Microplastic Cycle in the Environment

Abstract

Microplastics have become a pervasive environmental threat, contaminating marine, freshwater, soil, and atmospheric environments. The issue is that, although considerable research has been conducted on soil, marine, and freshwater pollution, the pathways and interconnectedness of microplastic movement between ecosystems and the mechanisms driving this movement have not been thoroughly detailed. This has led to an incomplete understanding of the complex and imperfect cycle formed as microplastics circulate through the environment, despite some research addressing their transport. Understanding the sources, transport mechanisms, and environmental and health impacts of microplastics is essential for developing effective strategies to reduce their release into the environment. This review delves into global plastic and microplastic production, consumption, and pathways, examining their occurrence, transport, raw polymer composition, additives, toxicity, and the cyclical nature of microplastic contamination across ecosystems. By thoroughly reviewing existing literature, this analysis aims to comprehensively understand the incomplete and complex circulation of microplastics in the environment along with their impacts on the environment and human health.

Keywords: Plastics, Microplastics, Microbeads, Biological process, Chemical process.

Introduction

Microplastic increase in the environment is one of the most pressing environmental issues in this 21st century. Microplastics are fragments of any plastic less than 5 mm (0.20 in) in length¹. Due to their persistence and potential adverse effects on ecosystems and human health, microplastics pose a threat and continue to be a global issue to deal with. Through anthropogenic activities such as the breakdown of larger plastic debris, industrial processes, the abrasion of synthetic textiles and tile, and many more, microplastics are released that contaminate marine, freshwater, terrestrial, and atmospheric environments. Microplastics can penetrate the most pristine and isolated regions of the world as they are being discharged into the environment, traveling greater distances through agents or carries, and are deposited into these remote areas²,³,⁴. According to recent research, certain microplastic particles may be re-emitted into the atmosphere, casting doubt on the notion that plastics that reach the ocean stay restricted to the marine ecosystem. Microplastics can be carried into the atmosphere from the ocean surface by processes such as bubble burst ejection and wave action, which are fueled by wind and sea state turbulence. The global cycle of microplastic pollution is further exacerbated by the land-based transportation of these airborne particles⁵,⁶,⁷. The amount of plastic produced worldwide has increased exponentially, from 2 million metric tons in 1950 to 280 million tons in 2016. The great majority of plastic products (79%) are thrown out into the environment, where they can break down and become smaller-sized litter⁸,⁹,¹⁰,¹¹. Microplastics (MPs) have been found in a variety of environments, including freshwater¹², benthic sediment¹³, soil¹⁴, atmospheres, seawater¹⁵, beach sand¹⁶, and even far-flung places like the polar regions¹⁷ and the Tibet Plateau¹⁸. Additionally, MPs can be absorbed by a variety of terrestrial and aquatic creatures, including earthworms and snails, as well as plants¹⁹,²⁰. These organisms include fish and mussels²¹,²²,²³. Therefore, MPs merit careful consideration as they could have a large impact on the Earth’s environment. Although substantial research has been conducted on pollution in marine, freshwater, and soil systems, the pathways and interconnectedness of microplastic movement between these ecosystems and the mechanisms driving this movement have not been thoroughly detailed. This neglect indicates a serious knowledge gap about the extent of microplastic contamination and its effects on the ecosystem and public health²⁴,²⁵. A thorough understanding of microplastics’ sources, transport processes, and environmental effects is crucial due to the intricate and linked paths of their dissemination. The objective of this study is to clarify the current status of our understanding of microplastic contamination, with a particular emphasis on its transport and circulation between freshwater, marine, terrestrial, and atmospheric systems. We will also examine the kinds and sources of microplastics, their effects on the environment and human health (Table 1), and possible paths of microplastic transport (Fig. 1)²⁶,²⁷.  This review seeks to address this gap by examining global plastic and microplastic production, consumption, and pathways, focusing on their occurrence, transport, raw polymer composition, additives, toxicity, and the cyclical nature of microplastic contamination across different ecosystems. Through a comprehensive review of existing literature, this analysis aims to provide a detailed understanding of the incomplete and complex circulation of microplastics in the environment.

Types, Occurrences, and Sources of Microplastics.

The term “microplastics” is used to differentiate smaller or minute plastics from larger plastic waste, such as plastic bottles or bigger pieces of plastic. Two classifications of microplastics are currently recognized: primary and secondary. Primary microplastics are deliberately produced to be small, such as microbeads used in cosmetics and personal care products, while secondary microplastics result from the breakdown of larger plastic items. Secondary microplastics are the most common type found in the environment²⁸. Primary microplastics include any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment¹. These include microfibers from clothing, microbeads, plastic glitter²⁹, and plastic pellets (also known as nurdles)³⁰,³¹. Secondary microplastics arise from the degradation of larger plastic products through natural weathering processes after entering the environment¹. Both types are known to persist in the environment at high levels, particularly in aquatic and marine ecosystems, where they cause water pollution. Thirty-five percent of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester, acrylic, or nylon-based clothing, often during the washing process³². Microplastics (MP) are categorized by their morphology, including size and shape, using the standardized size and color sorting (SCS) system. This categorization aims to standardize and facilitate the comparison of study results worldwide. Shapes, colors, and texture are used to determine whether a suspected item is an MP³³. MPs vary in shape from irregular to spherical and long-thin fibers. Plastic pellets present tablet-like, oblong, cylindrical, spherical, and disk shapes, mostly spherical to oval with rounded ends³⁴. One of the most common sources of microplastics is discarded plastic products, such as bags, bottles, and packaging materials. When these plastics break down, they release small particles that can end up in the soil and water. Additionally, microplastics can also come from synthetic fibers in clothing that are shed during washing and drying processes³⁵. Primary sources include household sewage discharge, polymeric particles from cosmetic and cleaning products, feedstocks used to manufacture plastic products, and plastic pellets or powders used for air blasting³⁶. Progressive fragmentation of larger plastic items under atmospheric conditions, e.g., by mechanical degradation and UV light exposure, contributes to the entrance of significant amounts of microplastics into the environment³⁷. This increases plastic debris availability for ingestion by various organisms, highlighting the emergence of further environmental hazards³⁸. Wastewater treatment plants are also a major source of microplastic release³⁹,⁴⁰. While large plastic particles are efficiently removed during wastewater treatment, microplastics often bypass the treatment units, entering and accumulating in the aquatic environment⁴¹. Notably, many water treatment plants are located near the ocean and seawater, thus becoming a significant source of microplastic release. For instance, in mainland China, about 1,873 wastewater plants (56%) out of 3,340, with a treatment capacity of 78×10⁶ m³/day, are located in coastal regions where their effects can be directly or indirectly discharged into aquatic ecosystems⁴². Additionally, MP fibers can be produced due to mechanical wear or damage to textile clothing and bedding, including pillows, blankets, and curtains. In the sun, photooxidation and thermal effects of drying clothes can easily promote the decomposition and degradation of these textiles, causing the release of microfibers⁴³. These fibrous MPs can then be broken into smaller-sized fine items through wind shear or wear and other environmental factors⁴⁴. The sources of microplastics, the kinds of microplastics they produce, and the release of these microplastics into the environment are all displayed in the table below(Table. I).⁴⁵

Sources	Types of Microplastic Present	Occurrence, generation, and release into the environment
Textiles	Polyester, Nylon, Acrylic Polyethylene, Polyurethane	Microfibers are released from natural fabrics like cotton and wool and synthetic materials like polyester, nylon, and acrylic when they are used or washed. These fibers are washed ashore in rivers and seas, where they are eaten by marine organisms like fish. Because they are used so extensively in the textile industry, microfibers are the most prevalent type of microplastics discovered in marine environments.
Paints and finishes	Acrylic, Polyurethane, Polyvinyl chloride (PVC), Polystyrene, Polyethylene, Polypropylene	Microplastics included in most paints and finishes have the potential to leak into the environment when applied or removed. These particles have the potential to affect neighboring ecosystems and human health since they are inhaled through respiration and can wind up in the air, streams, or soil.
Industrial Processes	Polyethylene (PE), Polypropylene (PP), Polyvinyl chloride (PVC), Polyethylene terephthalate (PET), Polystyrene (PS), Nylon, Acrylic polymers	Microplastics are produced as waste products during manufacturing processes like the fabrication of plastic or the cutting and grinding of plastic materials, and they are then released into the air or waterbodies close to industrial sites. This results in a detrimental influence on our ecosystems and human health.
Cosmetics and personal care products	Polyethylene (PE) Polypropylene (PP) Nylon Polyethylene terephthalate (PET) Polymethyl methacrylate (PMMA) Polyurethane (PU)	Microbeads and other microplastics are frequently utilized as abrasives or exfoliants in body wash, toothpaste, and face scrubs. These tiny particles wind up in waterways and seas because they are little items that simply get filtered out by wastewater treatment plants and other modern methods.
Plastic packaging, containers, and Tire wear	Polyethylene (PE) Polypropylene (PP) Polyethylene terephthalate (PET) Polystyrene (PS) Polyvinyl chloride (PVC) Nylon Acrylic polymers	Due to exposure to sunlight and other environmental variables, single-use plastics such as food containers, water bottles, and plastic bags have the potential to fragment into smaller pieces over time. Eventually, these smaller fragments may turn into difficult-to-remove microplastics from the environment. Road wear causes tires to emit microscopic rubber fragments, some of which may include microplastics. These particles can potentially affect the environment and public health if they wash into streams or become airborne.

Transport Mechanisms of Microplastics

Sea and ocean are viewed as microplastic sinks, whereas freshwaters and terrestrial environments are the main sources. Indeed, early research found that microplastic litter reaching oceans by rivers contains particles found in soils⁴⁶. This implies that freshwaters and soils are also sinks of microplastics, as evidenced by high concentrations in some terrestrial and freshwater areas⁴⁷. This shows that there is transport of microplastics from one ecosystem to another through various media and mechanisms(Fig.1). In this section, we will review the various mechanisms for the transport of microplastics from one ecosystem to another and their harmful impact.

Transport of Microplastics from Terrestrial ecosystem into Aquatic ecosystem:

There are various mechanisms by which microplastics move from the land into water bodies. These include the following:

1. Flooding and Erosions: Flooding events, influenced by factors like excessive rainfall, artificial irrigation, and increased flow rates, significantly expedite the transport of microplastics (MPs) from land into water bodies. These events increase flow velocities in rivers and streams, dislodging and transporting accumulated microplastics from terrestrial sources such as littered areas, agricultural fields with plastic mulches, and urban environments with plastic debris. The higher volume of water during flooding mobilizes larger quantities of microplastics that have settled on land, which are then carried into nearby water bodies through runoff. Erosion of river banks and beds during floods further contributes to this transport by releasing microplastics adsorbed to soil particles and sediment into aquatic ecosystems. Artificial irrigation in agriculture also plays a role, causing localized flooding or runoff that can transport microplastics from soils, particularly those contaminated by plastic agricultural materials⁴⁸.
2. Landfill Leachate: Microplastics (MPs) are transported from landfills into water bodies through landfill leachate, which often contains dissolved and suspended microplastics from degraded plastic waste. These MPs originate from various sources within the landfill, including solid waste and wastewater treatment plant residuals such as sludge and fat, oil, and grease⁴⁹. Plastic waste in landfills undergoes abrasive activities, breaking down into secondary microplastics, while MPs also enter from primary sources, such as products directly disposed of in the landfill. Wastewater, a significant collection point for MPs, contributes to this process, as MPs can become entrapped in fat, oil, grease, and solid sludge during treatment. Upon disposal in landfills, these materials increase the abundance of MPs in landfill leachate, which can seep into groundwater and surface water bodies, transporting MPs from the landfill into these water bodies²⁵,⁵⁰.
3. Wind Transport: In coastal and marine environments, wind can carry lightweight microplastics from beaches, roadsides, or other exposed surfaces and deposit them directly into water bodies. Although there isn’t enough data to support the transport of microplastics into these waterbodies, direct observations and research studies reinforce it.
4. Sewage and Wastewater Discharge: Microplastics (MPs) are transported from land into water bodies primarily through sewage and wastewater discharge. Wastewater treatment plants (WWTPs) often fail to filter out all small plastic particles, allowing MPs to enter water bodies through their effluents. Additionally, untreated sewage discharges can directly release MPs into rivers and oceans. Major sources of MPs include personal care products, cleansing agents, synthetic discharge, air blast media, industrial raw materials, and poor waste management systems⁵¹,⁵². WWTPs receive MPs from various domestic and industrial sources, including textiles, city dust, tire shedding, plastic pellet fragments, road paint, and other plastic-based items. These MPs are drained through wastewater during washing processes and eventually make their way to WWTPs⁵³. Once in the WWTPs, these MPs can pass through treatment processes and be discharged into water bodies, further contributing to the pollution of rivers, oceans, and other surface waters.
5. Direct Deposition: Ocean-based sources of marine litter include materials lost or discarded from various activities such as fishing vessels, aquaculture facilities, merchant ships, recreational boats, offshore oil or gas platforms, and military operations. Cargo loss from merchant ships can significantly contribute to plastic pollution in the marine environment²⁴,⁵⁴,⁵⁵,⁵⁶. Although the dumping of plastic waste at sea has been prohibited since 1988, evidence suggests that a substantial number of vessels continue to illegally dispose of plastic waste into the ocean, resulting in the increase of microplastic pollution in oceans and other waterbodies⁵⁷,⁵⁸.

Transport of Microplastics from Terrestrial ecosystems into the Atmosphere:

There are various mechanisms by which microplastics move from the land into the Atmosphere. These include the following:

• Wind Erosion: Microplastics (MPs) are transported from land into the atmosphere through various mechanisms, primarily driven by wind erosion. The textile industry is a major contributor to atmospheric MP pollution, with synthetic fibers such as polyester, polyolefin, nylon, polyurethane, polymethyl methacrylate, and vinyl being key sources⁵⁹. Manufacturing processes, including cutting, grinding, and weaving, generate a substantial number of these microscale synthetic fibers, which can be carried into the atmosphere by wind. Wind action also facilitates the movement of synthetic polymer particles and enriches wind-eroded sediments with MPs. Secondary MPs originate from the breakdown of larger plastics due to weathering, UV exposure, and physical, chemical, or biological degradation⁶⁰,⁶¹. Significant sources of secondary MPs include micro-rubbers from tire wear and tear, as well as microfibers released during the wearing, washing, and drying of clothes(Sun et al., 2022). Despite synthetic rubber containing polymers, the classification of micro-rubbers as natural or synthetic remains debatable due to the presence of both natural and synthetic components in tires.
• Industrial Processes: Microplastics (MPs) are transported from land into the atmosphere through various industrial processes, including the intentional manufacture of micro-sized plastics. For example, polyvinyl chloride (PVC) resin is often produced and supplied as a fine powder due to its enhanced resistance to degradation and oxidation⁶². These powder forms are susceptible to becoming airborne during the processing stages. Additionally, during thermoplastic polymer molding processes, polymers are ground into powder form (150-500 μm) to achieve higher-quality polymer molds⁶³. This molding process can release polymer powder into the atmosphere, thereby contributing to atmospheric MP pollution.

• Transpiration: Microplastics in fertilizers and on the land surface can sink into the soil. Animals can transport and disperse these microplastics through external attachment or by ingestion and subsequent defecation⁶⁴,⁶⁵. Once microplastics enter plant roots, they are transported from the roots to the shoots, with the uptake rate predominantly determined by the plant’s transpirational pull; higher transpiration rates lead to greater uptake (Li et al., 2020). This process results in the transportation of microplastics along with water vapor through transpiration (the evaporation of water from plant leaves) into the atmosphere.

• Burning of plastics: Microplastics (MPs) are significantly transported from land into the atmosphere through the open burning of plastic waste, a widespread practice in many regions. This burning process releases MPs directly into the air, accompanied by a variety of other pollutants. In open landfills, substantial quantities of plastics are incinerated daily, causing the volatilization of numerous harmful compounds that integrate into atmospheric aerosols⁶⁶,⁶⁷. The release of MPs and toxic chemicals during burning not only contaminates the immediate environment but also allows MPs to travel vast distances through air currents, exacerbating global pollution. This highlights the critical need for improved waste management practices to mitigate the pervasive spread of MPs and protect atmospheric quality.

Transport of Microplastics From Aquatic Ecosystems into Both the Terrestrial Ecosystem and the Atmosphere:

Microplastics are transported from the atmosphere to both water bodies and land through various mechanisms. These include the following:

1. Sea Spray: The oceans have been investigated as possible sources of atmospheric MPs. Allen et al. (2020) conducted a groundbreaking study that suggested that MPs from the sea could enter the atmosphere through sea spray aerosols produced by wave breaking at the water’s surface⁶⁸,⁶⁹. This process involves the airborne release of tiny aerosol particles from bursting bubbles during wave breaking, driven by convective updraft. When the voids left by the bursting bubbles are filled by rushing water, secondary ejection takes place, expelling particles at a larger microscale. In situ studies have confirmed that MPs from the sea can become airborne through these mechanisms⁷⁰. Since most plastic particles have lower densities than ocean water, sea spray, and winds can likely cause MPs from rivers and lakes to become airborne in oceanic air. Sea sprays are formed during wave breaking in the coastal surf zone and through white cap formation caused by wind stress.
2. Meteorological Event: Atmospheric microplastics (MPs) are considered part of particulate matter (PM) and share several similarities with PM. Both primarily enter the atmosphere through strong wind flow processes, travel horizontally with air mass movement, and undergo deposition influenced by gravity and precipitation⁷¹. Meteorological conditions such as precipitation, air temperature, atmospheric pressure, humidity, wind velocity and direction, and atmospheric stability class can significantly influence the transport of atmospheric MPs. Irregular meteorological events like typhoons and storms can also alter regional airflow, affecting the transport of MPs⁷²,⁷³.
3. Surface impact: When raindrops hit the surface of lakes or oceans, they create numerous small droplets that are ejected into the atmosphere at high velocities. A recent study estimated that about 4,800 particles per square kilometer per hour can be propelled into the atmosphere through these droplets during a typical rainfall of 10 mm/h⁷⁴.
4. Food Web: The small size and slow biodegradation rate of microplastics (MPs) enable their absorption by various organisms, facilitating their transport through food webs and from oceans to land⁷⁵,⁷⁶. Marine organisms, from plankton to fish and larger animals, ingest MPs, which can then be carried across different habitats. Migrating fish and birds, for instance, can transfer MPs between oceanic and terrestrial environments. Additionally, when marine animals are caught and processed for human consumption, MPs in their guts and tissues enter terrestrial waste streams. Birds feeding in the ocean and nesting on land deposit MPs through their droppings, and sea turtles can introduce MPs to beaches during nesting. Thus, the persistence and small size of MPs allow them to be transported from oceans to land through diverse biological processes, highlighting the interconnectedness of marine and terrestrial ecosystems and the pervasive nature of plastic pollution.

Transport of Microplastics from the atmosphere into Both Aquatic and Terrestrial Ecosystems:

Microplastics in the atmosphere are transported and deposited on water bodies and land through various mechanisms. These include the following:

1. Precipitation: Microplastics (MPs) are transported from the atmosphere onto both land and water bodies primarily through atmospheric deposition, which is significantly driven by precipitation events such as rain and snow⁷⁷,⁷⁸. Wet deposition, including rainfall and snowfall, plays a crucial role in this process, effectively scouring atmospheric particles and depositing them in urban areas, seas, and even remote Arctic regions⁷⁸,⁷⁹. Snow, in particular, is an efficient method for depositing MPs, as it captures and deposits atmospheric particulates over large areas. A study by Bergmann et al. (2019) found that microplastic deposition ranged from 190 to 154,000 particles per liter in melted snow sampled from Europe and from 0 to 14,400 particles per liter in the Arctic. This demonstrates the pervasive nature of MP pollution and its ability to reach even the most remote and pristine environments.
2. Wet and dry deposition: Microplastics (MPs) and nanoplastics (NPs) have been shown to act as effective cloud ice nuclei, potentially explaining the correlation between MP deposition and snowfall events⁸⁰,⁷⁸. Snow effectively scrounges atmospheric MPs, contributing to the deposition of plastic particles in both urban and remote areas, such as the Arctic, as well as in global marine environments⁸¹. Suspended MPs are removed from the atmosphere through dry or wet deposition. Dry deposition occurs when gravitational forces on suspended MPs surpass wind flow forces⁸². Factors such as aging-induced cracks, void formation, and the adsorption of chemical or biological pollutants on MP surfaces can alter their specific gravity and buoyancy, triggering dry deposition⁸³. Thus, the surface state and degree of internal aging significantly influence the dry deposition process. Wet deposition involves MPs being washed out by precipitation, with rain droplets scavenging airborne MPs during rainfall and depositing them on surfaces. Mist and fog droplets can also interact with MPs before surface deposition⁸⁴,⁸⁵. For instance, atmospheric deposition of non-fibrous microplastics and fibers in Dongguan, China, ranged from 175 to 313 particles per square meter per day⁸⁶,⁸⁷.

The Impacts of the Transport of Microplastics between the various environmental Domains

The potential hazards of microplastics arise from the release of unreacted monomers, oligomers, and chemical additives over time. These monomers and oligomers can migrate from food packaging materials, and as their concentrations increase, the remaining particles can be absorbed by the human body through various pathways. Microplastics can impact the environment in multiple ways, including mechanical harm to organisms, serving as carriers for hydrophobic pollutants, and providing substrates for organisms⁸,⁸⁹. Below are some of the ways microplastics pose risks to both environmental and human health.

1. Entanglement: The transport of microplastics from land and atmospheric environments into oceans and aquatic ecosystems poses significant risks to marine life. These particles can entangle organisms, impairing their ability to feed and avoid predators, which may lead to exhaustion, starvation, or drowning (Fig.2)⁹⁰. While larger plastics can directly harm marine creatures through entanglement or ingestion, smaller microplastics can be absorbed through gills or ingested via the digestive system. For instance, in mussels, smaller microplastics are taken up through the gills via endocytosis, while larger particles are consumed. Air-breathing animals that become entangled in plastics may suffer severe injuries or death due to restricted movement and reduced food intake. Microplastics can cause similar physical damage, obstructing feeding and digestion, and injuring sensitive tissues such as gills or the intestinal tract. Even if immediate death does not occur, injuries and reduced foraging ability can critically impact an organism’s health and survival⁹¹,⁹².
2. Smothering: Microplastics transported from oceans and the atmosphere and deposited on land can profoundly affect ecosystems. In the intertidal zone, such debris can severely damage delicate salt marsh vegetation by either crushing plants or blocking essential light needed for their growth through its weight and shading, resulting in barren patches in these already sensitive environments⁹³. Furthermore, accumulating these materials can abrade or crush plant blades into anoxic sediments, potentially leading to the suffocation of plants, reduced photosynthetic activity, and eventual decay of above-ground biomass⁹⁴. These impacts highlight the potential for long-lasting damage to ecosystem function and biodiversity in these vulnerable habitats.
3. Vectors for pollutants: The transport of microplastics across various environmental domains—such as air, water, and soil—plays a critical role in the widespread dispersal of harmful pollutants. These tiny particles, characterized by their hydrophobic nature and large surface area, effectively adsorb and concentrate pollutants like hexachlorinated hexanes, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). As microplastics migrate through different environments, they act as vectors, carrying these toxic substances over long distances and into new ecosystems. This movement not only facilitates the spread of chemical contaminants but also increases the risk of environmental pollution and the exposure of organisms to toxic compounds⁹⁵,⁹⁶,⁹⁷,⁹⁸. Microplastics can interact with pollutants through hydrophobic, Van der Waals, and π-π interactions, further enhancing their ability to bind and transport these substances. The chemical composition of microplastics, along with their additives, determines their potential toxicity⁹⁹, which is amplified as they move between ecosystems, releasing both pathogens and chemical contaminants. Consequently, the mobility of microplastics across environmental domains exacerbates their environmental and health impacts by enabling the far-reaching distribution of hazardous pollutants.
4. Impacts on human health: The cycle of microplastics in the environment presents significant risks to human health through various pathways, notably ingestion, inhalation, and dermal exposure. When microplastics are released into the environment, they can enter the human body through contaminated food, air, and water. Ingestion is one of the most common pathways, as microplastics are present in seafood, drinking water, and even in food packaging and utensils. Once ingested, these particles can accumulate in the digestive tract and potentially translocate to other organs, leading to localized inflammation and possible genotoxic effects. Inhalation of microplastics is another critical concern, particularly for individuals exposed to airborne microplastics in industrial settings. Studies have documented the presence of fibrous microplastics in human lungs, with some fibers detected as large as 250 µm¹¹,¹⁰⁰. These particles can evade the body’s natural clearance mechanisms, persisting in the lungs and leading to reduced lung capacity, coughing, breathlessness, and inflammation¹⁰¹. Furthermore, fine microplastics have the potential to enter the circulatory system¹⁰², posing risks to other organs¹⁰³. Dermal exposure to microplastics can occur through personal care products containing microbeads, such as facial scrubs and body washes, as well as through synthetic clothing and textiles that shed microfibers. In addition to the physical presence of microplastics, the chemical additives, and dyes used in plastics, such as plasticizers and heavy metals like lead, can have toxic effects on humans¹⁰⁴,¹⁰⁵. Long-term exposure to these substances can result in severe health issues, including brain damage, muscle weakness, kidney failure, and even death¹⁰⁶. Moreover, microplastics serve as efficient substrates for the colonization of microorganisms, including pathogenic bacteria, viruses, protozoa, and fungi. These microorganisms can be transported by wind, water, and other environmental factors, further increasing the risk of infections and disease transmission. Overall, the cycle of microplastics in the environment not only contributes to widespread contamination but also poses a multifaceted threat to human health through various exposure routes, leading to both direct and indirect health impacts.

Methods

The literature review was conducted using databases like Google Scholar to ensure broad coverage of relevant studies. The search incorporated keywords such as “microplastics,” “environmental impact,” “pollutant transport,” and “ecotoxicology,” along with synonyms and related terms, to ensure a comprehensive exploration. The review focused on studies published between 2010 and 2023 to capture the most recent and relevant research. Only peer-reviewed studies in English that directly addressed the environmental impact of microplastics were included, while those published before 2010 or not directly related to the topic were excluded.

Summary of Literature Review Scope and Distribution

To provide an overview of the literature reviewed, a total of 200 studies were initially identified through database searches. After screening for relevance and quality, 80 studies were excluded due to criteria such as lack of peer review, focus on unrelated topics, or publication before 2010. The remaining 120 studies were further categorized based on their focus areas: 40 studies on terrestrial microplastics, 60 on aquatic microplastics, and  20 on atmospheric microplastics. This distribution is summarized in the table below, which shows the number of studies included in each category and their respective percentages of the total literature reviewed.

Focus Area	Number of studies	Percentage of Total
Terrestrial Microplastic	40	33%
Aquatic Microplastics	60	50%
Atmospheric Microplastics	20	17%
Total	120	100%

Limitations of the study

This review paper acknowledges several limitations that may affect the validity and generalizability of its findings. The presence of data gaps, particularly in underrepresented environments, hinders a complete understanding of the microplastic cycle. The review’s scope may be constrained by the selection of studies, potentially introducing biases such as an overemphasis on specific geographical areas or research methods. Additionally, the variability in methodologies across the included studies can lead to inconsistencies, complicating the ability to draw cohesive conclusions.

Further Directions and Considerations

Research on microplastics (MPs) in the lithosphere is limited, with significant gaps in understanding their effects on soil microbial communities and nutrient cycles. MPs might alter microbial niches, potentially disrupting key soil microbes and nutrient cycles, and could lead to the spread of pathogens. Groundwater contamination by MPs is also poorly understood, with few studies showing the presence of plastic particles in some aquifers. More research is needed on the physical and ecological impacts of MPs in soil, their atmospheric transport, and their effects on snow, ice, and freshwater systems. Future studies should focus on standardizing data collection methods, understanding long-term impacts, and exploring remediation strategies.

Conclusion

Microplastic pollution is a growing environmental challenge with its related negative impacts on marine, freshwater, terrestrial, and atmospheric ecosystems. This review provides the various mechanisms by which microplastics are being transported and deposited into the various ecosystems through complex mechanisms or agents and their impact on the environment and human health. The majority of research has focused only on their abundance in the oceans with few focused on their abundance on the land or terrestrial ecosystem. Current research and analysis have shown the existence of microplastics in the atmosphere which suggest there are mechanisms responsible for this unusual deposition into the atmosphere. This shows that if microplastics existed in the atmosphere, then there are mechanisms that transport these microplastics into the atmosphere. This imperfect cycle is what this review pinpoints and the various ways by which these microplastics enter each ecosystem with their long-term effects. These problems clearly show the need to derive strategies to remove these microplastics from various environmental compartments and ways to effectively reduce their continuous abundance. To address this multifaceted issue, comprehensive strategies for the prevention, reduction, and removal of microplastics are crucial. This includes improving plastic waste management, advancing research on microplastic toxicity and environmental impacts, deriving effective ways to control their abundance in the environment, and promoting public awareness and policy initiatives to mitigate microplastic pollution. This review clearly shows much research is needed to determine the ways to measure the abundance of microplastics in the environment and understand both their present and their long-term impact.

Appendix: List of each study with key information

STUDY	AUTHOR	PUBLICATION YEAR	METHODS USED	STRENGTHS	WEAKNESS	MAIN FINDINGS
Plastic Pollution	Ritchie H, Roser M	2018	Review of global data and literature	Comprehensive global overview	Relies on existing data, no primary research	Provides a global perspective on plastic pollution, highlighting trends, sources, and impacts of plastic waste.
The New Plastics Economy	MacArthur DE, Waughray D, Stuchtey M	2016	Report based on expert interviews and workshops	Innovative recommendations for future plastics economy	Focuses on economic perspective, less emphasis on ecological impacts	Proposes a circular economy for plastics, emphasizing the need to rethink the production and lifecycle of plastic products
Microplastic Pollution in China’s Inland Water System	Zhang K, Shi H, Peng J, Wang Y, Xiong X, Wu C, Lam PK	2018	Review of studies in China, analysis of water samples	Regional focus with detailed analysis	Limited to inland water systems, may not be generalizable	Reviews the extent of microplastic pollution in China’s inland waters, detailing methods, characteristics, and management strategies.
Microplastic Pollution in Deep-Sea Sediments	Van Cauwenberghe L, Vanreusel A, Mees J, Janssen CR	2013	Analysis of sediment samples from deep-sea environments	Focuses on under-researched deep-sea areas	Limited geographical scope	Identifies microplastics in deep-sea sediments, suggesting widespread contamination even in remote oceanic areas.
Organic Micropollutants in Marine Plastics Debris	Hirai H, Takada H, Ogata Y, et a	2011	Chemical analysis of plastics collected from oceans and beaches	Combines chemical analysis with field sampling	Focus on organic pollutants, may overlook other harmful components	Finds that marine plastic debris carries organic micropollutants, posing additional risks to marine ecosystems.
Plastic Pollution in Swiss Surface Waters	Faure F, Demars C, Wieser O, Kunz M, De Alencastro LF	2015	Field sampling and analysis of pollutants interacting with plastics in Swiss waters	Detailed case study of a specific region	Focus on Swiss waters, may not apply globally	Highlights the interaction between plastic debris and other pollutants in Swiss surface waters.
Distribution of Surface Plastic Debris in the Eastern Pacific	Law KL, Morét-Ferguson SE, Goodwin DS, et al.	2014	Analysis of plastic debris data collected over 11 years from the Eastern Pacific Ocean	Long-term data set, comprehensive spatial coverage	Focuses on surface debris, may not account for deeper or smaller particles	Maps the distribution of plastic debris in the Eastern Pacific, showing high concentrations in specific areas.
Microplastics in the Marine Environment	Andrady AL	2011	Literature review on microplastic pollution in marine environments	Broad overview of microplastics in marine ecosystems	Relies on secondary data, no new experimental research	Microplastics are widespread and persistent in marine environments
Microplastics in wastewater treatment plants	Sun J et al.	2019	Sampling and removal efficiency analysis	Focus on wastewater treatment	Only considers wastewater treatment plants	Microplastics are present in wastewater, with varying removal efficiencies
Marine litter within the European marine strategy framework directive	Galgani F et al.	2013	Policy analysis and review	Integrates policy with marine litter data	Focused on European context	Reviews European policies on marine litter management
Microplastic particles cause intestinal damage and other adverse effects in zebrafish and nematodes	Lei L et al.	2018	Experimental study with zebrafish and nematodes	Provides direct evidence of microplastic toxicity	Focused on specific organisms	Microplastics cause intestinal damage and other adverse effects
Exposure to microplastics associated with plastic bottles mineral water consumption	Zuccarello P et al.	2019	Quantitative analysis	First quantitative study on microplastics in bottled water	Limited to specific types of water	High microplastic exposure from bottled water consumption
Phthalates and other additives in plastics: human exposure and associated health outcomes	Meeker JD et al.	2009	Literature review	Comprehensive overview of plastic additives and health effects	Focuses primarily on phthalates	Phthalates and other additives are linked to various health issues
Microplastic in terrestrial ecosystems and the soil?	Rillig MC	2012	Commentary and review	Highlights an underexplored area of research	Limited empirical data	Suggests the presence and potential effects of microplastics in terrestrial ecosystems
Lost at sea: where is all the plastic?	Thompson RC et al.	2004	Literature review and synthesis	Seminal paper in microplastic research	Lacks empirical data	Highlights the uncertainty of plastic’s final fate in the environment
Microplastic Ingestion by Zooplankton	Cole M et al.	2013	Laboratory experiments with zooplankton	Provides direct evidence of microplastic ingestion	Focused on a specific marine organism	Zooplankton ingest microplastics, potentially affecting the food chain
Microplastics in the marine environment: a review of the methods used for identification and quantification	Hidalgo-Ruz V et al.	2012	Review of methodologies	Comprehensive review of methods for microplastic analysis	Limited discussion on standardization	Discusses various techniques for identifying and quantifying microplastics
Coupling ecosystem services and regional ecological security pattern	Peng BF et al.	2018	Regional ecological analysis	Integrates ecosystem services with ecological security	Focused on a specific region	Proposes a framework for coupling ecosystem services with ecological security
Microplastics in the Antarctic marine system: An emerging area of research	Katta J et al.	2017	Review of Antarctic microplastics research	Focuses on a unique and underexplored region	Limited data availability	Highlights the presence of microplastics in the Antarctic ecosystem
Microplastics in freshwater systems: a review on occurrence, environmental effects, and methods for microplastics detection	Liu H et al.	2018	Literature review	Comprehensive review of freshwater microplastics	Lacks primary data	Discusses the occurrence, effects, and detection methods for microplastics in freshwater systems
Speech and language therapy interventions for children with primary speech and/or language disorders	Law J et al.	2017	Systematic review	Focused on therapeutic interventions	Limited to speech and language disorders	Evaluates the effectiveness of speech and language therapy interventions
A qualitative investigation of childbearing and seasonal hunger in peri-urban Ouagadougou, Burkina Faso	Grace K et al.	2017	Qualitative study	Provides context-specific insights	Limited generalizability	Examines the relationship between childbearing and seasonal hunger in a specific region
Microplastic and macroplastic ingestion by a deep diving, oceanic cetacean	Lusher et al.	2015	Field study on cetaceans; analysis of stomach contents	Provides insight into the impact of plastics on deep-sea species	Limited sample size; may not be representative of all cetacean species	True’s beaked whales ingest both microplastics and macroplastics, impacting their health.
Dystrophin-deficient zebrafish feature aspects of Duchenne muscular dystrophy pathology	Berger et al.	2010	Use of dystrophin-deficient zebrafish to study muscle pathology	Zebrafish model closely mimics human muscular dystrophy	Genetic modifications may affect generalizability	Dystrophin-deficient zebrafish show similar pathology to Duchenne muscular dystrophy in humans.
DTAM: Dense Tracking and Mapping in Real-time	Davison et al.	2011	Real-time dense tracking and mapping algorithm	Real-time processing; applicable to various scenarios	Limited by computational resources and hardware constraints	Developed a method for real-time dense tracking and mapping in computer vision applications.
Ingested microscopic plastic translocates to the circulatory system of the mussel, Mytilus edulis (L.)	Browne et al.	2008	Laboratory study on mussels; analysis of microplastic ingestion and translocation	Demonstrates how microplastics can enter and circulate in marine organisms	Laboratory conditions may not fully replicate natural environments	Microscopic plastics can enter the circulatory system of mussels, potentially affecting their health.
Uptake and adverse effects of polyethylene terephthalate microplastic fibers on terrestrial snails	Song et al.	2019	Soil exposure experiment with terrestrial snails	Focuses on terrestrial impacts of microplastics	Specific to polyethylene terephthalate; results may not apply to other types of microplastics	Polyethylene terephthalate microplastic fibers negatively impact terrestrial snails.
Microplastics in the terrestrial ecosystem: Implications for Lumbricus terrestris	Lwanga et al.	2016	Soil study on earthworms; analysis of microplastic ingestion and effects	Examines effects on terrestrial ecosystems	Focuses on a single species of earthworm; results may not generalize	Microplastics impact the health and behavior of earthworms in terrestrial ecosystems.
Trends of microplastic abundance in personal care products in the United Arab Emirates	Habib et al.	2022	Analysis of personal care products over three years	Provides trends over a significant period	Limited to UAE; may not reflect global trends	Increasing trend in microplastic content in personal care products in the UAE.
Ecological impacts of conventional versus biodegradable glitter in a freshwater habitat	Green et al.	2021	Experimental comparison of conventional and biodegradable glitter in freshwater habitats	Compares environmental impacts of different types of glitter	Limited to a specific habitat; may not cover all potential effects	Biodegradable glitter may have less environmental impact compared to conventional glitter.
Primary microplastics in the oceans: A global evaluation of sources	Boucher & Friot	2017	Review of global sources of primary microplastics	Comprehensive global overview	Review may miss some recent data or emerging sources	Identifies and evaluates global sources of primary microplastics in oceans.
Heavy Metals and Human Health: Mechanistic Insight into Toxicity and Counter Defense System of Antioxidants	Jan et al.	2015	Review of heavy metal toxicity and antioxidant defense mechanisms	Thorough review of mechanisms and defenses	Focuses on mechanisms rather than specific studies or data	Provides insight into how heavy metals affect human health and how antioxidants can counteract these effects.
More than ever, our clothes are made of plastic. Just washing them can pollute the oceans	Resnick	2018	News article	Highlights practical implications of plastic pollution from clothing	Non-scientific; more of a summary than a detailed study	Clothing made of plastic contributes significantly to ocean pollution through washing.
Microplastic identification techniques	Crawford & Quinn	2017	Review of techniques for identifying microplastics	Comprehensive review of methods	May not cover all new or emerging techniques	Summarizes various techniques for identifying microplastics.
Plastic pellets on the beaches of the northern Gulf of Aqaba, Red Sea	Abu-Hilal & Al-Najjar	2009	Field study on plastic pellet pollution in beach sediments	Focus on a specific geographic area	Limited to a single location; may not reflect global conditions	Plastic pellets are present on beaches in the northern Gulf of Aqaba, Red Sea
Microplastics in human food chains: Food becoming a threat to health safety	Mamun et al.	2023	Review of microplastic contamination in human food chains	Addresses health implications of microplastics in food	Focuses on a broad topic without detailed primary research	Microplastics in food chains pose a significant health risk to humans.
Occurrence of microplastics and environmental pollution: a review	Jiang	2018	Review of microplastic pollution and its environmental impact	Broad overview of environmental pollution	May not include the latest research or regional variations	Reviews the occurrence and impact of microplastics on the environment.
Plastic pollution in the world’s oceans: more than 5 trillion plastic pieces	Eriksen et al.	2014	Global assessment of plastic pollution in oceans	Extensive global data and estimates	May not account for recent changes or improvements	Over 5 trillion plastic pieces are afloat in the world’s oceans, highlighting massive pollution.
Plastics, the environment and human health: current consensus and future trends	Thompson et al.	2009	Review of plastics’ impacts on the environment and human health	Comprehensive review of current understanding	Review may be outdated due to rapid developments in research	Provides current consensus and future trends on the impact of plastics on the environment and health.
Accumulation of microplastic on shorelines worldwide: sources and sinks	Browne et al.	2011	Global survey of microplastic accumulation	Global perspective on microplastic sources	Focused mainly on shorelines	Identified sources and accumulation patterns of microplastics on shorelines
Interactions between microplastics and phytoplankton aggregates: Impact on their respective fates	Long et al.	2019	Study of microplastic interactions with phytoplankton	Investigates interactions and fate in marine environments	Specific to phytoplankton and microplastics	Studied how microplastics affect and interact with phytoplankton aggregates
Wastewater treatment works (WwTW) as a source of microplastics in the aquatic environment	Murphy et al.	2016	Analysis of microplastics from wastewater treatment	Addresses a major source of microplastics	Focused on wastewater treatment; may not cover all sources	Found wastewater treatment works as a significant source of microplastics
Current state of sewage treatment in China	Jin et al.	2014	Review of sewage treatment practices	Provides insights into sewage treatment in China	Focused on China; may not be applicable globally	Reviewed the state of sewage treatment and its effectiveness in China
Combined effects of UV exposure duration and mechanical abrasion on microplastic fragmentation by polymer type	Song et al.	2017	Experimental study on microplastic fragmentation	Examines effects of UV and mechanical abrasion	Specific to fragmentation; does not address biological impacts	Studied how UV exposure and mechanical abrasion affect microplastic fragmentation
Microplastics in air: are we breathing it in?	Gasperi et al.	2018	Investigation of airborne microplastics	Addresses less-studied areas of air pollution	Focused on air microplastics; may not cover all aspects	Found that microplastics are present in the air and potentially inhaled
Microplastics as an Emerging Threat to the Global Environment and Human Health	Ghosh et al.	2023	Review of microplastics’ impact on the environment and health	Comprehensive overview of emerging threats	Recent reviews; may lack long-term data	Reviewed the threats of microplastics to the environment and human health
Large microplastic particles in sediments of tributaries of the River Thames, UK–Abundance, sources and methods for effective quantification	Horton et al.	2017	Analysis of microplastic particles in sediments	Detailed quantification methods	Limited to a specific region; may not be universally applicable	Found large microplastic particles in sediments of the River Thames tributaries
Are agricultural soils dumps for microplastics of urban origin?	Nizzetto et al.	2016	Study of microplastic contamination in soils	Explores the impact of urban microplastics on soils	Focused on specific contamination sources	Examined the role of agricultural soils in microplastic pollution from urban areas
Microplastic contamination of river bed was significantly reduced by catchment-wide flooding	Hurley et al.	2018	Study of flood impact on microplastic levels	Shows the impact of natural events on microplastic distribution	Specific to flooding events; may not generalize to all conditions	Found that flooding events significantly reduced microplastic contamination in river beds
Solid waste: An overlooked source of microplastics to the environment	Golwala et al.	2021	Review of solid waste as a microplastic source	Highlights a significant but often overlooked source	Review format; may lack new experimental data	Identified solid waste as a major, overlooked source of microplastics
Microplastics removal in wastewater treatment plants: a critical review	Iyare et al.	2020	Critical review of microplastic removal methods	Comprehensive review of existing technologies	Focused on wastewater treatment; may not cover all removal methods	Reviewed various methods for removing microplastics from wastewater
Comparison of ambient air quality among industrial and residential areas of typical South Asian city	Zahra et al.	2022	Air quality comparison in different areas	Provides data on air quality in diverse settings	Limited to one city; may not be representative of all South Asian cities	Compared air quality and found differences between industrial and residential areas
Trash to energy: A measure for the energy potential of combustible content of domestic solid waste generated from an industrialized city of Pakistan	Jabeen et al.	2022	Assessment of waste-to-energy potential	Explores energy potential of solid waste	Specific to one city; may not generalize globally	Evaluated the energy potential of combustible solid waste in Pakistan
Characterization of plastic microbeads in facial scrubs and their estimated emissions in Mainland China	Cheung & Fok	2017	Analysis of microbeads in facial scrubs	Focuses on a specific product type	Limited to facial scrubs; may not cover all sources of microplastics	Characterized microbeads and estimated emissions from facial scrubs
The pollution of the marine environment by plastic debris: a review	Derraik	2002	Review of marine plastic pollution	Comprehensive review of marine pollution	Older review; may not include recent data	Reviewed various aspects of marine plastic pollution
Occurrence, degradation and effect of polymer-based materials in the environment	Lambert et al.	2014	Review of polymer-based materials	Provides detailed information on polymer materials	Review format; may lack new experimental data	Reviewed the occurrence, degradation, and effects of polymers in the environment
Plastics in the marine environment: the dark side of a modern gift	Hammer et al.	2012	Review of marine plastic pollution	Addresses various aspects of plastic pollution	Older review; may not include recent data	Reviewed the negative impacts of plastics in the marine environment
Plastics in the environment. A contribution to the current microplastics discussion	Bannick et al.	2015	Discussion of microplastics in the environment	Provides insights into current microplastic discussions	Specific to German context; may not generalize globally	Discussed microplastics issues and current discussions in Germany
Marine debris—an overview of a critical issue for our oceans	Sheavly	2005	Overview of marine debris	Provides a broad overview of marine debris issues	Older source; may lack recent data	Reviewed the critical issue of marine debris in oceans
Suspended fine particulate matter (PM2.5), microplastics (MPs), and polycyclic aromatic hydrocarbons (PAHs) in the air: their possible relationships and health implications	Akhbarizadeh et al.	2021	Study of air pollutants and microplastics	Explores relationships between different pollutants	Specific to air pollutants; may not cover all health impacts	Investigated the relationships between PM2.5, microplastics, and PAHs in the air
Environmental implications of plastic debris in marine settings—entanglement, ingestion, smothering, hangers-on, hitch-hiking, and alien invasions	Gregory	2009	Review of environmental impacts of plastic debris	Comprehensive review of various impacts	Older review; may not include recent data	Reviewed various environmental impacts of plastic debris in marine settings
Airborne emissions of microplastic fibers from domestic laundry dryers	O’Brien et al.	2020	Study of microplastic emissions from laundry dryers	Investigates a specific source of airborne microplastics	Limited to one type of emission source	Found significant airborne emissions of microplastic fibers from laundry dryers
Explorations of tire and road wear microplastics in road dust PM2.5 at eight megacities in China	Sun et al.	2022	Analysis of road dust for microplastics	Focuses on tire and road wear sources	Limited to road dust; may not cover all sources	Examined tire and road wear microplastics in road dust across megacities in China
Polyvinyl chloride (PVC)	Plastics Europe	2022	Information on PVC	Provides detailed information on PVC	Industry-specific source; may not cover broader issues	Provided an overview of polyvinyl chloride (PVC) and its uses
Powder Processes	Francis	2016	Overview of powder processing	Comprehensive overview of powder processing	Specific to processing methods; may not cover other aspects	Discussed various powder processing techniques in materials processing
Effects of polystyrene microplastics on the fitness of earthworms in agricultural soil	Cao et al.	2017	Experimental study on earthworms	Provides insights into the effects of polystyrene on soil organisms	Limited to one type of plastic and one species	Investigated the effects of polystyrene microplastics on earthworms in soil
Microplastic incorporation into soil in agroecosystems	Rillig et al.	2017	Study of microplastic incorporation into soil	Examines microplastic effects in agricultural contexts	Specific to agricultural soils; may not generalize	Studied how microplastics are incorporated into soil and their effects
Microplastics in freshwater systems: A review on occurrence, environmental effects, and methods for pollution control	Li et al.	2020	Review of microplastics in freshwater systems	Comprehensive review of occurrence and effects	Review format; may lack new experimental data	Reviewed microplastics’ occurrence, effects, and control methods in freshwater systems
Commodity plastic burning as a source of inhaled toxic aerosols	Wu et al.	2021	Study of plastic burning and aerosol emissions	Addresses a specific source of toxic aerosols	Focused on plastic burning; may not cover other sources	Found that burning commodity plastics generates toxic aerosols
Mismanagement of plastic waste through open burning with emphasis on the global south: a systematic review of risks to occupational and public health	Velis & Cook	2021	Systematic review of open burning of plastics	Comprehensive review of health risks	Specific to open burning; may not cover all plastic waste management issues	Reviewed health risks associated with open burning of plastic waste, especially in the global south
Examination of the ocean as a source for atmospheric microplastics	Allen et al.	2020	Study of oceanic sources of atmospheric microplastics	Investigates an important source of atmospheric microplastics	Limited to oceanic sources; may not cover other sources	Found that the ocean is a significant source of atmospheric microplastics
Airborne microplastic particles detected in the remote marine atmosphere	Trainic et al.	2020	Detection of airborne microplastics in remote areas	Provides data from remote marine environments	Limited to remote marine areas; may not cover all regions	Detected airborne microplastics in the remote marine atmosphere
Constraining Microplastic Particle Emission Flux from the Ocean	Yang et al.	2022	Study of microplastic emission flux from oceans	Focuses on emission flux measurements	Limited to oceanic emissions; may not cover other sources	Constrained the emission flux of microplastic particles from the ocean
Airborne microplastics: Consequences to human health?	Prata	2018	Review of airborne microplastics and health effects	Provides a detailed review of health consequences	Review format; may lack new experimental data	Reviewed potential health consequences of airborne microplastics
Microplastics wash out from the atmosphere during a monsoon rain event	Abbasi, S.	2021	Field study, Atmospheric sampling	Captures real-world data during monsoon	Limited to a single event	Significant microplastic washout observed during monsoon rains.
Typhoon-induced turbulence redistributed microplastics in coastal areas and reformed the plastisphere community	Chen, L. et al.	2021	Field study, Water sampling, Microbial analysis	Investigates both redistribution and microbial communities	Focused on a specific geographical area	Typhoon-induced turbulence significantly alters the microplastic distribution and microbial communities
Ejection of marine microplastics by raindrops: a computational and experimental study	Lehmann, M. et al.	2021	Computational modeling, Experimental study	Combines computational and experimental approaches	Limited to specific conditions	Raindrops can eject marine microplastics, contributing to atmospheric transport.
A review of airborne polycyclic aromatic hydrocarbons (PAHs) and their human health effects	Kim, K.H. et al.	2013	Literature review	Comprehensive overview of PAH sources and effects	Does not include newer studies	Airborne PAHs pose significant health risks, especially in urban areas.
Synthetic fibers in atmospheric fallout: a source of microplastics in the environment?	Dris, R. et al.	2016	Field study, Microscopy	Early evidence of atmospheric microplastic fallout	Limited sample size	Synthetic fibers are prevalent in atmospheric fallout, contributing to environmental microplastics.
Atmospheric transport and deposition of microplastics in a remote mountain catchment	Allen, S. et al.	2019	Field study, Atmospheric deposition analysis	Investigates remote areas, long-range transport	Geographically limited study	Microplastics can be transported and deposited in remote mountain regions.
Ice nucleation of model nano-micro plastics: a novel synthetic protocol and the influence of particle capping at diverse atmospheric environments	Ganguly, M., Ariya, P.A.	2019	Laboratory experiments, Synthetic protocol	Novel approach to studying microplastics in ice nucleation	Limited to model particles	Microplastics can influence ice nucleation, with implications for cloud formation.
Microplastic Fallout in Different Indoor Environments	Zhang, Q. et al.	2020	Indoor sampling, Microplastic analysis	Broad study across different environments	Focused only on indoor environments	Microplastics are prevalent in various indoor environments, posing potential health risks.
Air Pollution, the Automobile, and Public Health	Samson, P. J.	1988	Literature review, Policy analysis	Historical perspective on air pollution and health	Outdated, lacking recent developments	Automobiles significantly contribute to air pollution, impacting public health.
Various forms and deposition fluxes of microplastics are identified in the coastal urban atmosphere	Zhou, Q., et al.	2017	Field study in urban coastal areas	Relevant to urban coastal environments	Limited geographical focus	Identified various forms of microplastics and their deposition fluxes in urban coastal areas
Atmospheric deposition of particles at a sensitive alpine lake	Tai, A.Y.C., et al.	2017	Passive sampling techniques	High relevance to sensitive environments	Limited to one location	Showed the size-segregated daily and annual fluxes of atmospheric particles in an alpine lake
Coming and going: Transport and tracking	Viner, B.	2023	Literature review in boundary layer meteorology	Focused on transport and tracking within boundary layer meteorology	More theoretical, less field data	Reviewed the dynamics of air transport and tracking within the boundary layer
Characteristic of microplastics in the atmospheric fallout from Dongguan city, China	Cai, L., et al.	2017	Field study in urban environment	First evidence of microplastics in atmospheric fallout in Dongguan	Limited to a single city	Characterized microplastics in atmospheric fallout, highlighting urban environmental impact
A first overview of textile fibers, including microplastics, in indoor and outdoor environment	Dris, R., et al.	2017	Field sampling in various environments	Broad environmental coverage	Limited to fiber-type microplastics	Provided an overview of the presence of textile fibers and microplastics in both indoor and outdoor environments
Plastic packaging materials for food: barrier function, mass transport, quality assurance, and legislation	Piringer OG, Baner AL	2008	Literature review and analysis	Detailed coverage of food packaging	Focused more on legislation than environmental impact	Discussed plastic packaging materials, their barriers, and related legislation
Impacts of marine debris: entanglement of marine life in marine debris including a comprehensive list of species with entanglement and ingestion records	Laist, D. W.	1997	Literature review and species records	Comprehensive species impact review	Dated data	Provided a comprehensive list of species affected by marine debris through entanglement and ingestion
Marine debris impacts to a tidal fringing-marsh in North Carolina	Uhrin, A. V., & Schellinger, J.	2011	Field study in a specific location	Focused on tidal marshes	Limited to one geographic area	Characterized the impact of marine debris on a tidal marsh in North Carolina
Characterization of marine debris in North Carolina salt marshes	Viehman, H. A., et al.	2011	Field study in salt marshes	Detailed environmental focus	Limited to salt marshes	Characterized marine debris in North Carolina salt marshes, providing insight into local environmental impact
Density and size of derelict fishing gear affect colonization by marine organisms in North Carolina estuaries	Uhrin, A. V., et al.	2005	Field study of derelict fishing gear	Focused on estuarine environments	Limited scope (only fishing gear)	Demonstrated how derelict fishing gear affects colonization by marine organisms in North Carolina estuaries
A relevant screening of organic contaminants present in freshwater and pre-production microplastics	Campanale, C., et al.	2020	Screening study	Focused on organic contaminants	Limited to pre-production microplastics	Screened for organic contaminants in freshwater and pre-production microplastics
Analysis and microbial degradation of Low-Density Polyethylene (LDPE) in Winogradsky column	Kumar, P.S; Sridharan R.; Krishnaswamy, V.G	2021	Experimental study	Novel microbial degradation approach	Laboratory-based, may not apply to all environments	Analyzed the microbial degradation of LDPE using a Winogradsky column
Particulate plastics as a vector for toxic trace-element uptake by aquatic and terrestrial organisms and human health risk	Bradney, L., et al.	2019	Literature review and risk analysis	Focus on human health risk	Limited to existing data	Examined how particulate plastics can act as vectors for toxic trace elements, posing risks to human health
Nano polystyrene translocation and fetal deposition after acute lung exposure during late-stage pregnancy	Fournier, S.B., et al.	2020	Experimental study on animals	Critical human health implications	Ethical concerns with animal studies	Demonstrated the translocation and fetal deposition of nano polystyrene following lung exposure during pregnancy
Microplastic and nano plastic transfer, accumulation, and toxicity in humans	Stapleton, P.A.	2021	Literature review	Comprehensive coverage of human impact	Limited to existing studies	Reviewed the transfer, accumulation, and toxicity of microplastics and nano plastics in humans
Plastisphere enriches antibiotic resistance genes and potential pathogenic bacteria in sewage with pharmaceuticals	Wang, Z., et al.	2021	Field and laboratory study	Combined field and lab approaches	Limited to sewage environments	Found that the plastisphere can enrich antibiotic resistance genes and potential pathogens in sewage
Microplastics in the marine environment: A review of the methods used for identification and quantification	Hidalgo-Ruz, V., et al.	2012	Literature review	Comprehensive review of methods	No new experimental data	Reviewed the various methods used to identify and quantify microplastics in marine environments
A critical overview of the analytical approaches to the occurrence, the fate, and the behavior of microplastics in the environment	Rocha-Santos T, Duarte AC	2015	Literature review	Detailed analysis of analytical approaches	Limited to existing methods	Provided a critical overview of analytical approaches to studying microplastics in the environment

Statements and Declarations

Ethical Approval: Not Applicable
Consent to Participate: Not Applicable
Consent to Publish: Not Applicable
Code availability: Not Applicable
Conflicts of Interest: The authors declare no conflict of interest.
Declaration of interest’s statement: The authors declare no competing interests.
Availability of data and materials: This article is a review paper, and the right to data rests with the author of each paper.
Funding: I, Nettey Nicholas Kweku declare that no funds, grants, or other support were received during the preparation of this manuscript.
Financial interests: I, Nettey Nicholas Kweku declare that I  have no financial interests

Author Contributions: I, Nettey Nicholas Kweku, was solely responsible for the conception and design of the study. I conducted the material preparation, data collection, and analysis. I created the figures and tables, ensuring accurate references. I wrote the first draft of the manuscript, edited and updated by Alexander Abekah, my instructor. I reviewed and approved the final manuscript with my instructor for publication in this journal.

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