and oxidation will ultimately break down macroplastics into microplastics. This is the fate of many plastic products that are released purposefully, like agricultural fabric, or accidentally, like mismanaged trash or lost fishing nets. The rate of degradation from macroplastic into microplastic, however, will depend on the polymer species and the environment it lands in, Thompson says.
5. Nurdles and cosmetics
Some microplastics are released directly into the environment. Nurdles, the small plastic pellets used as the raw material for many consumer goods, spill into the environment at every step along their supply chain. The largest known plastic spill to date occurred in 2021 in Sri Lanka when a ship caught fire and partially sank, spilling 1,680 metric tons of nurdles into the water. These killed numerous marine animals who mistook the pellets for a tasty snack. Although international regulations of nurdles have been proposed, none have yet been agreed upon.
By contrast, over 30 countries have banned the addition of plastic microbeads to personal care products—often exfoliants such as toothpaste and facial cleanser. It was a success, Thompson says, that governments acted relatively quickly once environmental scientists made it clear the beads were escaping water treatment plants. But, he argues, the first patents for microbeads in cosmetics were filed nearly 50 years before the regulations were in place. “Did nobody in the industry ever wonder, ‘Where are those hundreds of thousands of tons of plastic that we put into cosmetics going every year?’ ” he asks..
6. Soils
Once released, microplastics cycle through the environment, often ending up buried in soil. But the type of microplastic particle that researchers find in the soil depends on the location, Mitrano says. In city centers and along roadsides, particles from tires likely dominate, Mitrano says. In farmlands, microplastics can come from the direct use of plastics—for example, mulching films—or from soil amendments—for example, sewage sludge. However, not all countries allow the use of soil sludge, she adds.
To understand the broader impact of microplastics in soil, Mitrano’s group is working to understand how various types of microplastics, each with their own morphologies and chemical compositions, change soil structure. Such changes could affect the aeration rate, water flow, and nutrient transport through soil, she says.
7. Water
Precipitation can wash microplastic pollution out of the air and off the land, sending the debris into waterways that will ultimately feed it into the ocean. Understanding microplastics’ aquatic journey is an ongoing area of research.
Rochman is leading an ecosystem-wide experiment at the Experimental Lakes Area in Canada, where “we’re actually adding microplastics to a lake,” she says. Her team has found that microplastics are pseudopersistent in the water column between surface and sediment. Surface tension keeps tiny pieces of plastic at the surface for some time, she says, but “once it’s in the water column, it starts to sink.” The size, shape, and composition of a plastic determine how long it takes to sink, but all the pieces ultimately end up buried in the bottom sediment.
Why, then, is microplastic pollution still a problem in the water column? Because of the continuous flow of plastics into the environment, Rochman says. “If we turn off the tap, the microplastic wouldn’t be in the water column anymore.”
8. Air
Some microplastic particles are light enough to be lofted into the atmosphere. They have been found in the air above urban and rural areas, as well as over remote corners of the earth, such as the open ocean. Plastic particles can travel from cities in a dusty breeze, be spat into the air by breaking waves in contaminated waterways, and be eroded from soil by gusts of wind. Once in the air, microplastics can travel thousands of kilometers from their original source before settling onto the ground or into the water (Nat. Geosci. 2022, DOI: 10.1038/s41561-022-01051-9).
Chemical & Engineering News
ISSN 0009-2347
Copyright © 2024 American Chemical Society
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