How microplastics are making their way into our farmland

by Branaavan Sivarajah and Jesse Vermaire, The Conversation

In Canada and around the world, biosolids are widely used to improve agricultural farmland

 soil. Biosolids being sprayed on an agricultural field. 

Credit: Branaavan Sivarajah, Author provided

Microplastic pollution is a global environmental problem that is ubiquitous in all environments, including air, water and soils.

Microplastics are readily found in treated wastewater sludge—also known as municipal biosolids—that eventually make their way to our agricultural soils.

Our recent investigation of microplastic levels in Canadian municipal biosolids found that a single gram of biosolids contains hundreds of microplastic particles. This is a much greater concentration of microplastics than is typically found in air, water or soil.

Given that hundreds of thousands of tons of biosolids are produced every year in Canada, we need to pay close attention to the potential impacts such high levels of microplastics might have on the environment and find ways to reduce microplastic levels in Canada's wastewater stream.

Municipal biosolids

Municipal biosolids are produced at wastewater treatment plants by settling and stabilizing the solid fraction of the municipal wastewater inflow.

In Canada and around the world, municipal biosolids are used to improve agricultural farmland soil. This is because they are rich in nutrients needed for plant growth, such as phosphorus and nitrogen.

Biosolids applied to an agricultural field. Credit: Branaavan Sivarajah, Author provided

Municipal biosolid applications are carefully regulated in Canada for heavy metals, nutrients and pathogens. However, guidelines for emerging contaminants, such as microplastics, are not currently available.

While current wastewater treatment plants are not explicitly designed to remove microplastics, they are nevertheless efficient at removing nearly 90 percent of microplastic contaminants. The removed microplastics are often concentrated in the settled sludge and eventually end up in the biosolids.

Microplastics in municipal biosolids

Previous studies have shown that municipal biosolid waste is an important pathway for microplastics to enter the broader terrestrial ecosystems, including agricultural fields.

In collaboration with scientists from Environment and Climate Change Canada and Agriculture and Agri-Food Canada, we conducted the first pan-Canadian assessment of microplastics in municipal biosolids. We analyzed biosolid samples from 22 Canadian wastewater treatment plants across nine provinces and two biosolid-based fertilizer products.

We found hundreds of microplastic particles in every gram of biosolids. The most common type of microplastic particles we observed were microfibres, followed by small fragments. We found small amounts of glitter and foam pieces too.

Microplastic concentrations in municipal biosolids are substantially higher than other environmental networks in Canada like water, soil and river sediments. This provides further evidence that microplastics are concentrated in biosolids produced at wastewater treatment plants.

Microplastics in municipal biosolids. A-C: Processed biosolid samples; D-F: Assortment of microplastic particles in biosolids. Credit: Jesse Vermaire, Author provided

Reducing microplastics

Wastewater treatment plants are well-equipped to remove large plastics like bottle caps and plastic bags from municipal wastewater. However, microplastic particles are so small they can't be caught by current treatment infrastructure, so they end up concentrating in wastewater sludge.

As wastewater streams concentrate microplastics, they also offer an opportunity to reduce the plastic pollution that is entering the environment. While researchers across Canada are working to find insights on the short- and long-term ecological consequences of microplastic pollution on soil ecosystems, one solution is already clear.

Microplastics can be reduced at sources via systematic reductions in the use of single-use plastics, washing clothing with synthetic fiber less frequently and removing microfibres using washing machine filters. These approaches will help minimize the amount of microplastics that get into the wastewater stream and, ultimately, into the broader terrestrial and aquatic environments.

Building new technologies at our wastewater treatment plants to remove microplastics through physical or chemical means should also be explored.

We need to better understand the impact of high concentrations of microplastic on agro-ecosystems where biosolids are applied, including its impacts on soil-dwelling organisms like earthworms and insects. We also need to start building national guidelines for microplastic levels in biosolids and agricultural soils.

More information: Branaavan Sivarajah et al, How many microplastic particles are present in Canadian biosolids?, Journal of Environmental Quality (2023). DOI: 10.1002/jeq2.20497

Journal information: Journal of Environmental Quality 

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Scientists study how a diabetes drug affects soils

Microplastic pollution: New device uses wood dust to trap up to 99.9% of microplastics in water

by University of British Columbia

Different types of wood waste can be used to create the water filter. 

Credit: UBC Forestry/Jillian van der Geest

Could plants be the answer to the looming threat of microplastic pollution? Scientists at UBC's BioProducts Institute found that if you add tannins—natural plant compounds that make your mouth pucker if you bite into an unripe fruit—to a layer of wood dust, you can create a filter that traps virtually all microplastic particles present in water.

While the experiment remains a lab set-up at this stage, the team is convinced that the solution can be scaled up easily and inexpensively once they find the right industry partner.

Microplastics are tiny pieces of plastic debris resulting from the breakdown of consumer products and industrial waste. Keeping them out of water supplies is a huge challenge, says Dr. Orlando Rojas, the institute's scientific director and the Canada Excellence Research Chair in Forest Bioproducts.

He noted one study which found that virtually all tap water is contaminated by microplastics, and other research which states that more than 10 billion tons of mismanaged plastic waste will be dispersed in the environment by 2025.

"Most solutions proposed so far are costly or difficult to scale up. We're proposing a solution that could potentially be scaled down for home use or scaled up for municipal treatment systems. Our filter, unlike plastic filters, does not contribute to further pollution as it uses renewable and biodegradable materials: tannic acids from plants, bark, wood and leaves, and wood sawdust—a forestry byproduct that is both widely available and renewable."

Captures a wide variety of plastics

For their study, the team analyzed microparticles released from popular tea bags made of polypropylene. They found that their method (they're calling it "bioCap") trapped from 95.2 percent to as much as 99.9 percent of plastic particles in a column of water, depending on plastic type. When tested in mouse models, the process was proved to prevent the accumulation of microplastics in the organs.

Dr. Rojas, a professor in the departments of wood science, chemical and biological engineering, and chemistry at UBC, adds that it's difficult to capture all the different kinds of microplastics in a solution, as they come in different sizes, shapes and electrical charges.

"There are microfibers from clothing, microbeads from cleansers and soaps, and foams and pellets from utensils, containers and packaging. By taking advantage of the different molecular interactions around tannic acids, our bioCap solution was able to remove virtually all of these different microplastic types."

Collaborating on sustainable solutions

The UBC method was developed in collaboration with Dr. Junling Guo, a professor at the Center of Biomass Materials and Nanointerfaces at Sichuan University in China. Marina Mehling, a Ph.D. student at UBC's department of chemical and biological engineering, and Dr. Tianyu Guo, a postdoctoral researcher at the BioProducts Institute, also contributed to the work.

"Microplastics pose a growing threat to aquatic ecosystems and human health, demanding innovative solutions. We're thrilled that the BioProducts Institute's multidisciplinary collaboration has brought us closer to a sustainable approach to combat the challenges posed by these plastic particles," said Dr. Rojas.

More information: Yu Wang et al, Flowthrough Capture of Microplastics through Polyphenol‐Mediated Interfacial Interactions on Wood Sawdust, Advanced Materials (2023). DOI: 10.1002/adma.202301531

Journal information: Advanced Materials 

Provided by University of British Columbia

How microplastics are making their way into our farmland

 

Study maps human uptake of microplastics across 109 countries

by Syl Kacapyr, Cornell University

Dietary and airborne MP uptake pathway overview and uptake reduction by water quality

 control aided by aquatic plastic debris removal in 109 major developing and industrialized

 countries.

 Credit: Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c00010

Southeast Asian countries such as Indonesia, Malaysia and the Philippines top the global per capita list of dietary uptakes of microplastics, while China, Mongolia and the United Kingdom top the list of countries that breathe the most microplastics, according to a new study by Cornell researchers mapping microplastic uptake across 109 countries.

The study, published April 24 in the journal Environmental Science & Technology, builds on existing data models estimating how much microplastic humans unwittingly eat and inhale as a result of untreated plastic debris degrading and dispersing into the environment.

To more comprehensively estimate human consumption, the Cornell study accounts for each country's eating habits, food processing technologies, age demographics and breathing rates—all factors that contribute to differences in how residents of each country consume microplastics.

"The uptake of microplastics at the country level is a critical indicator of plastic pollution and public health risks," said Fengqi You, the Roxanne E. and Michael J. Zak Professor in Energy Systems Engineering, who co-authored the study with doctoral student Xiang Zhao. "Comprehensive global mapping supports local pollution mitigation efforts through enhanced water quality control and effective waste recycling."

The study assesses dietary uptake by compiling data on microplastic concentrations in subcategories of major food groups such as fruits, vegetables, proteins, grains, dairy, drinks, sugars, salt and spices. The models also use data detailing how much of those foods are consumed in different countries. For instance, table salt consumption, per capita, is about equal in Indonesia and the U.S., but the microplastic concentration in Indonesian table salt is around 100 times higher.

Overall, the study found that Indonesians eat about 15 grams of microplastics per month—more than any other country—with the majority of plastic particles coming from aquatic sources such as seafood. That is a 59-fold increase in daily microplastic consumption from 1990 to 2018, the date range used for the models. U.S. dietary intake of microplastics is estimated to be about 2.4 grams per month, while the lowest is Paraguay at 0.85 grams.

Per capita daily MP dietary and inhalation uptake rates at the country level in 109

 industrialized and developing countries within Asia, Europe, Africa, and North and 

South America, focusing on the world’s major coastlines that are affected by plastic 

pollution. 

Credit: Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c00010

Data on airborne microplastic concentration, age demographics and human respiration rates were used to calculate microplastics being inhaled. Residents of China and Mongolia topped the list, breathing in more than 2.8 million particles per month. U.S. residents inhale about 300,000 particles per month. Only residents in the Mediterranean and nearby regions breathed less, with countries like Spain, Portugal and Hungary breathing about 60,000 to 240,000 particles per month.

"Industrialization in developing economies, particularly in East and South Asia, has led to increased consumption of plastic materials, waste generation and human microplastic uptake. Conversely, industrialized countries are experiencing a reverse trend, supported by greater economic resources to reduce and remove free plastic debris," said You, who is a senior faculty fellow at the Cornell Atkinson Center for Sustainability.

You added that the study can inform reduction strategies for microplastic uptake that are tailored to local economies and industrial contexts, but that such efforts require international collaboration, such as technology support from developed countries to advance waste reduction strategies.

According to the study, a 90% reduction in aquatic plastic debris could lead to substantial decreases in microplastic exposure, potentially by up to 51% in developed countries and 49% in highly industrializing regions.

The study was published on the heels of an April 23–29 meeting of an international committee negotiating the U.N. Plastics Treaty, a legally binding agreement that would establish global rules around plastic production and disposal. The agreement is expected to be finalized later this year, with a focus on international collaboration to reduce microplastics in marine environments.

"Cleaning the global surface water system is a marathon influenced by local industrial and socioeconomic settings," Zhao said. "However, our global map that pinpoints aquatic microplastic hotspots can initiate this journey, and our study highlights that addressing microplastic uptake requires a multifaceted approach, including sustainable packaging solutions, enforcing stringent waste management regulations and advancing water treatment technologies."

More information: Xiang Zhao et al, Microplastic Human Dietary Uptake from 1990 to 2018 Grew across 109 Major Developing and Industrialized Countries but Can Be Halved by Plastic Debris Removal, Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c00010

Journal information: Environmental Science & Technology 

Provided by Cornell University Every breath you take: Following the journey of inhaled plastic particle pollution

 

Microplastics in soil: Tomography with neutrons and X-rays shows where particles are deposited

Peer-Reviewed Publication

HELMHOLTZ-ZENTRUM BERLIN FÜR MATERIALIEN UND ENERGIE

 

IMAGE: 

A SAMPLE OF BEELITZ SANDY SOIL CONTAINING FRAGMENTS OF THIN POLYETHYLENE FILM (PET) WAS ANALYSED HERE. SUCH FILMS ARE USED IN ASPARAGUS CULTIVATION. THE NEUTRON TOMOGRAPHY (IN SHADES OF GREY) SHOWS WHERE THE PET FRAGMENTS ARE LOCATED. X-RAY TOMOGRAPHY OF THE SAMPLE (OCHRE) REVEALS THE SOIL STRUCTURE: SUPERIMPOSED ON THE NEUTRON TOMOGRAPHY, THE PET PARTICLES (IN BLUE) CONTAINED THEREIN BECOME VISIBLE.

view more 

CREDIT: C. TÖTZKE / HZB / UNI POTSDAM

It is a real problem: Microplastic particles are everywhere. Now a team from the University of Potsdam and HZB has developed a method that allows it for the first time to precisely localise microplastic particles in the soil. The 3D tomographies show where the particles are deposited and how structures in the soil are changed. The method was validated on prepared samples. The team used a special instrument at the neutron source of the Institut Laue-Langevin in Grenoble to carry out neutron and X-ray analyses simultaneously. 

Microplastic particles are a major environmental pollutant today. Road traffic accounts for a particularly large proportion: in Germany alone, tyre wear is said to generate around one hundred thousand tonnes of microplastics every year, in addition to particles from astroturf, cosmetics, washing powders, clothing, disposable masks, plastic bags and other waste that end up in nature. Microplastic particles can now be found everywhere. But what happens to these particles in different soils? Do they break up into smaller and smaller pieces and how are they relocated and transported, changing the structures in the soil?

Some of these questions are already being analysed: A soil sample is floated in a heavy salt solution, whereupon the individual components separate according to density: Plastic and organic particles float to the top, while mineral particles sink. The mixture of organic material and plastic particles is then treated with hydrogen peroxide, for example, whereby the organic components decompose and the microplastic particles should remain. Although this method makes it possible to determine the quantity and type of microplastic in a soil sample, information is lost as to where exactly these particles accumulate in the soil and whether they change any structures in the soil. 

3D tomography with neutrons and X-rays

In their new study, Prof Sascha Oswald (University of Potsdam) and Dr Christian Tötzke (University of Potsdam and HZB) have now presented a method to answer these questions. They worked closely with the team led by Dr Nikolay Kardjilov, HZB, whose expertise went into setting up a unique instrument at the Institut Laue-Langevin, Grenoble: there, samples can be analysed with neutrons and X-rays to create 3D tomographies simultaneously, i.e. without altering the sample. While neutrons visualise organic and synthetic particles, X-ray tomography shows the mineral particles and the structure they form.

Method tested on prepared soil samples

To test the method, Tötzke prepared a series of soil samples from sand, organic components such as peat or charcoal and artificial microplastic particles. In a further series of measurements, he investigated how the roots of fast-growing lupins penetrate the soil samples and how they react to the presence of microplastics.

In the neutron tomograms, the microplastic particles are clearly identified, as can some of the organic components. X-ray tomography, on the other hand, provides an insight into the arrangement of the sand grains, whereas the organic and plastic particles are shown as diffuse voids. When superimposed, a complete image of the soil sample is obtained. This allows the scientists to estimate the size and shape of the microplastic particles, as well as the changes to the soil structure caused by the embedded microplastics. 

"This method is quite complex, but it makes it possible for the first time to investigate where microplastic particles are deposited and how they change the soil and its structure," explains Tötzke. He also analysed sandy soil from a field near Beelitz, a typical asparagus-growing area in Brandenburg near Berlin, into which he mixed pieces of so called mulch film, a very thin plastic film used to protect the plants. In “real life” farming it is usually not possible to remove this film after use completely. Remaining film residues are then carried into deeper soil layers during ploughing "We were able to show that fragments of such films can change the water flow in the soil. Microplastic fibres, on the other hand, created small cracks in the soil matrix," says Tötzke. It is not yet possible to predict how this will affect the soil’s hydraulic properties, for example its ability to store water. "As droughts and heavy rainfall become more likely with climate change, it is urgent to answer these questions. We now need to investigate this systematically," says Tötzke.

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JOURNAL

Science of The Total Environment

DOI

10.1016/j.scitotenv.2023.167927 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Non-invasive 3D analysis of microplastic particles in sandy soil — Exploring feasible options and capabilities

ARTICLE PUBLICATION DATE

9-Nov-2023

ECO-CSI

Crime scene tape set to revolutionize microplastics research

Forensic scientists have developed a new method to help monitor plastic pollution across the world.

STAFFORDSHIRE UNIVERSITY

Research News

IMAGE: EASYLIFT® TAPE BEING USED ONBOARD THE AMERICAN PROMISE DURING THE HUDSON RIVER EXPEDITION view more 

CREDIT: STAFFORDSHIRE UNIVERSITY

An adhesive tape patented by Staffordshire University researchers to recover trace evidence from crimes scenes is being adopted to analyse microplastics more efficiently.

Man-made polymer particles or ‘microplastics’ are proven to be present in land, air and water environments. However, despite extensive global studies, there is no standardised approach for their collection and analysis.

Currently, studies regularly involve retrieving microplastic samples from water using a filtration method. Samples are commonly analysed in situ on the filter or after removal from it by hand, which is time consuming and risks accidental loss of the particles and cross contamination.

Claire Gwinnett, Professor of Forensic and Environmental Science, is part of the team that created Easylift® tape more than a decade ago and has more recently applied her expertise in fibre analysis to microplastics.

She explained: “Easylift® tape was developed for the forensic market. However, what we have found is that the same benefits are true when looking at particulates from any environment.

“We realised that it holds great potential for microplastics work particularly when you are out in the field, for example on a boat or on a beach, where the risk of losing or contaminating your microplastic samples is huge.”

A new paper, published in Environmental Advances, addresses the shortcomings of current research methods and sets out a new workflow using Easylift® tape. The technique uses the self-adhesive tape to ‘lift’ microplastic particles from a filter then safely preserves them between the tape and a sheet of suitable material – in this case glass.

This method was trialled by Professor Gwinnett during an expedition to collect microplastic samples along the Hudson River in New York with the Rozalia Project where it proved highly effective, with a mean fibre recovery rate of 96.4%. It also enables multiple analytical techniques to be applied to the samples afterwards and preserves them for future study.

Professor Gwinnett said: “The ultimate goal is that this will become the standardised workflow for microplastics research across the world. At the moment, scientists are extrapolating data and it is only through constant monitoring that we will we truly know how much microplastic pollution is out there. If there is a standardised method to globally track microplastics then we can much better understand the risks and where we should be targeting our efforts for mitigation.

“We know plastic pollution is widespread, but we need to understand how much is in different locations, where it has come from and where it is going. What we need is a global collaborative effort to gather that large-scale data.”

CAPTION

Professor Claire Gwinnett collecting microplastic samples from the Hudson River in New York

CREDIT

Annie Tuthill

Easylift® tape is already being employed more widely and was used to collect microplastic samples during a transatlantic sailing expedition on former racing vessel the SV Jolokia last year. The Marine Education Centre based in New York State is also training ‘citizen scientists’ to take samples from the Hudson River and other locations using the tape.

Staffordshire University is now collaborating with the University of Oxford and Nekton Mission to analyse microplastic samples from an expedition to the Antarctic where these particulates will be retrieved from ice cores using Easylift® tape.

Professor Gwinnett added: “We need the ability for people to constantly monitor plastic pollution without massive expertise and the beauty of Easylift® is that it can be used by anyone – volunteers, sailing crews, people working in waste-water management can all use this in a robust way.

“It will allow us to share microplastic samples with partner institutions across the world for further analysis and to validate research methods. As with evidence recovered from crime scenes, we will also be able to store microplastic samples to be re-examined in a decade’s time or longer. Being able to collaborate and share research in this way is an exciting step forward.”

Read the full paper The application of tape lifting for microplastic pollution monitoring in Environmental Advances.

 

Citizen scientists help discover microplastics along the entire German coastline

The AWI's citizen science project "Microplastic Detectives" has analyzed 2.2 tons of sand from German coasts for microplastics

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

 

image: 

An empty plastic bottle lies on the beach. Washed up on Sylt's west beach after a stormy night.

view more 

Credit: Alfred Wegener Institute / Sina Löschke

The global production of plastics and the resulting plastic waste has increased to such an extent that plastics have become ubiquitous in our environment. Plastics of various sizes are also found along the German North Sea and Baltic coasts. Previous studies of microplastic pollution on German beaches have often been limited to a few locations. In the citizen science project “Microplastic Detectives”, researchers from the Alfred Wegener Institute, together with citizens, have now collected samples from beaches along the entire German coast to be analyzed for microplastics. The resulting dataset is the first to be large enough to make reliable estimates of the state of pollution along the entire German coastline. The team is publishing its findings in the journal Frontiers in Environmental Science.

Global plastics production could almost triple by 2060, according to estimates by the Organisation for Economic Co-operation and Development (OECD). This leads to more plastic waste and a build-up of plastic in water bodies, where it breaks down into microplastics - particles smaller than or equal to five millimeters. “This irreversible plastic pollution is affecting species, populations and ecosystems, including along the German coast,” says Dr Bruno Walther, formerly of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), now at Heinrich Heine University Düsseldorf and lead author of the recently published study. The extent to which our beaches in the North Sea and Baltic Sea are polluted has so far only been assessed for individual areas or locations, but not for the entire German coast. “This is why we launched the citizen research project 'Microplastic Detectives' to collect comparable data on the large-scale distribution of microplastic pollution along the German coastline.”

With the help of citizen scientists, the research team was able to collect a total of 2.2 tons of sand from 71 locations along the German coast, covering a total area of 68.36 square meters. “We have combined a total of 1139 comparable samples into one large dataset. That's more geographic coverage than we’ve ever had before,” says co-author and AWI biologist Dr Melanie Bergmann. The samples were then dried at the AWI, sieved and analyzed under a microscope for plastic particles as small as one millimeter in size. “In this study, we deliberately focused on large microplastics in order to rule out airborne contamination with small microplastic particles and to simplify sampling for the citizen scientists.”

The results were surprising: “Although we found plastic on 52 out of 71 beaches, the amount of large microplastics in the North Sea and Baltic Seas was lower than in other studies,” explains Bruno Walther. “If we had also analyzed smaller microplastic particles, we would certainly have found much higher concentrations,” adds Melanie Bergmann. In previous AWI studies in the North Sea and the Arctic, microplastics smaller than one millimeter accounted for over 90 per cent of the microplastics found in sediments. “We also randomly selected sampling sites on the beach, rather than focusing on accumulation areas such as drift lines.” This may also explain differences.

Of the 1139 samples analyzed, 177 contained a total of 260 plastic particles. This is an average of about four plastic particles per square meter. On a ten-hectare beach, that would be 400,000 plastic particles. However, the analysis also shows that microplastic pollution varies greatly from place to place.

How effective are policies, and where do policies need to be re-adjusted?

“Our study is the first to provide comparable data on the large-scale distribution of plastic pollution along the entire German coast using standardized methods,” emphasizes Melanie Bergmann. This is necessary, for instance, to be able to map the status quo against the success of future policies to limit plastic pollution. For example, monitoring results suggest that legislative changes may have led to fewer plastic bags being found on the seafloor in north-west Europe over the past 25 years. “But we need stronger, science-based policies that set binding rules on how we avoid, reduce and recycle plastics.” This would include measures to limit the production and use of plastics to essential applications, to ban hazardous ingredients, to increase degradability in nature and thereby enable the circular use of fewer resources.

“Microplastic Detectives” also shows that monitoring programs that involve citizens to collect comprehensive and timely data collection are successful. Interest in supporting science to tackle plastic pollution is huge: “We were surprised by the number of citizen scientists who enthusiastically spent several hours on the beach, diligently collecting, packing and sending samples. We would like to express our heartfelt thanks for this,” says Bruno Walther. “The ideal outcome of our project would be, to use it as a blueprint for long-term and even more intensive monitoring of microplastics pollution on German beaches,” adds Melanie Bergmann. “This is the only way we can review and adapt the measures we urgently need to turn the tide on plastics and their negative impacts on our coastal environment, tourism and human health.” The “Microplastic Detectives” project has now come to an end. However, citizens can still get involved in campaigns such as the Plastic Pirates citizen science project, which has school children collecting data on plastic pollution on coasts and rivers.

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Journal

Frontiers in Environmental Science

DOI

10.3389/fenvs.2024.1458565 

Method of Research

Data/statistical analysis

Article Title

Microplastic detectives: a citizen science project reveals large variation in meso-and microplastic pollution along German coastlines

Article Publication Date

25-Sep-2024

 

Atmospheric microplastic transport predominantly derived from oceans, study finds

by Hannah Bird , Phys.org

a) Illustration of the global microplastic cycle with sources in the built environment

 dispersing them through rivers and oceans via aquatic or airborne wind transport before

 deposition by gravity and precipitation. b) Illustration of microplastics deposition depending

 upon size and shape, with smaller spherical particles transported further. c) Images of 

microplastic fibers used in this study. 

Credit: Nature Geoscience (2023). DOI: 10.1038/s41561-023-01264-6

Microplastics in our natural environments are of increasing concern as these tiny particles (<5mm diameter) pollute ecosystems, posing issues to the well-being of animals and humans alike. There are two principal categories of microplastics: primary particles are manufactured for their size and originate from consumer products, such as the microbeads used in cosmetics, while secondary microplastics occur due to the breakdown of larger materials, such as plastic water bottles and matter from industrial waste.

This breakdown occurs due to ultraviolet radiation from the sun causing plastic to become brittle and thus susceptible to the erosive action of waves in particular to shear off flakes into the surrounding environment.

Their longevity during decomposition, taking upwards of 500 years to complete in a landfill, is a critical factor of their detrimental impact on habitats. Marine animals ingest microplastics suspended in the ocean, and microplastics mixed with the sand on our beaches is barely noticeable. Research has discovered microplastics in the smallest plankton all the way through to filter feeding giants of the sea—whales.

But it is not just the ocean that transports these tiny particles across the globe. Atmospheric wind regimes can carry microplastics vast distances, and their shape has a critical impact on airborne retention before deposition.

New research published in Nature Geoscience considers a theory-based model to determine the settling velocity (the point at which a particle stops being suspended in air and settles due to gravity) of microplastics of various sizes and shapes (up to 100μm long and down to 2μm wide), as compared to previous research that has assumed spherical microplastics. The effect of air turbulence on settling velocity was also factored to determine long distance transport.

Dr. Shuolin Xiao, of Cornell University in New York, and colleagues found that flatter microplastics had overestimates of their dry atmospheric deposition rate under the traditional spherical particle model compared to their newer model, as well as enhanced residence times in the environment >450%. Consequently, this research highlights that microplastics are likely to travel farther than previously thought through atmospheric wind regimes, and therefore deposit over a much larger area. However, by modeling their atmospheric transport it may be possible to determine source locations to aid management plans and reduce further dispersal.

The research team used experimental data on the settling of nylon fibers alongside the model and concluded that very thin and long microplastic fibers would be particularly abundant in both natural and urban environments, being deposited sooner and closer to the source and have greater longevity in ecosystems than spherical particles. The irregularity of air turbulence was found to impact elongated microplastic fibers more than spherical ones as it alters transport orientations and therefore settling velocity due to its weight and air resistance.

This model validates previous work published in Science by Dr. Janice Brahney, Associate Professor at Utah State University, and collaborators who had collected microplastic samples from national parks across the United States. Evaluating a total of 1,260 length and width measurements alongside microplastic fiber shapes, the team determined that these fibers, predominantly derived from clothing, contributed to more than 1,000 metric tons of microplastics deposited by wind and rain within the south and central western United States alone annually.

Estimates of the percentage contribution of key microplastic fiber sources of atmospheric transport: from tires, those entrained from the ocean surface, agricultural and anthropogenic dust, plus general population sources in daily use. Credit: Nature Geoscience (2023). DOI: 10.1038/s41561-023-01264-6

With this knowledge, the research team then considered a number of key sources of microplastics carried by atmospheric transport: particles from roads and tires, particles picked up by wind from the surface of the ocean, dust from agricultural practices (likely from the application of wastewater that contains microbeads from cosmetic and cleaning products) and urban activities, and the vast array derived from the population globally.

Based on the model, deposition of flat fibers from tires were reduced compared to previous models, while those derived from the ocean had increased. Dust from agriculture and urban activities as well as the overall anthropogenic sources in daily use was found to be less impactful. The exact mechanism by which microplastics in the ocean become airborne does however require further investigation, particularly as this appears to be a dominant source.

While some remote areas of the planet may be considered "pristine" and protected from direct human interaction, this research highlights that our fingerprints can still be found in far-reaching locations, and the toll of plastic consumption now will continue to be felt over generations to come if high-risk forms are not sufficiently managed.

More information: Shuolin Xiao et al, Long-distance atmospheric transport of microplastic fibres influenced by their shapes, Nature Geoscience (2023). DOI: 10.1038/s41561-023-01264-6

Journal information: Nature Geoscience , Science  

© 2023 Science X NetworkScientists reveal the transportation mechanism of atmospheric microplastics