Emission of airborne microplastics from municipal solid waste transfer stations in downtown

Treatment and prediction of wastewater from waste transfer station in the eastern rural area of China by a combined system of anaerobic-oxic-anoxic-oxic, coagulation and adsorption

In this study, a combined system of anaerobic-oxic-anoxic-oxic, coagulation and adsorption (AOAOCA) was used to treat the real waste transfer station (WTS) wastewater. The effects of hydraulic retention time (HRT), sludge reflux ratio (SRR), mixed liquid reflux ratio (MLRR), coagulant and zeolite on the contaminants removal efficiency were investigated. When the AOAOCA system was operated at the optimal conditions (HRT of 8 d, SRR of 70%, MLRR of 200%, PAFC as coagulant with dosage of 750 ppm and 1-3 mm zeolite with filling rate of 60%), the effluent COD, NH3-N and TP could reach 82.5 mg/L, 3.7 mg/L and 1.8 mg/L with the highest removal rates of 98.7%, 99.4% and 98.8%, respectively. The effluent of AOAOCA system could meet the "Pollution Control Standard for Domestic Garbage Landfill of China" (GB16889-2024). The greatest contribution to the COD, NH3-N and TP removal rates were from the anaerobic-oxic-anoxic-oxic process (91.2%-97.4%), while the contribution of coagulation and zeolite were 1.8%-6% and 0.8%-2.8%, respectively. The operating cost for WTS wastewater treatment by the proposed AOAOCA system was 17.72 RMB/t based on the costs for electricity, reagent and tap water consumption. The XGBoost model could be effectively used to predict the effluent of the proposed AOAOCA. This study could provide a highly feasible reference about the treatment of WTS wastewater for practical application.

A review of airborne micro- and nano-plastics: Sampling methods, analytical techniques, and exposure risks

Atmospheric Micro- and nano-plastics (MNPs) can be easily inhaled and ingested by humans and have become a global health concern. With the development of instruments and techniques, an increasing number of sampling and analytical methods have been applied to study airborne MNPs. Active samplers and passive collectors are used to collect suspended aerosols and atmospheric depositions. Microscopes and scanning electron microscopy (SEM) have been used to physically identify the MNPs, while Fourier transform infrared (FTIR), Raman spectroscopy, and Pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) are used to identify the polymer compositions of the MNPs. However, the diversity of methods and strategies has greatly limited our ability to compare results and assess exposure risks. In this review, we extracted data from PubMed, Embase, and Scopus from 2018 to 2024 that reported sampling methods, analytical techniques, and abundance/deposition of airborne MNPs. Through a systematic review of the included 140 articles, we emphasized the advantages and limitations of different methods for collecting and analyzing airborne MNPs. In addition, we provided an in-depth analysis of the performance of specific methods across different airborne environments. Furthermore, the current knowledge regarding the abundance, deposition, exposure risks of airborne MNPs, and exposure risk assessment models has been discussed. Finally, we provide concrete recommendations for standardization of methods. This review identified knowledge gaps and recommended future research directions for exposure assessment of airborne MNPs.

Microplastics in glaciers of Tibetan Plateau: Characteristics and potential sources

Microplastics (MPs) in glaciers of remote areas are a hot topic linking the global transport of atmospheric MPs. The Tibetan Plateau (TP) holds large volume of glaciers, providing an effective way to trace MPs transport. Moreover, MPs in glaciers may have adverse effects on the local ecosystem and human health. In this study, we investigate MPs in snowpits collected from six glaciers across the different domain of the TP. The average abundance of MPs in six snowpits is 339.22 ± 51.85 items L-1 (with size ≥10 μm) measured by Agilent 8700 Laser Direct Infrared Chemical Imaging System (LDIR), represented by relatively high MPs abundance in the southern TP and low in the northern TP. The polymers with lower density, namely polyethylene (PE), polyamide (PA), and rubber, are the main MPs types, which are predominated by fragments with sizes smaller than 100 μm in each snowpit. Sources of MPs on glaciers include local tourism and vehicle traffic emissions of MPs. Meanwhile, long-range atmospheric transport of MPs from surrounded regions cannot be ignored. Backward trajectory analysis indicates cross-boundary transport of atmospheric MPs from South Asia play an important role on MPs deposited onto TP glaciers. Analysis further reveals that MPs in glaciers are associated with atmospheric mineral dust deposition. This study provides new data for the investigation of MPs in glaciers of remote areas, and a reference for studying MPs in the ice cores of TP glaciers.

Atmospheric deposition of microplastics in an urban conglomerate near to the foothills of Indian Himalayas: Investigating the quantity, chemical character, possible sources and transport mechanisms

The global apprehension regarding the ubiquitous presence of microplastics (MPs) and their associated health risks underscore a significant challenge. However, our understanding on the occurrence and characteristics of this emerging class of pollutants in the different environmental compartments remains limited. For instance, despite housing approximately 20-25% of the global population, the evidence of the atmospheric MPs in Indian Subcontinent is exceedingly rare. Hence, we for the first-time present data on the depositional flux, chemical composition, morphological features of the atmospheric MPs collected from the foothills of Indian Himalayas. The total number of MPs for the collected samples ranged from 65 to 752 particles, with an average of 317 ± 171 particles count. The average flux of atmospheric MPs was 2256 ± 1221 particles/m2/day and varied significantly from 462 particles/m2/day to 5346 particles/m2/day. The highest deposition (5346 particles/m2/day) of atmospheric MPs was recorded during the 3rd week of sampling, coinciding with the Diwali festival. Based on the visual characteristics, we determined that the size of MPs ranged from 67 to 2320 μm, with a predominant presence of smaller particles (<1200 μm), primarily composed of fragments and films/sheets. Raman spectroscopy indicated that the analyzed MPs were mainly composed of 4 different polymer types, including PE (46.8 ± 7.2 %), PP (20.9 ± 7.4 %), PS (15.6 ± 3.8 %) and PET (16.7 ± 9.9 %). We further highlighted the extent to which climate variables control the deposition of atmospheric MPs in this urban conglomerate located in the foothills of Himalayas. Our Lagrangian parcel tracking approach showed that the greater frequencies are of local origin and clustered near to the studied region. We also speculate that atmospheric microplastics can be transported along the westerly winds. Though we did not observe any significant relation (p > 0.05) between meteorological parameters and the quantity of atmospheric MPs.

Phosphorus recovery via struvite crystallization in batch and fluidized-bed reactors: Roles of microplastics and dissolved organic matter

Struvite crystallization, a promising technology for nutrient recovery from wastewater, is facing considerable challenges due to the presence of emerging contaminants such as microplastics (MPs) ubiquitously found in wastewater. Here, we investigate the roles of MPs and humic acid (HA) in struvite crystallization in batch and fluidized-bed reactors (FBRs) using synthetic and real wastewater with a Mg:N:P molar ratio of 1:3:(1-1.3) at an initial pH of 11. Batch reactor (BR) experiment results show that MPs expedited the nucleation and growth rates of struvite (e.g., the rate of crystal growth in the presence of 30 mg L-1 of polyethylene terephthalate (PET) was 1.43 times higher than that in the blank system), while HA hindered the formation of struvite. X-ray diffraction and the Rietveld refinement analysis revealed that the presence of MPs and HA can result in significant changes in phase compositions of the reclaimed precipitates, with over 80 % purity of struvite found in the precipitates from suspensions in the presence of 30 mg L-1 of MPs. Further characterizations demonstrated that MPs act as seeds of struvite nucleation, spurring the formation of well-defined struvite, while HA favors the formation of newberyite rather than struvite in both reactors. These findings highlight the need for a more comprehensive understanding of the interactions between emerging contaminants and struvite crystallization processes to optimize nutrient recovery strategies for mitigating their adverse impact on the quality and yield of struvite-based fertilizers. ENVIRONMENTAL IMPLICATION: The presence of microplastics in wastewater poses a significant challenge to struvite crystallization for nutrient recovery, as it accelerates nucleation and growth rates of struvite crystals. This can lead to changes in the phase compositions of the reclaimed precipitates, with implications for the quality and yield of struvite-based fertilizers. Additionally, the presence of humic acid hinders the formation of struvite, favoring the formation of other minerals like newberyite. Understanding the interactions between emerging contaminants and struvite crystallization processes is crucial for optimizing nutrient recovery strategies and mitigating the environmental impact of these contaminants on water quality and struvite-based fertilizers.

A simple model for predicting the hydraulic conductivity of MICP-treated sand

In this research paper, we introduce a novel and sustainable approach for forecasting the hydraulic conductivity of sand layers subjected to microbial-induced carbonate precipitation (MICP) to mitigate the diffusion of toxic pollutants. The proposed model uniquely integrates the impact of varying CaCO3 contents on the void ratio and estimates the average particle size of CaCO3 crystals through scanning electron microscopy (SEM) analysis. By incorporating these parameters into the K-C equation, a simplified predictive model is formulated for assessing the hydraulic conductivity of MICP-treated sand layers. The model's effectiveness is validated through comparison with experimental data and alternative models. The outcomes demonstrate a substantial reduction in hydraulic conductivity, with a decrease ranging between 93 and 97% in the initial assessment and a decrease between 67 and 92% in the follow-up assessment, both at 10% CaCO3 content. Notably, the hydraulic conductivity shows an initial sharp decrease followed by stabilization. These findings provide valuable insights into improving the prediction of hydraulic conductivity in MICP-treated sand layers, promoting a sustainable method for preventing pollution dispersion.

Probabilistic Estimation of Airborne Micro- and Nanoplastic Intake in Humans

Little research exists on the magnitude, variability, and uncertainty of human exposure to airborne micro- and nanoplastics (AMNPs), despite their critical role in human exposure to MNPs. We probabilistically estimate the global intake of AMNPs through three main pathways: indoor inhalation, outdoor inhalation, and ingestion during indoor meals, for both children and adults. The median inhalation of AMPs is 1,207.7 (90% CI, 42.5-8.48 × 104) and 1,354.7 (90% CI, 47.4-9.55 × 104) N/capita/day for children and adults, respectively. The annual intake of AMPs is 13.18 mg/capita/a for children and 19.10 mg/capita/a for adults, which is approximately one-fifth and one-third of the mass of a standard stamp, assuming a consistent daily intake of medians. The majority of AMP number intake occurs through inhalation, while the ingestion of deposited AMPs during meals contributes the most in terms of mass. Furthermore, the median ANP intake through outdoor inhalation is 9,638.1 N/day (8.23 × 10-6 μg/d) and 5,410.6 N/day (4.62 × 10-6 μg/d) for children and adults, respectively, compared to 5.30 × 105 N/day (5.79 × 10-4 μg/d) and 6.00 × 105 N/day (6.55 × 10-4 μg/d) via indoor inhalation. Considering the increased toxicity of smaller MNPs, the significant number of ANPs inhaled warrants great attention. Collaborative efforts are imperative to further elucidate and combat the current MPN risks.

Systematic review of microplastics and nanoplastics in indoor and outdoor air: identifying a framework and data needs for quantifying human inhalation exposures

BACKGROUND

Humans are likely exposed to microplastics (MPs) in a variety of places including indoor and outdoor air. Research to better understand how exposure to MPs correlates to health is growing. To fully understand the possible impacts of MPs on human health, it is necessary to quantify MP exposure and identify what critical data gaps exist.

OBJECTIVES

The current paper provides a human exposure assessment of microplastics in the air using systematically reviewed literature that provided concentration of MPs in air as well as doses used in toxicology studies to calculate inhalation exposure dose.

METHODS

All published peer-reviewed journal articles, non-published papers, and grey literature that focused on micro- or nano-plastics in indoor and outdoor air were systematically searched using PRISMA guidelines. Literature that defined specific concentrations and size of MPs in air or exposed to human lung cells, animals, or humans with measurable health impacts were included in data extraction. Inhalational exposures were calculated for different age groups using published MP concentrations from the included literature using exposure dose equations and values from U.S. ATSDR and EPA.

RESULTS

Calculated mean indoor inhalational exposures from passive sampling methods were higher than those calculated from active sampling methods. When comparing indoor and outdoor sampling, calculated inhalation exposures from indoor samples were greater than those from outdoor samples. Inhalation exposures of MPs differed between age groups with infants having the highest calculated dose values for all locations followed by preschool age children, middle-school aged children, pregnant women, adolescents, and non-pregnant adults. MP doses used in toxicology studies produced higher calculated mean inhalational exposures than those from environmental samples.

IMPACT

This study is the first known systematic review of inhalational MP exposure from indoor and outdoor air. It also provides inhalational exposures calculated from previously published environmental samples of MPs as well as from toxicology studies.

Atmospheric microplastic deposition in a coastal city of India: The influence of a landfill source on monsoon winds

Coastal zones experience various wind events that may influence the characteristics, distribution, and dynamics of atmospheric microplastic pollutants. In the present study, we investigated the characteristics of the bulk atmospheric microplastic deposition in Kochi, Kerala, India, during three distinct seasons: Northeast Monsoon (NEM), Summer (SMR), and Southwest monsoon (SWM). Seasonally, the highest microplastic fallout rate was recorded for the NEM (37.29 particles m-2d-1), followed by SMR (15.17 particles m-2 d-1) and the SWM (11.57 particles m-2d-1). The microplastic abundance was not correlated to the amount of rainfall. Further, the wind rose and HYSPLIT trajectory analysis illustrated the arrival of northeast monsoon winds to the city via the region in and around the municipal landfill, which could be a major source of airborne microplastic to the sampling stations, and the forward trajectories from the landfill site extended into the Arabia Sea, providing evidence on the potential atmospheric transport and subsequent deposition of microplastics into the ocean. With respect to the qualitative characteristics, blue-coloured and fibrous microplastics dominated the samples with a considerable number of particles belonging to the size range of 200-500 μm. The practice of drying synthetic clothes under natural sunlight may have substantially contributed to the increased prevalence of airborne microfibers. The higher numbers of polyethylene (PE) and polypropylene (PP) in the bulk microplastic deposition reinforce the concept of low-density polymers being more susceptible to deflation by the wind. Overall, the work signifies the role of monsoon winds in transporting microplastics from an unscientifically managed municipal landfill site and also highlights the importance of reducing the quantity of plastic waste ending up at the landfill to reduce the emission of microplastics proportionately.

Microplastics in waste management systems: A review of analytical methods, challenges and prospects

Numerous studies have reported the presence of microplastics (MPs) in waste collection and disposal systems. However, current scientific studies on measuring MP occurrence in a waste management context are not comparable due to a lack of standardized methodologies. Consequently, the impact of MPs on ecosystems and human health remains largely unclear. To address the inconsistencies, present in published studies, this review thoroughly examines sample preparation techniques for transfer stations, landfill leachate, recycling, compost, and incineration ash samples. Furthermore, various analytical approaches such as flotation, filtration, and organic matter digestion, as well as morphological categorization, identification, and quantification, are subsequently rigorously assessed. The benefits and limitations of each methodology are evaluated to facilitate the development of accurate and effective methods for detecting and characterizing nanoplastics. Recent research suggests that plastic recycling and composting facilities are the primary environmental sources of microplastic pollution among different waste treatment methods. The most prevalent microplastic types discovered in waste management were polyethylene (PE) and polypropylene (PP), with fragment and fiber being the most frequently reported morphologies. The review highlights a number of tactics that could be integrated into the methodology development for detecting microplastics in waste management systems (WMS), ultimately leading to better consistency and reliability of data across different studies. In essence, this will advance our comprehension of potential risks associated with microplastics.

Characterization of airborne microplastics at different workplaces of the poly(ethylene:propylene:diene) (EPDM) rubber industry

Microplastics (MPs) as an emerging air pollutant have received widespread attention, but research on airborne MPs at occupational sites is still limited, especially in the rubber industry. Hence, indoor air samples were collected from three production workshops and an office of a rubber factory producing automotive parts to analyze the characteristics of airborne MPs in different workplaces of this industry. We found MP contamination in all air samples from the rubber industry, and the airborne MPs at all sites mainly showed small-sized (< 100 μm) and fragmented characteristics. The abundance and source of MPs at various locations is primarily related to the manufacturing process and raw materials of the workshop. The abundance of MPs in the air was higher in workplaces where production activities are involved than in office (360 ± 61 n/m³), of which the highest abundance of airborne MPs was in the post-processing workshop (559 ± 184 n/m³). In terms of types, a total of 40 polymer types were identified. The post-processing workshop has the largest proportion of injection-molded plastic ABS, the extrusion workshop has a greater proportion of EPDM rubber than the other locations, and the refining workshop has more MPs used as adhesives, such as aromatic hydrocarbon resin (AHCR).

Treatment of compressed leachate from refuse transfer stations by freeze-melt method

A small amount of leachate with complex composition will be produced during the compressing of municipal solid waste in refuse transfer stations. In this study, the freeze-melt method, a green and efficient wastewater treatment technology, was used to treat the compressed leachate. The effects of freezing temperature, freezing duration, and ice melting method on the removal rates of contaminants were investigated. The results showed that the freeze-melt method was not selective for the removal of chemical oxygen demand (COD), total organic carbon (TOC), ammonia-nitrogen (NH₃-N) and total phosphorus (TP). The removal rate of contaminants was positively correlated with freezing temperature and negatively correlated with freezing duration, and the slower the growth rate of ice, the higher the purity of ice. When the compressed leachate was frozen at -15 °C for 42 h, the removal rates of COD, TOC, NH₃-N and TP were 60.00%, 58.40%, 56.89% and 55.34%, respectively. Contaminants trapped in ice were removed during the melting process, especially in the early stages of melting. The divided melting method was more beneficial than the natural melting method in removing contaminants during the initial stage of melting, which contributes to the reduction of produced water losses. This study provides a new idea for the treatment of small amounts of highly concentrated leachate generated by compression facilities distributed in various corners of the city.

There's something in the air: A review of sources, prevalence and behaviour of microplastics in the atmosphere

Literature regarding microplastics in the atmosphere has advanced in recent years. However, studies have been undertaken in isolation with minimal collaboration and exploration of the relationships between air, deposition and dust. This review collates concentrations (particle count and mass-based), shape, size and polymetric characteristics for microplastics in ambient air (m3), deposition (m2/day), dust (microplastics/g) and snow (microplastics/L) from 124 peer-reviewed articles to provide a holistic overview and analysis of our current knowledge. In summary, ambient air featured concentrations between <1 to >1000 microplastics/m³ (outdoor) and <1 microplastic/m³ to 1583 ± 1181 (mean) microplastics/m³ (indoor), consisting of polyethylene terephthalate, polyethylene, polypropylene. No difference (p > 0.05) was observed between indoor and outdoor concentrations or the minimum size of microplastics (p > 0.5). Maximum microplastic sizes were larger indoors (p < 0.05). Deposition concentrations ranged between 0.5 and 1357 microplastics/m²/day (outdoor) and 475 to 19,600 microplastics/m²/day (indoor), including polyethylene, polystyrene, polypropylene, polyethylene terephthalate. Concentrations varied between indoor and outdoor deposition (p < 0.05), being more abundant indoors, potentially closer to sources/sinks. No difference was observed between the minimum or maximum reported microplastic sizes within indoor and outdoor deposition (p > 0.05). Road dust concentrations varied between 2 ± 2 and 477 microplastics/g (mean), consisting of polyvinyl chloride, polyethylene, polypropylene. Mean outdoor dust concentrations ranged from <1 microplastic/g (remote desert) to between 18 and 225 microplastics/g, comprised of polyethylene terephthalate, polyamide, polypropylene. Snow concentrations varied between 0.1 and 30,000 microplastics/L, containing polyethylene, polyamide, polypropylene. Concentrations within indoor dust varied between 10 and 67,000 microplastics/g, including polyethylene terephthalate, polyethylene, polypropylene. No difference was observed between indoor and outdoor concentrations (microplastics/g) or maximum size (p > 0.05). The minimum size of microplastics were smaller within outdoor dust (p > 0.05). Although comparability is hindered by differing sampling methods, analytical techniques, polymers investigated, spectral libraries and inconsistent terminology, this review provides a synopsis of knowledge to date regarding atmospheric microplastics.

Atmospheric microplastics: exposure, toxicity, and detrimental health effects

Microplastics (MPs) are micro-particulate pollutants present in all environments whose ubiquity leads humans to unavoidable exposure. Due to low density, MPs also accumulate in the atmosphere, where they are easily transported worldwide and come into direct contact with the human body by inhalation or ingestion, causing detrimental health effects. This literature review presents the sources of atmospheric MPs pollution, transport routes, physicochemical characteristics, and environmental interactions. The document also explains the implications for human health and analyzes the risk of exposure based on the potential toxicity and the concentration in the atmosphere. MPs' toxicity lies in their physical characteristics, chemical composition, environmental interactions, and degree of aging. The abundance and concentration of these microparticles are associated with nearby production sources and their displacement in the atmosphere. The above elements are presented in an integrated way to facilitate a better understanding of the associated risk. The investigation results encourage the development of future research that delves into the health implications of exposure to airborne MPs and raises awareness of the risks of current plastic pollution to promote the establishment of relevant mitigation policies and procedures.

Airborne microplastics: Occurrence, sources, fate, risks and mitigation

This paper serves to enhance the current knowledge base of airborne microplastics which is significantly smaller than that of microplastics in marine, freshwater and terrestrial environments. It systematically presents the prevalence, sources, fate, risks and mitigations of airborne microplastics through the review of >140 scientific papers published mainly in the last 10 years. Unlike the extant review, it places an emphasis on the indoor microplastics, the risks of airborne microplastics on animals and plants and their mitigations. The outdoor microplastics are mostly generated by the wear and tear of tires, brake pads, waste incineration and industrial activities. They have been detected in many regions worldwide at concentrations ranging from 0.3 particles/m³ to 154,000 particles/L of air even in the Pyrenees Mountains and the Arctic. As for indoor microplastics, the reported concentrations range from 1 piece/m³ to 9900 pieces/m²/day, and are frequently higher than those of the outdoor microplastics. They come from the wear and tear of walls and ceilings, synthetic textiles and furniture finishings. Airborne microplastics could be suspended and resuspended, entrapped, settle under gravity as well as interact with chemicals, microorganisms and other microplastic particles. In the outdoors, they could also interact with sunlight and be carried by the wind over long distance. Airborne microplastics could adversely affect plants, animals and humans, leading to reduced photosynthetic rate, retarded growth, oxidative stress, inflammatory responses and increased cancer risks in humans. They could be mitigated indirectly through filters attached to air-conditioning system and directly through source reduction, regulation and biodegradable substitutes.

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.

A novel application of thermogravimetry-mass spectrometry for polystyrene quantification in the PM10 and PM2.5 fractions of airborne microplastics

Microplastics have appeared as emerging pollutants due to the diverse applications of plastics in today's world. Growing evidence points to the negative impacts that airborne microplastics have on human health, as they can enter the human body through respiration. Our aim was to quantify polystyrene airborne microplastics in smaller fractions, thoracic (PM₁₀) and alveolar (PM_2.5), as they have scarcely been studied. In this work, we proposed a methodology based on thermogravimetric analysis coupled with mass spectrometry that requires minimal sample preparation and does not limit particle size. We applied this methodology to quantify the airborne polystyrene in PM₁₀ and PM_2.5 fractions in mass units of microplastics per m³ of air in an urban and agricultural region during the summer of 2021. The mean concentrations of polystyrene found in the PM₁₀ and PM_2.5 fractions were 2.09 and 1.81 ng m^-3, respectively. Therefore, the majority of airborne polystyrene microplastics are found in the alveolar fraction which, is associated with severe cardiopulmonary and respiratory diseases. According to air mass backward trajectories, it was noted that the main sources of these emerging pollutants could be related to local agricultural practices.

Occurrence and characteristics of atmospheric microplastics in Mexico City

While atmospheric microplastics have attracted scientific attention as a significant source of microplastic contamination in the environment, studies in large population centers remain sparse. Here we present the first report on the occurrence and distribution of atmospheric microplastics in Mexico City (Latin America's second most densely populated city), collected using PM₁₀ and PM_2.5 active samplers at seven monitoring stations (urban, residential, and industrial) during the dry and wet seasons of 2020. The results showed that microplastics were detected in all of the samples examined, with mean microplastic concentrations (items m^-3) of 0.205 ± 0.061 and 0.110 ± 0.055 in PM₁₀ and PM_2.5, respectively. The spatial distribution of microplastics showed seasonal variation, with greater abundances in locations closer to industrial and urban centers. There was also a significant difference in microplastic concentrations in PM₁₀ and PM_2.5 between the dry and wet seasons. The mean PM_2.5/PM₁₀ ratio was 0.576, implying that microplastics were partitioned more towards PM_2.5 than PM₁₀ in Mexico City. Fibers were the most prominent shape (>75 %), and blue was the most common color (>60 %). The size characteristics indicated microplastics of varying lengths, ranging from 39 to 5000 μm, with 66 % being <500 μm. Metal contaminants such as aluminum, iron, and titanium were detected using SEM-EDX on randomly selected microplastics. The microplastics were identified as cellophane, polyethylene, polyethylene terephthalate, polyamide, and cellulose (rayon) using ATR-FTIR spectral analysis. Our findings unravel the extent and characteristics of atmospheric microplastics in the Mexico City metropolitan area, which will aid future research to better understand their fate, transport, and potential health risks, demanding more investigations and close monitoring.