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Understanding Plastic Pollution: The contribution from clothing, and the fate of plastics further up the food chain

PLOS ONE is delighted to introduce a new Curated Collection – Recent Advances in Understanding Plastic Pollution. This global challenge may have not been the biggest fixture in the media during the past couple of years, but researchers, governments, volunteers and the public have all been working hard on ensuring that it is easier than ever to be a part of the movement to reduce plastic pollution. Many of us will now be used to receiving take-away food in paper bags or boxes and being equipped with wooden forks and spoons instead of the traditional plastic ones. The PLOS ONE community of researchers working on plastic pollution have been busy reporting new results on identifying microplastic prevalence in various organisms and habitats, understanding how members of the public understand recycling and bioplastics, and how clothes shed microfibers during washing and drying. You can learn more about all of this in our new Curated Collection.

In this first installment of our Q&A with authors from this collection, we speak to some of our researchers working on how clothes may contribute to microfiber pollution during washing and drying, and a group of researchers collating the evidence on how plastics accumulate in marine species.

Kirsten Kapp, Professor, Central Wyoming College and Rachael Zoe Miller, Founder, Rozalia Project for a Clean Ocean

Kirsten Kapp is a professor of biological sciences at Central Wyoming College. She began teaching for the college in 2007 after earning degrees in Wildlife and Fisheries Management and Conservation Biology and Sustainable Development. Her interest in wildlife-human coexistence and human interactions with the environment has fueled her research focus to date, from studying wildlife management issues in Kenya, to investigating human-black bear conflicts and microplastics pollution. She began researching microplastic pollution primarily in freshwater environments in 2014. Kapp is an active member of the NIH-funded Wyoming INBRE Network, whose mission is to strengthen biomedical research while creating research opportunities for undergraduate students.

Rachael Zoe Miller is an expedition scientist, National Geographic Explorer and Explorers Club Fellow working to protect the ocean. She is the Founder of Rozalia Project for a Clean Ocean, a nonprofit addressing marine debris and co-inventor of the Cora Ball, the world’s first microfiber-catching laundry ball. Rachael leads teams on expeditions whose scientific results are published in peer-reviewed journals and education programs that inspire thousands of all ages. She’s presented worldwide including at TedX and The Explorer’s Club. Rachael captained the 60’ sailing research vessel, American Promise, trained Navy SEALS to use underwater robots, and mentors young scientists at the New York Harbor School.

Kirsten Kapp’s and Rachael Zoe Miller’s paper in this Curated Collection: Kapp KJ, Miller RZ (2020) Electric clothes dryers: An underestimated source of microfiber pollution. PLoS ONE 15(10): e0239165.

PLOS: Your study is unusual in many ways, as it was conducted during lockdown. In fact, I remember being really fascinated by it when it was first submitted – the pink fleeces and the fresh snow. Can you tell us more about the background to this study? Was it something you had planned to do in the lab, but then adapted to lockdown?

KK and RZM: In 2016, we were among the first to conduct whole river studies investigating microplastics on the water’s surface, Kirsten on the Snake River and Rachael on the Hudson River. Despite the differences in these river systems, our results showed similar concentrations and types (both containing more microfibers than any other type of microplastics) and both studies showed no statistical relationship between population centers or waste water treatment plants and microplastic/microfiber concentration. As we discussed our findings, we realized that both studies indicated sources beyond wastewater treatment plants which, at that time, were the accepted primary source for microfibers. During one memorable conversation considering possible additional sources, such as electric dryers and how much skiing we both might get to do that winter, Rachael shared her observations of fiber covered foliage under her dryer vent. This led to our mutual ‘aha’ moment – that snow would allow us to measure microfiber pollution much easier than collecting soil samples. Rather than having to digest heaps of organic matter in soil samples to isolate microplastics, we could treat snow samples just like the hundreds of water samples with which we were already familiar.

Between that conversation and the study we would eventually publish in PLOS ONE, one of Kirsten’s NIH-funded Wyoming INBRE research students conducted preliminary investigations by analyzing snow samples for microfibers outside of household dryer vents in a community setting. While this study certainly indicated that we were onto something in terms of there being emissions, understanding the specifics was extremely difficult with so many variables – amount, type, age and colors of fabrics, location and accessibility of dryer vents, whether the dryer vents and lint traps were cleaned, the settings used, any additives used (such as dryer sheets, fabric softeners, etc.) and the details about the dryer models and installations themselves. This, along with inspiration from microfiber studies in washing machines, led us to our study design. For example, McIlwrath et al used bright pink polyester blankets, which we realized would work perfectly for both households since neither of us wore garments of the same color at either of our homes. Using this unique color helped to ensure that the pink fibers observed in snow samples were from our test blankets and not from other household textiles. They were also very obvious under the microscope and easy to distinguish from organic matter in the samples.

Our study was conceived before COVID, designed just as it was emerging as a global pandemic and executed during lock-down. From the start, our goal was to investigate a direct link between dryer exhaust and the environment in an accessible way that could be replicated by other people. We were fortunate in that we both had access to the equipment necessary to collect, process and analyze the samples.

PLOS: There must have been a range of challenges that were quite different from “normal” lab work or field work. Was there anything particularly challenging or rewarding? Was there any point where you wondered whether it would all come together?

KK and RZM: Absolutely, we experienced challenges, especially during sample collection. For example, we had to ensure ‘clean’ sampling areas free from wildlife interference (for example the deer, elk and moose that wander through), which we solved by fencing off the areas. We also needed at least 3 inches of fresh snow and little- to-no wind for each of our tests. That is hard to guarantee in our mountain areas! We were definitely nervous about getting that combo at the right times before spring (uncooperative weather could have delayed our research by 9-10 months). Furthering our concern was the fact that we decided to consider the first version of our sample collection as practice which meant we needed 3 of these “perfect” days starting in late-February. Both locations had a full thaw before our last sample days – at times we were sitting on the edges of our seats hoping for the perfect winter’s day.

PLOS: You studied how clothes shed during the use of a dryer, and research exists on microfiber release during washing. We also know that clothes shed microfibers whilst we wear them. Do we know how the microfiber release for a certain garment differs during washing vs drying vs wearing?

KK and RZM: At this point, there are a good handful of studies that look at how different textile materials and weave types shed in washing machines. Fewer studies address this with dryers and even fewer with wearing. Rachael co-authored a paper with Dr. Claire Gwinnett establishing the amount of contamination field researchers garments contribute to water samples (Gwinnett and Miller 2021) simply by wearing them. Rachael describes the findings from that paper as ‘We are all Pigpen (from the Peanuts cartoon), but instead of walking around in a cloud of dirt, it is more likely we are walking around in a cloud of microfiber.”

It is important for future research to address microfiber shedding during the entire wash and dry process, and to identify the factors that contribute most to the shedding of microfibers. This type of research will inform the development and deployment of solutions to this problem.

PLOS: Several other studies in this Collection also look the effects of plastic pollution on living species. One of these is “Lant NJ, Defaye MMA, Smith AJ, Kechi-Okafor C, Dean JR, Sheridan KJ (2022) The impact of fabric conditioning products and lint filter pore size on airborne microfiber pollution arising from tumble drying. PLoS ONE 17(4): e0265912.” Has seeing these other research studies in the collection helped inspire any thoughts about future work you might do, or other advances your research community will make?

KK and RZM: Lant et al’s work is exactly the type of research we hoped would follow our own study and is a great advancement in this field of research. As many studies do, ours left us with more questions than answers, and Lant and his team addressed some of those questions. We aim to conduct research that sets the foundation for the development of robust solutions, ideally preventative ones, to the problem of microfiber pollution from fiber fragmentation. We are hopeful and confident that more research will come forward informing everyone from textile manufacturers, clothing designers, washer and dryer manufacturers and consumers alike, inspiring solutions that work to protect our environment from microfiber pollution. As for the two of us, stay tuned, we have a shared love of science, snowsports and protecting our planet from microplastics, and we have some ideas for future study percolating!

Neil Lant, Research Fellow, Procter & Gamble

Dr Neil Lant joined Procter & Gamble’s Newcastle Innovation Centre in 1997 after completing a chemistry degree and PhD in bioorganic chemistry. For the past 25 years he has worked in fabric and home care product development for all regions of the world, with a strong emphasis on applying new enzyme technology to improve product performance and sustainability, resulting in over 150 families patent applications. He also leads P&G’s microfiber research program, as part of his broader interests in the role of fabric care products in improving textile sustainability.

Neil Lant’s paper in this Curated Collection: Lant NJ, Defaye MMA, Smith AJ, Kechi-Okafor C, Dean JR, Sheridan KJ (2022) The impact of fabric conditioning products and lint filter pore size on airborne microfiber pollution arising from tumble drying. PLoS ONE 17(4): e0265912.

PLOS: You studied microfiber shedding from clothes during various washing and drying conditions. You made a distinction between European and North American washing routines. What is the main difference between these? How do they differ from those in other parts of the world that were not studied?

NL: The washing machines used in Europe are almost exclusively front-loaders with a wash water volume of around 13 litres. However, in North America several very different appliance types are being used, broadly falling into three types – (i) front loaders that are essentially larger versions of European machines, (ii) traditional top-loading machines that have a large water volume of around 64 litres and (iii) high efficiency top-loading machines with a water volume of around 32 litres. We have found that microfiber release is driven by many factors but our previous publications were the first to recognise that the ratio of water volume to fabric weight was particularly important with high water to fabric ratios causing the highest levels of release. For this reason we run testing in both European and top-loading North America machines to check that the same trends are observed in very different conditions. Other appliance types are used in different regions of the world, and many consumers still wash by hand, but the European and North American washing machines are good representatives of those used in markets where tumble drying is common, as in this paper we were mainly interested in microfiber release during the drying step.

PLOS: You mention in this study that the only real solution to microfiber shedding may be to design a completely different type of dryer. What would need to be the key differences, and how close are we to being able to developing something like that?

NL: The study was focused on airborne microfiber pollution arising from vented dryers which have a air duct to the outside of the building, which is the most important type of dryer in North America with over 95% of the market. The airborne microfiber release can be eliminated by either improving the removal of fibers from that air flow (e.g. using the cyclonic filtration process used in many vacuum cleaners) or moving to fully sealed condenser dryers that collect all fibres and moisture within the appliance. The only problem with the latter is that the fibers can end up in the condensed water or on the condenser which is typically washed in a sink, running the risk of solving an air pollution issue by increasing water pollution! This suggests that we might need to redesign all tumble dryers to ensure that all fibers can be collected and disposed in household waste, with no opportunity for fibers to be released to the air or water.

Chimdia Kechi-Okafor, co-author of this study in PLOS ONE, inspects one of the filters used to better understand microfiber shedding during tumble drying. Chimdia Kechi-Okafor is a PhD student in Fibre Evidence at Northumbria University.

PLOS: You studied how clothes shed during washing and drying. We also know that clothes shed microfibers whilst we wear them. Do we know how the microfiber release for a certain garment differs during washing vs drying vs wearing?

NL: Forensic scientists have known for a long time that fabrics lose fibers when they make contact with other surfaces, but loss of fibers to the air and their transfer to other surfaces has now been proven. We also know that fibers will be lost during line drying of clothes. Although textile scientists are gaining a better understanding of the relationship between fiber, yarn, and textile construction and microfiber shedding during washing, more research will be needed to understand whether the same principles apply to other modes of microfiber release. And we still don’t have a clear understanding of the relative quantities of microfibers being released from textiles to air and water from these sources nor the ultimate fate of these fibers. However, there is a clear consensus that steps to reduce the intrinsic ‘sheddability’ of clothing will be a move in the right direction and we anticipate future government legislation to drive any changes needed in textile manufacturing, in line with proposed legislation in several markets to include microfiber filters in new washing machines.

PLOS: Several other studies in this Collection also examine the effects of plastic pollution on living species. One of these is “Kapp KJ, Miller RZ (2020) Electric clothes dryers: An underestimated source of microfiber pollution. PLoS ONE 15(10): e0239165.” Has seeing these other research studies in the collection helped inspire any thoughts about future work you might do, or other advances your research community will make?

NL: Kapp and Miller’s article was a breakthrough in being the first to recognise, and begin to quantify, the contribution of vented tumble dryers to airborne (and subsequent terrestrial) pollution. Their methods involving use of snow to collect deposited microfibers were fantastic. As their study only involved two dryers and didn’t measure the relative quantities of microfibers being released during washing and drying, we were keen to build on that study with a more extensive program spanning different markets, impact of fabric care products, and evaluating some potential solutions. The quantity of literature focused on tumble drying is still very limited so we would like to continue researching this area with an emphasis on condenser dryers which are already very common outside of North America and, when integrated with heat pump technology, are much more energy efficient resulting in lower operating costs and reduced carbon footprint.

Michaela Miller, PhD student, James Cook University and the Australian Institute of Marine Science

I have recently completed my PhD in Marine biology at James Cook University and the Australian Institute of Marine Science (AIMS), focused on the ecological impact and fate of microplastics on the Great Barrier Reef, Australia. Originally from Connecticut, USA, I moved to Australia almost seven years ago in pursuit of conducting research on the Great Barrier Reef and in search of the laid-back lifestyle Australians emulate. Since then, I have had the pleasure of partaking in world-class research at AIMS, both through my studies and as a research technician with the Microplastics Team. Outside of work, you can find me hiking, camping, swimming in the ocean, or taking my dog, Daisy, for a run.

Michaela Miller’s paper in this Curated Collection: Miller ME, Hamann M, Kroon FJ (2020) Bioaccumulation and biomagnification of microplastics in marine organisms: A review and meta-analysis of current data. PLoS ONE 15(10): e0240792.

PLOS: You performed a meta-analysis to consolidate the evidence for bioaccumulation and biomagnification of microplastics in marine organisms. What motivated you to undertake this study right now – are we at a significant time point in accumulating evidence?

MM: Yes, we are at a pivotal movement in time within the microplastics and plastic pollution field in general. A time where studies, experiments and reports are increasing exponentially in hopes of understanding the extent, determining effects, and addressing knowledge gaps surrounding a contaminant of emerging concern: microplastics. These goals motivated the meta-analysis on bioaccumulation and biomagnification of microplastics. As the field of plastic pollution advances and builds upon itself, one question that scientists, especially the team I am part of at the Australian Institute of Marine Science, keep coming back to is, “what is the ecological impact of microplastics?” Yet, this is a difficult question to answer, complicated by microplastics not being a simple contaminant, and instead a complex cocktail comprised of various polymers, colours, sizes, shapes, and chemical additives. Therefore, to try and address this question we set out to see if certain ecological endpoints, such as bioaccumulation and biomagnification can be applied to microplastic research.

Despite thousands of scientific manuscripts observing, detailing, and testing microplastic ingestion, both in the marine environment and under simulated laboratory conditions, this fundamental question is still in its infancy. Claims are often made of accumulation and the potential for microplastics or associated chemical additives to magnify up the food web by means of trophic transfer; yet all these claims had been speculation at the conception of the study. So, we aimed to determine if all published reports of microplastic ingestion and chemical additive uptake, both from field collections and laboratory experiments, support these claims – if microplastics or chemical additives accumulate and magnify, we would see an increase alongside trophic level.

PLOS: You found that it is possible that biomagnification of microplastics may not fit the same patterns as those we are familiar with for dissolved chemicals. Was this a result you had foreseen? How may we study what these patterns look like for microplastics?

MM: As a scientist, I tend to not anticipate results before conducting a study. However, based on the continuous reading of previous reports of microplastic ingestion in the literature, it was not clear that there was a drastic increase in contamination in higher trophic level organisms. This trend of increased concentration in higher level organisms is one observed for some dissolved chemical contamination like mercury or other heavy metals (e.g., lead, cadmium). Yet, with the field of microplastic pollution in its infancy, scientists are still determining how microplastics interact with marine organisms on an ecological scale. Higher level organisms (e.g., fish, mammals), were not reported to have higher levels of microplastics compared to lower-level organisms (e.g., zooplankton, bivalves), so from a preliminary evidence point of view, we thought this trend would be observed across a general marine food web. What was not anticipated was the ultimate lack of information and reports comparing environmental contamination to marine organism contamination, limiting in-depth assessment of bioaccumulation. This study highlighted substantially more knowledge gaps in relation to the ecological impact and fate of microplastics in a general marine food web.

With plastic research overlapping with ecotoxicology research, given the chemical hazards associated with plastics, this meta-analysis set out to see if these traditional terms applied to dissolved chemical contamination could even be applied to microplastic research. The short answer is there is not enough research done to conclude this. The longer answer is that microplastics interact with marine organisms in a different way to dissolved chemical contamination as they are physical heterogeneous particulate matter ingested, and often staying within the confines of the gastrointestinal tract (small < 10 µm plastics potentially translocating being the exception, of course). While these interactions are different, it does not mean traditional terms such as bioaccumulation and biomagnification cannot be applied to address the ecological impact of plastics. It simply comes with the caveat that we are discussing contamination in a gut through-system, rather than dissolved chemicals within tissues or organs.

Laboratory experiments are demonstrating that the concentration, accumulation, and magnification of microplastics up food webs is possible, yet it is also highlighting that retention times are species-specific and microplastics often pass through during egestion. For microplastics, it may be that retention times are not long enough to result in bioaccumulation or biomagnification of microplastics up the food web. Yet, this field of research is relatively under researched and warrants further focus.

PLOS: You are currently finalising your PhD studies. What has been your experience of publishing your first few papers? Was there anything that you now know that you wish you had known before preparing your first manuscript?

MM: I have, as of 9 September, officially submitted my PhD thesis – which is an exciting milestone in my career! My experience publishing my first few papers is an experience I didn’t anticipate loving as much as I have. The whole process is akin to storytelling, with science and data being the focal point; the story that is told surrounding these data is the juicy bit. Getting into marine science, I was driven by my passion for data collection and figuring things out – gathering the puzzle pieces together so that a bigger picture could be seen. I never anticipated I would actually love the building of the puzzle.

Prior to publishing, or even writing a thesis, I wish someone had sat me down to tell me that just because something makes sense in your head, it does not mean someone will read it the way you intend. One of the biggest struggles I have found as a scientist is that we are often incredibly close to the data or manuscript, having worked on them for years – this makes us often unable to take steps back to see how the work could be interpreted from an outside perspective. Working on a project for a prolonged period of time becomes a bit like a shifting baseline syndrome, certain knowledge starts to become fundamental, and the lines become blurred with what is common knowledge and what is not. At the current point in my professional career, I have found it incredibly useful to keep the research question in focus with everything I write.

PLOS: Several other studies in this Collection also look the effects of plastic pollution on living species. Has seeing these other research studies in the collection helped inspire any thoughts about future work you might do, or other advances your research community will make?

MM: Absolutely! It is quite rare for me to read a paper and not be inspired to conduct future work – I suppose that is a sign that I am in the right profession. The field has made massive strides towards documenting and detailing the presence and persistence of plastics in the marine environment. What used to be doubted as an issue is now considered a contaminant of emerging concern, resulting in ground-breaking global agreements, such as plastic straw and bag bans, united efforts for beach clean-ups and even the United Nations Environment Program (UNEP) Global Plastic Treaty. Yet we still have so far to go in the way of plastic research.

I am constantly inspired to continue the understanding of impacts and effects of plastic on the marine environment and the organisms that inhabit it. Continuously seeing fantastic and novel work being conducted only fuels this desire to continue my work. I hope that moving forward we transition into elucidating impacts (e.g., physical, chemical, biological) and developing feasible mitigation strategies or alternatives to alleviate the issue of plastic pollution.

Stay tuned for more interviews with authors from this collection.

Cover image: Port of Dover, 2014 Beach Clean (CC-BY 2.0)

Disclaimer: Views expressed by contributors are solely those of individual contributors, and not necessarily those of PLOS.

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