Airborne microplastic particle concentrations and characterization in indoor urban microenvironments

Transforming pollution into solutions: A bibliometric analysis and sustainable strategies for reducing indoor microplastics while converting to value-added products

Microplastics (MPs), as emerging indoor contaminants, have garnered attention due to their ubiquity and unresolved implications for human health. These tiny particles have permeated indoor air and water, leading to inevitable human exposure. Preliminary evidence suggests MP exposure could be linked to respiratory, gastrointestinal, and potentially other health issues, yet the full scope of their effects remains unclear. To map the overall landscape of this research field, a bibliometric analysis based on research articles retrieved from the Web of Science database was conducted. The study synthesizes the current state of knowledge and spotlights the innovative mitigation strategies proposed to curb indoor MP pollution. These strategies involve minimizing the MP emission from source, advancements in filtration technology, aimed at reducing the MP exposure. Furthermore, this research sheds light on cutting-edge methods for converting MP waste into value-added products. These innovative approaches not only promise to alleviate environmental burdens but also contribute to a more sustainable and circular economy by transforming waste into resources such as biofuels, construction materials, and batteries. Despite these strides, this study acknowledges the ongoing challenges, including the need for more efficient removal technologies and a deeper understanding of MPs' health impacts. Looking forward, the study underscores the necessity for further research to fill these knowledge gaps, particularly in the areas of long-term health outcomes and the development of standardized, reliable methodologies for MP detection and quantification in indoor settings. This comprehensive approach paves the way for future exploration and the development of robust solutions to the complex issue of microplastic pollution.

Every breath you take: high concentration of breathable microplastics in indoor environments

The widespread presence of microplastics (MPs) in the air and their potential impact on human health underscore the pressing need to develop robust methods for quantifying their presence, particularly in the breathable fraction (<5 μm). In this study, Raman micro-spectroscopy (μRaman) was employed to assess the concentration of indoor airborne MPs >1 μm in four indoor environments (a meeting room, a workshop, and two apartments) under different levels of human activity. The indoor airborne MP concentration spanned between 58 and 684 MPs per cubic meter (MP m-3) (median 212 MPs m-3, MPs/non-plastic ratio 0 - 1.6%), depending not only on the type and level of human activity, but also on the surface area and air circulation of the investigated locations. Additionally, we assessed in the same environments the filtration performance of a type IIR surgical facemask, which could overall retain 85.4 ± 3.9% of the MPs. We furthermore estimated a human MP intake from indoor air of 3415 ± 2881 MPs day-1 (mostly poly-amide MPs), which could be decreased to 283 ± 317 MPs day-1 using the surgical facemask. However, for the breathable fraction of MPs (1 - 5 μm), the efficiency of the surgical mask was reduced to 57.6%.

Microplastics suspended in dust from different indoor environments in Barranquilla, Colombia: Predominant microparticles?

Considering that microplastics (MPs) are classified as ubiquitous pollutants, that air quality affects human health, and that people remain indoors most of the time, the need has arisen to evaluate the exposure to MPs within the suspended dust in indoor environments. With this objective, the present study carried out passive sampling to analyze the precipitation of microparticles in some indoor residential environments (2 apartments) and workplaces (an office, a pastry shop, a gift shop, and a paint shop) in Barranquilla, Colombia. The quantification and physical characterization of microparticles were carried out under a stereomicroscope, and the chemical characterization was carried out by infrared microspectroscopy (μFTIR). The highest average concentration of MPs in the apartments was found in the air-conditioned rooms (1.1 × 104 MP/m2/day), and concerning the workplaces, the gift shop and the paint shop were the spaces with a higher proportion of MPs (6.0-6.1 × 103 MP/m2/day), with polyesters being the main synthetic polymers, but being semi-synthetic particles the predominant among the samples. Regarding its morphology, fibers were the most abundant shape (>90%), grouping mainly in the 1000-5000 μm range, while the few fragments found were mostly grouped below 50 μm. Exposure by inhalation of MPs in adults was estimated between 1.7 × 102-1.6 × 103 MP/kg/day, while by ingestion it ranged between 2.7 × 102-2.4 × 103 MPs/kg/day. On the other hand, within our research, a significant presence of non-plastic microparticles was found, which reached up to 69% in analyzed samples, corresponding mainly to cotton and cellulose, so we suggest that these should also be included in future studies that aim to estimate potential health implications from exposure to suspended micropollutants.

Pyr-GC-Orbitrap-MS method for the target/untargeted analysis of microplastics in air

Pyrolysis-gas chromatography coupled to Orbitrap-mass spectrometry is a novel technique that allows the low level and precise determination of microplastics in environmental samples. In this paper, we develop and assess the target and untargeted performance of Pyr-GC-Orbitrap-MS. The method was optimized for 10 plastic polymers: polymethyl methacrylate, nylon-6,6, polypropylene, nitrile butadiene rubber, polyvinyl chloride, polyethylene terephthalate, acrylonitrile butadiene styrene, polyethylene, polycarbonate, and polystyrene. Standards were home-made using a diamond driller to attain mean sizes within the range of 45-382 µm. A step-by-step optimization of the analytical procedure was carried out. First, accurate mass measurement of each polymer at 60,000 resolution was studied to select the 3 most intense and selective quantification and confirmation ions. Second, internal standard quantification was optimized, and good linearity, repeatability, and reproducibility were obtained. Blank contribution and instrumental detection limit were evaluated for each polymer. Finally, the combined and expanded uncertainty of the Pyr-GC-Orbitrap-MS method was calculated to determine the sources of variation, considering that home-made standards were used. To evaluate method performance, targeted and non-targeted analysis of indoor air samples collected from gyms and department stores were carried out. The Pyr-GC-Orbitrap-MS methodology herein described can be applied for the quantitative assessment of MPs and other substances in different matrices.

Microplastics in water: Occurrence, fate and removal

A global study on tap water samples has found that up to 83% of these contained microplastic fibres. These findings raise concerns about their potential health risks. Ingested microplastic particles have already been associated with harmful effects in animals, which raise concerns about similar outcomes in humans. Microplastics are ubiquitous in the environment, commonly found disposed in landfills and waste sites. Within indoor environments, the common sources are synthetic textiles, plastic bottles, and packaging. From the various point sources, they are globally distributed through air and water and can enter humans through various pathways. The finding of microplastics in fresh snow in the Antarctic highlights just how widely they are dispersed. The behaviour and health risks from microplastic particles are strongly influenced by their physicochemical properties, which is why their surfaces are important. Surface interactions are also important in pollutant transport via adsorption onto the microplastic particles. Our review covers the latest findings in microplastics research including the latest statistics in their abundance, their occurrence and fate in the environment, the methods of reducing microplastics exposure and their removal. We conclude by proposing future research directions into more effective remediation methods including new technologies and sustainable green remediation methods that need to be explored to achieve success in microplastics removal from waters at large scale.

Critical review on airborne microplastics: An indoor air contaminant of emerging concern

Airborne Microplastics (MPs), an emerging environmental issue, have gained recent attention due to their newfound presence in indoor environments. Utilizing the Web of Science database for literature collection, the paper presents a comprehensive review of airborne MPs including emission sources, assessment methods, exposure risks, and mitigation strategies. This review delves into the diverse sources and mechanisms influencing indoor airborne MP pollution, underscoring the complex interplay between human activities, ventilation systems, and the characteristics of indoor environments. Major sources include the abrasion of synthetic textiles and the deterioration of flooring materials, with factors like carpeting, airflow, and ventilation significantly impacting MP levels. Human activities, such as increased movement in indoor spaces and the intensive use of plastic-based personal protective equipment (PPE) post-pandemic, notably elevate indoor MP concentrations. The potential health impacts of airborne MPs are increasingly concerning, with evidence suggesting their role in respiratory, immune, and nervous system diseases. Despite this, there is a scarcity of information on MPs in diverse indoor environments and the inhalation risks associated with the frequent use of PPE. This review also stresses the importance of developing effective strategies to reduce MP emissions, such as employing HEPA-filtered vacuums, minimizing the use of synthetic textiles, and enhancing indoor ventilation. Several future research directions were proposed, including detailed temporal analyses of indoor MP levels, interactions of MP with other atmospheric pollutants, the transport dynamics of inhalable MPs (≤10 μm), and comprehensive human exposure risk assessments.

Micro- and nano-plastics in the atmosphere: A review of occurrence, properties and human health risks

The ubiquitous occurrence of micro/nano plastics (MNPs) poses potential threats to ecosystem and human health that have attracted broad concerns in recent decades. Detection of MNPs in several remote regions has implicated atmospheric transport as an important pathway for global dissemination of MNPs and hence as a global health risk. In this review, the latest research progress on (1) sampling and detection; (2) origin and characteristics; and (3) transport and fate of atmospheric MNPs was summarized. Further, the current status of exposure risks and toxicological effects from inhaled atmospheric MNPs on human health is examined. Due to limitations in sampling and identification methodologies, the study of atmospheric nanoplastics is very limited today. The large spatial variation of atmospheric MNP concentrations reported worldwide makes it difficult to compare the overall indoor and outdoor exposure risks. Several in vitro, in vivo, and epidemiological studies demonstrate adverse effects of immune response, apoptosis and oxidative stress caused by MNP inhalation that may induce cardiovascular diseases and reproductive and developmental abnormalities. Given the emerging importance of atmospheric MNPs, the establishment of standardized sampling-pretreatment-detection protocols and comprehensive toxicological studies are critical to advance environmental and health risk assessments of atmospheric MNPs.

A comprehensive review on the source, ingestion route, attachment and toxicity of microplastics/nanoplastics in human systems

Microplastics (MPs)/nanoplastics (NPs) are widely found in the natural environment, including soil, water and the atmosphere, which are essential for human survival. In the recent years, there has been a growing concern about the potential impact of MPs/NPs on human health. Due to the increasing interest in this research and the limited number of studies related to the health effects of MPs/NPs on humans, it is necessary to conduct a systematic assessment and review of their potentially toxic effects on human organs and tissues. Humans can be exposed to microplastics through ingestion, inhalation and dermal contact, however, ingestion and inhalation are considered as the primary routes. The ingested MPs/NPs mainly consist of plastic particles with a particle size ranging from 0.1 to 1 μm, that distribute across various tissues and organs within the body, which in turn have a certain impact on the nine major systems of the human body, especially the digestive system and respiratory system, which are closely related to the intake pathway of MPs/NPs. The harmful effects caused by MPs/NPs primarily occur through potential toxic mechanisms such as induction of oxidative stress, generation of inflammatory responses, alteration of lipid metabolism or energy metabolism or expression of related functional factors. This review can help people to systematically understand the hazards of MPs/NPs and related toxicity mechanisms from the level of nine biological systems. It allows MPs/NPs pollution to be emphasized, and it is also hoped that research on their toxic effects will be strengthened in the future.

A comprehensive review of micro- and nano-plastics in the atmosphere: Occurrence, fate, toxicity, and strategies for risk reduction

Micro- and nano-plastics (MNPs) have received considerable attention over the past 10 years due to their environmental prevalence and potential toxic effects. With the increase in global plastic production and disposal, MNP pollution has become a topic of emerging concern. In this review, we describe MNPs in the atmospheric environment, and potential toxicological effects of exposure to MNPs. Studies have reported the occurrence of MNPs in outdoor and indoor air at concentrations ranging from 0.0065 items m-3 to 1583 items m-3. Findings have identified plastic fragments, fibers, and films in sizes predominantly <1000 μm with polyamide (PA), polyester (PES), polyethylene terephthalate (PET), polypropylene (PP), rayon, polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polyacrylonitrile (PAN), and ethyl vinyl acetate (EVA) as the major compounds. Exposure through indoor air and dust is an important pathway for humans. Airborne MNPs pose health risks to plants, animals, and humans. Atmospheric MNPs can enter organism bodies via inhalation and subsequent deposition in the lungs, which triggers inflammation and other adverse health effects. MNPs could be eliminated through source reduction, policy/regulation, environmental awareness and education, biodegradable materials, bioremediation, and efficient air-filtration systems. To achieve a sustainable society, it is crucial to implement effective strategies for reducing the usage of single-use plastics (SUPs). Further, governments play a pivotal role in addressing the pressing issue of MNPs pollution and must establish viable solutions to tackle this significant challenge.

Indoor microplastics: a comprehensive review and bibliometric analysis

Indoor microplastic (MP) pollution is becoming a worldwide issue because people spend more time inside. Through dust and air, indoor MP pollution may harm human health. This review summarizes recent advancements in indoor MP research, covering pretreatments, quality control, filter membranes, and identification methods. Additionally, it conducts bibliometric analysis to examine the usage of keywords, publication records, and authors' contributions to the field. Comparatively, dust and deposition samples exhibit higher MP concentrations than indoor air samples. Fiber-shaped MPs are commonly detected indoors. The color and types of MPs display variability, with polypropylene, polyethylene, polyethylene terephthalate, and polystyrene identified as the dominant MPs. Indoor environments generally demonstrate higher concentrations of MPs than outdoor environments, and MPs in the lower size range (1-100 µm) are typically more abundant. Among the reviewed articles, 45.24% conducted pretreatment on their samples, while 16.67% did not undergo any pretreatment. The predominant filter utilized in most studies was the Whatman Glass microfiber filter (41.67%), and MPs were predominantly characterized using µ-FTIR (19.23%). In the literature, 17 papers used blank samples, and eight did not. Blank findings were not included in most research (23 articles). A significant increase in published articles has been observed since 2020, with an annual growth rate exceeding 10%. The keyword microplastics had the highest frequency, followed by fibers. This indoor MP study emphasizes the need for collaborative research, policymaking, and stakeholder involvement to reduce indoor MP pollution. As indoor MP research grows, so are opportunities to identify and minimize environmental and health impacts.

Forecasting global plastic production and microplastic emission using advanced optimised discrete grey model

Plastic pollution has become a prominent and pressing environmental concern within the realm of pollution. In recent times, microplastics have entered our ecosystem, especially in freshwater. In the contemporary global landscape, there exists a mounting apprehension surrounding the manifold environmental and public health issues that have emerged as a result of the substantial accumulation of microplastics. The objective of the current study is to employ an enhanced grey prediction model in order to forecast global plastic production and microplastic emissions. This study compared the accuracy level of the four grey prediction models, namely, EGM (1,1, α, θ), DGM (1,1), EGM (1,1), and DGM (1,1, α) models, to evaluate the accuracy levels. As per the estimation of the study, DGM (1,1, α) was found to be more suitable with higher accuracy levels to predict microplastic emission. The EGM (1,1, α, θ) model has slightly better accuracy than the DGM (1,1, α) model in predicting global plastic production. Various accuracy measurement tools (MAPE and RMSE) were used to determine the model's efficiency. There has been a gradual growth in both plastic production and microplastic emission. The current study using the DGM (1,1, α) model predicted that microplastic emission would be 1,084,018 by 2030. The present study aims to provide valuable insights for policymakers in formulating effective strategies to address the complex issues arising from the release of microplastics into the environment and the continuous production of plastic materials.

Characterization of microplastics in the atmosphere of megacity Tehran (Iran)

In this study, the characteristics of ambient airborne microplastics were investigated in Tehran to obtain insights into their origins. For this purpose, sampling operations took place at locations with different backgrounds in summer and autumn by using TSP and PM10 high-volume samplers. As a result of microscopic analysis and Raman spectroscopy, the color, shape, number, size, and type of microplastic particles were investigated. Seven types of chemical structures were identified in the particles, among which polypropylene (18.7%) in summer and polystyrene (20%) in autumn had the dominant share. The average number of particles collected using the TSP and PM10 samplers were 1165 ± 147.64 and 1006.5 ± 147.64, respectively. The size of microplastic particles in different stations varied between 4 and 3094 μm. In the seasonal examination of the identified colors, black (38-43%), red (17-19%), gold (13-14%), brown (12% in both seasons), blue (7-10%), yellow (3-5%), and green (2-5%) had the largest proportions, respectively. The examined microplastics were in three forms: fiber, bead, and fragment, among which the predominant form was fiber, and the most infrequent particles were fragments. Statistical comparisons showed that the sampling location does not have a significant effect on the number and size of particles (p value > 0.05). The season was not identified as a determining parameter for particle size (p value > 0.05). On the other hand, seasonal changes can have a tremendous effect on the microplastic particle number (p value < 0.05). Lastly, to obtain more detailed information about the origin of these particles, continuous and long-term monitoring near known industries and suspected sources of plastic materials and source apportionment studies were suggested.

Online study of the plasma-accelerated aging process and toxicity of polyethylene terephthalate

Plastic aging occurs in all environmental media and affects their environmental behavior and toxicity. In this study, non-thermal plasma was applied to simulate the aging process of plastics, with polyethylene terephthalate (PET-film) being used as a model. The surface morphology, mass defects, toxicity of aged PET-film and the generation of airborne fine particles were comprehensively characterized. The surface of PET films began to become rough and then gradually became uneven, generating pores, protrusions and cracks. The toxicity of aged PET films was assessed in Caenorhabditis elegans which significantly reduced head thrashing, body bending and brood size. A single particle aerosol mass spectrometry instrument was used to characterize the size distribution and chemical composition of airborne fine particles in real-time. Few particles were observed during the first 90 min, while the generation of particles accelerated significantly after aging time beyond 90 min. For two pieces of PET film with surface area of 5 cm2, during the 180 min, at least 15113 ± 153 fine particles were generated, having a unimodal size distribution with a peak of 0.4 µm. The main components of these particles included metals, inorganic non-metals, and organic components. The results provide useful information on plastic aging and are beneficial in assessing the potential environmental risks.

New evidence of the presence of micro- and nanoplastic particles in bronchioalveolar lavage samples of clinical trial subjects

This is the first study reporting the presence of airborne nano-sized plastic particles in the bronchoalveolar lavage fluid (BALF) samples of patients undergoing diagnostic bronchoscopy. The results represent the plastic pollution content in the lower airways of the residents of Northern Europe. Airborne micro- and nanoplastic particles (MP/NPs) are widely dispersed worldwide and intrude on human organisms to various extents, with the respiratory tract being the first line of exposure. The amounts of inhaled MP/NPs, their fate in the human respiratory tract, and the effects on the health of human airways and other exposed organs remain largely unknown. In this clinical study, human BALF samples were assessed by means of optical and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (TEM-EDX). Results show that MP/NPs levels vary in the interval of 0.14-12.8 particles per 100 ml of BALF and are present in all samples tested, mainly in a fragmented form. External pollution by MP/NPs was excluded by carefully choosing methodology and equipment. This finding is a timely addition of valuable information and stimulates further research into the biological effects of inhaled MP/NPs.

Microplastics exposure and immunologic response

OBJECTIVE

To assess the impact of microplastics (MPs) on human health.

DATA SOURCE

The authors conducted a non-systematic review of articles published in English, Portuguese, French, and Spanish in the last decade in the following databases: PubMed, Google Scholar, EMBASE, and SciELO. The keywords used were: microplastics OR nanoplastics OR marine litter OR toxicology OR additives AND human health OR children OR adults.

DATA SUMMARY

MPs are a group of emerging contaminants that have attracted scientific interest and societal attention in the last decade due to their ubiquitous detection in all environments. Humans can primarily be exposed to MPs and nanoplastics via oral and inhalation routes, but dermal contact cannot be overlooked, especially in young children. The possible toxic effects of plastic particles are due to their potential toxicity, often combined with that of leachable additives and adsorbed contaminants.

CONCLUSIONS

Unless the plastic value chain is transformed over the next two decades, the risks to species, marine ecosystems, climate, health, economy, and communities will be unmanageable. However, along with these risks are the unique opportunities to help transition to a more sustainable world.

Microplastics: Human exposure assessment through air, water, and food

BACKGROUND

Microplastics (MP) are plastic particles with dimension up to 5 mm. Due to their persistence, global spread across different ecosystems and potential human health effects, they have gained increasing attention during the last decade. However, the extent of human exposure to MP through different pathways and their intake have not been elucidated.

OBJECTIVES

The objective of this review is to provide an overview on the pathways of exposure to MP through inhalation, ingestion, and dermal contact considering data from the open bibliography on MP in air, dust, food, water and drinks.

METHODS

A bibliographic search on Scopus and PubMed was conducted using keywords on MP in outdoor and indoor air, indoor dust, food including beverages and water and human intake (n = 521). Articles were sorted by their title and abstract (n = 213), and only studies reporting MP identification and quantification techniques were further considered (n = 168). A total of 115 articles that include quality assurance and quality control (QA/QC) procedures are finally discussed in the present review. Based on MP concentration data available in literature, we estimated the potential inhaled dose (ID), dust intake (DI), the estimated daily intake (EDI) via food and beverages. Finally, the total daily intake (TDI) considering both inhalation and ingestion routes are provided for adults, infants and newborns.

RESULTS

The concentrations of MP in outdoor and indoor air, dust, and in food and water are provided according to the bibliography. Human exposure to MP through dust ingestion, inhalation of air and food/drinks consumption revealed that indoor air and drinking waters were the main sources of MP.

CONCLUSIONS

This study reveals that humans are constantly exposed to MP, and that the indoor environment and the food and water we ingest decisively contribute to MP intake. Additionally, we highlight that infants and newborns are exposed to high MP concentrations and further studies are needed to evaluate the presence and risk of MP in this vulnerable age-population.

Nasal lavage technique reveals regular inhalation exposure of microplastics, not associated from face mask use

During the COVID-19 pandemic, the use of face masks has been a worldwide primary protection measure to contain the spread of the virus. However, very little information is known about the possible inhalation of microplastics (MP) from wearing masks. This pilot study evaluates the presence of MP accumulated in nasal cavities through the nasal lavages technique. Six different commercial face masks were tested in 18 participants during five working days (8 h use/day). Eight different polymers (polystyrene, polyamide, poly(ethylene - propylene) diene monomer, polyester, polyethylene, polyvinylidene fluoride, polypropylene, and polyvinyl chloride) predominantly within the 20-300 µm size were detected in nasal lavages, with an average concentration of 28.3 ± 15.6 MP/5 mL nasal solution. Results demonstrate that MP in the nasal cavity are not associated to face mask use but rather to general exposure to airborne MP. We highlight the use of nasal lavages to evaluate human inhalation of MP and associate it to potential sources and risks.

Sentinel supervised lung-on-a-chip: A new environmental toxicology platform for nanoplastic-induced lung injury

Nanoplastics are prevalent in the air and can be easily inhaled, posing a threat to respiratory health. However, there have been few studies investigating the impact of nanoplastics on lung injury, especially chronic obstructive pulmonary disease (COPD). Furthermore, cell and animal models cannot deeply understand the pollutant-induced COPD. Existing lung-on-a-chip models also lack interactions among immune cells, which are crucial in monitoring complex responses. In the study, we built the lung-on-a-chip to accurately recapitulate the structural features and key functions of the alveolar-blood barrier while integrating multiple immune cells. The stability and reliability of the lung-on-a-chip model were demonstrated by toxicological application of various environmental pollutants. We Further focused on exploring the association between COPD and polystyrene nanoplastics (PS-NPs). As a result, the cell viability significantly decreased as the concentration of PS-NPs increased, while TEER levels decreased and permeability increased. Additionally, PS-NPs could induce oxidative stress and inflammatory responses at the organ level, and crossed the alveolar-blood barrier to enter the bloodstream. The expression of α1-antitrypsin (AAT) was significantly reduced, which could be served as early COPD checkpoint on the lung-chips. Overall, the lung-on-a-chip provides a new platform for investigating the pulmonary toxicity of nanoplastics, demonstrating that PS-NPs can harm the alveolar-blood barrier, cause oxidative damage and inflammation, and increase the risk of COPD.

Quantification and identification of airborne small microplastics (<100 μm) and other microlitter components in atmospheric aerosol via a novel elutriation and oleo-extraction method

The atmosphere is a significant pathway for distributing plastic particles and other micro-litter particles from their sources to other environmental compartments. There is a big gap regarding the standardized method for the quantification and identification of airborne microplastics (MPs), especially those in the range of 5-100 μm (small microplastics, SMPs) and airborne micro-litter components (MLCs), i.e., plastic additives, natural fibers and non-plastics synthetic fibers. This study aimed to develop and optimize a pre-treatment method (i.e., elutriation, oleoextraction, and purification) to extract SMPs and MLCs simultaneously from urban aerosol samples. The quantification and simultaneous chemical characterization were performed via Micro-FTIR. The method developed was then applied to two samples from different seasons, i.e., summer and late fall - winter. Micro-litter particles followed the Poisson distribution, and the fiducial limit (confidence interval) was calculated accordingly. Non-parametric statistical tests were performed to evaluate significant differences among the samples. The most abundant plastic polymers were polyethylene (HDPE) and polytetrafluoroethylene (PTFE). Among MLCs, flame retardants, UV filters, stabilizers, and rayon were identified. The results of this study will contribute significantly to establishing standardized and accredited methods to quantify and identify airborne SMPs and MLCs.