Microplastic Pollution: An In-depth Review of its Sources, Formation Mechanisms, Quantification Techniques, Environmental Impacts, Toxicological Effects and Remediation Strategies

Corresponding author: Nkin Gift Kiisi Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Microplastic Pollution: An In-depth Review of its Sources, Formation Mechanisms, Quantification Techniques, Environmental Impacts, Toxicological Effects and Remediation Strategies Gift Kiisi Nkin * Department of Chemistry, Faculty of Science, Rivers State University, P.M.B 5080 Nkpolu-Oroworukwo, Port Harcourt, Rivers State, Nigeria. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 Publication history: Received on 18 May 2025; revised on 22 June 2025; accepted on 28 June 2025 Article DOI: https://doi.org/10.30574/wjarr.2025.27.1.2483 Abstract Microplastic pollution has become a prevalent environmental issue, with particles smaller than 5 millimeters infiltrating virtually every ecosystem. This review provides a comprehensive analysis of microplastic sources, formation mechanisms, quantification techniques, environmental impacts, toxicological effects, and remediation strategies. Microplastics originate from both primary and secondary sources. Primary microplastics include deliberately manufactured particles such as microbeads and synthetic fibers from textiles. Secondary microplastics result from the degradation of larger plastic debris due to environmental factors such as UV radiation, mechanical abrasion, and chemical weathering. Land-based activities, including industrial processes, agriculture, and improper waste disposal, contribute tremendously to microplastic pollution, with land-based sources responsible for 80–90% of marine microplastic contamination. Accurate quantification of microplastics is imperative for assessing pollution levels and informing reduction strategies. Techniques such as Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM) are commonly used to identify and characterize microplastic particles. Microplastics cause remarkable threats to aquatic ecosystems. They can physically damage organisms through ingestion, resulting in blockages, malnutrition, and death. Moreover, microplastics serve as vectors for injurious chemicals, including persistent organic pollutants (POPs), which can leach into the environment and accumulate in the food chain. The presence of microplastics in marine environments disrupts habitats and affects biodiversity, with potential long-term consequences for ecosystem stability. The ingestion of microplastics has been linked to different adverse health effects in humans and wildlife. In humans, microplastics have been detected in biological samples like feces, saliva, blood, and placenta, raising concerns about potential health risks. Animal studies show that microplastics can cause oxidative stress, inflammation, and genotoxicity, even at low concentrations. Tackling microplastic pollution requires a multifaceted approach circumscribing prevention, removal, and mitigation. Microplastic pollution is a complex and escalating issue that necessitates concerted global efforts. Effectual management requires a combination of reducing plastic generation, improving waste management, advancing remediation technologies, and conducting further research to comprehend the full extent of microplastic impacts on health and ecosystems. Synergetic actions at the international, national, and local levels are crucial to mitigate the prevalent threat caused by microplastics and protect environmental and public health. Keywords: Microplastic Pollution; Sources; Formation Mechanism; Microplastic Detection; Environmental and Health Impacts; Microplastic Toxicity; Microplastic Mitigation World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 229 Graphical abstract 1. Introduction Microplastics, defined as plastic particles less than 5 millimeters in size, have appeared as a widespread environmental pollutant. Their ubiquity spans oceans, freshwater bodies, soils, air, and even remote regions like the Arctic and Mount Everest [1, 18, 17]. These particles start from both primary sources, such as microbeads in personal care products, and secondary sources, resulting from the degradation of larger plastic items under environmental stressors [17, 18]. Microplastics are categorized into primary and secondary types. Primary microplastics are intentionally manufactured tiny plastic particles, including microbeads used in cosmetics and personal care products, and plastic pellets (nurdles) used in industrial manufacturing. Secondary microplastics result from the degradation of larger plastic items like bottles, bags, and synthetic clothing fibers due to environmental factors such as sunlight, heat, and mechanical wear [2, 18, 42]. The degradation of plastics into microplastics is influenced by various environmental factors. Ultraviolet (UV) radiation from sunlight, thermal degradation, oxidation, and mechanical abrasion give rise to the fragmentation of larger plastic debris into smaller particles [3]. These microplastics are then transported via various pathways, including wastewater runoff, entering freshwater and marine systems, and posing tremendous environmental threats. Microplastics have been detected in various biological samples, including feces, sputum, saliva, blood, and placenta, showing widespread human exposure. Their small size allows them to penetrate biological barriers, leading to potential health risks. Studies have linked microplastic exposure to various health issues, such as cancer, intestinal, pulmonary, cardiovascular, infectious, and inflammatory diseases [100]. In aquatic ecosystems, microplastics pose significant threats to marine life. Organisms ingest microplastics, leading to alterations in gastrointestinal tract physiology, immune system depression, oxidative stress, cytotoxicity, differential gene expression, and growth inhibition [4, 100, 105, 107]. The bioaccumulation of microplastics in aquatic organisms can have adverse effects on the aquatic ecosystem, with potential transmission of microplastics to humans and birds. Precise quantification of microplastics is challenging due to their small size and diverse forms. Traditional methods include visual identification under microscopes, but these can be time-consuming and may not detect all types of microplastics. Advanced techniques such as Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy offer more precise identification and quantification by analyzing the chemical composition of the particles [5, 88, 89, 93, 94]. Efforts to mitigate microplastic pollution involve various remediation strategies. These include coagulation, membrane bioreactors, sand filtration, adsorption, photocatalytic degradation, electrocoagulation, and magnetic separation. Each method has its advantages and limitations, and often, a combination of these approaches is employed to enhance efficiency. A promising development in microplastic removal is the use of bio-inspired materials. Researchers at the University of Wuhan have developed a sponge made from cotton and squid bone that can absorb 99.9% of microplastics in water [6]. This sponge has shown remarkable reusability and scalability, offering a potential solution to the growing problem of microplastic pollution [6]. Microplastics represent a significant environmental and public health challenge. Their widespread presence in various ecosystems and potential health impacts necessitate urgent action. Implementing effective remediation strategies, reducing plastic usage, and promoting behavioral changes are essential steps toward mitigating microplastic pollution. Continued research and innovation are crucial in developing sustainable solutions to address this pervasive issue [6,5,2,4]. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 230 2. Sources of Microplastics Microplastics are prevelent environmental pollutants resulting from both primary and secondary sources. Understanding these sources is important for developing strategies to mitigate their impact. Figure 1 Sources of Microplastics(17 Modified) 2.1. Primary Sources of Microplastics Primary microplastics are purposely manufactured plastic particles designed to be small, typically less than 5 millimeters in size, from the outset. Unlike secondary microplastics, which form when larger plastic items degrade over time due to environmental factors. Primary microplastics are directly introduced into the environment through various human activities [7]. Their extensive presence in ecosystems and potential health implications underscore the importance of understanding their origins and the reasons for their production. Below are some examples of primary microplastics sources [8]. 2.2. Personal Care and Cleaning Products Microbeads are tiny plastic particles, typically less than 1 millimeter in diameter. Microbeads, small plastic particles used in exfoliating products like facial scrubs and toothpaste, are major contributors to primary microplastics. These microbeads are often made from polyethylene and are not biodegradable. Studies have found that products such as facial scrubs can contain up to 350,000 microbeads per tube, and toothpaste can have between 1,700 to 6,400 microbeads per gram. These particles are washed down drains and are not completely removed by wastewater treatment plants, leading to their release into aquatic environments [9, 7, 8]. 2.2.1. Prevalence and Composition of Microbeads Microbeads are purposely incorporated into personal care and cleaning products for their exfoliating and abrasive properties. They are typically made up of synthetic polymers like polyethylene, polypropylene, or polystyrene. These materials are chosen for their durability and effectiveness in cleansing. In facial scrubs, for instance, a single tube can contain up to 350,000 microbeads. Toothpaste products may contain between 1,700 to 6,400 microbeads per gram. These figures highlight the significant quantities of microbeads present in everyday personal care items [10]. 2.2.2. Environmental Impact of Microbeads After use, microbeads are washed down the drain and enter wastewater systems. Due to their small size and buoyancy, they always pass through wastewater treatment plants without being filtered out. This inefficiency leads to the release of microbeads into rivers, lakes, and oceans. Once in aquatic environments, microbeads can be ingested by marine organisms, leading to potential physical harm and the accumulation of toxic substances. These particles can absorb and concentrate pollutants like pesticides and polycyclic hydrocarbons, which may then enter the food chain [11]. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 231 2.2.3. Global Response and Legislation on Microbeads Recognizing the environmental threat constituted by microbeads, several countries have enacted legislation to prohibit their use in personal care and cleaning products. For example, the United States passed the Microbead-Free Waters Act in 2015, mandating the phase-out of microbeads in rinse-off cosmetics by July 2017. Similarly, the European Union and other nations have implemented related bans. These legislative actions have prompted manufacturers to seek alternative exfoliating agents, such as natural materials like jojoba beads, ground walnut shells, and sugar crystals, which are biodegradable and less harmful to the environment [12]. 2.2.4. Consumer Awareness and Alternatives of Microbeads Consumer awareness plays an important role in mitigating the impact of microbeads. By choosing products labeled as "microbead-free" or "biodegradable," consumers can reduce their contribution to microplastic pollution. Additionally, opting for natural exfoliating products and supporting brands that prioritize environmental sustainability can drive industry-wide change. Educational campaigns and clear product labeling are vital in empowering consumers to make informed choices and encourage the adoption of environmentally friendly alternatives [13]. 2.3. Synthetic Textiles Synthetic fibers from clothing, such as polyester, nylon, and acrylic, shed microplastics during washing. Each wash can release hundreds of thousands of fibers, which pass through wastewater treatment plants and enter water bodies. These fibers are also found in biosolids applied to soil, contributing to terrestrial microplastic pollution [14, 15]. 2.3.1. Microplastics from Synthetic Fibers in Clothing: Environmental Pathways and Impacts Synthetic fibers, such as polyester, nylon, and acrylic, have become ubiquitous in modern textiles due to their durability, affordability, and versatility. However, these materials are notably contributors to microplastic pollution, particularly through the shedding of microfibers during washing processes. Each laundry cycle can release a substantial number of microfibers into the environment, leading to widespread contamination of aquatic and terrestrial ecosystems [15, 14]. 2.3.2. Shedding of Microfibers During Washing The primary mechanism by which synthetic textiles release microplastics is through mechanical abrasion during washing. As garments made from polyester, nylon, and acrylic fibers are agitated in washing machines, small fibers detach from the fabric. These microfibers are typically less than 5 millimeters in length and are small enough to pass through standard wastewater treatment plant filters. For instance, a single fleece jacket can release up to 250,000 microfibers per wash cycle [16, 18]. 2.3.3. Transport and fate of microfibers in Wastewater Systems Once released, these microfibers enter the wastewater system, where they often evade filtration due to their minute size. While some microfibers are captured by advanced treatment processes, a significant portion remains in the effluent and is discharged into rivers, lakes, and oceans. Studies have shown that up to 35% of microplastics in the ocean originate from synthetic textile fibers released during washing [17] . Furthermore, microfibers can be retained in the sludge produced by wastewater treatment plants. This biosolid is often used as fertilizer in agriculture, leading to the introduction of microplastics into soil ecosystems. Research shows that biosolids can contain hundreds of microplastic particles per gram, with microfibers being the most prevalent type [18]. 2.3.4. Environmental and Ecological Impacts of microfibers The pervasive existence of microfibers in aquatic environments contributes several ecological risks. Marine organisms, ranging from zooplankton to large fish, can ingest these particles, mistaking them for food. This ingestion can lead to physical harm, such as blockages or internal injuries, and may also result in the accumulation of toxic substances adsorbed onto the microfibers. Consequently, microfibers can enter the food chain, potentially affecting human health through seafood consumption [19]. In terrestrial ecosystems, the application of biosolids containing microfibers to agricultural land introduces these pollutants into the soil. Microfibers can affect soil structure and function, potentially impacting plant growth and soil organism health. Additionally, the persistence of microfibers in soil raises concerns about their long-term environmental impact [20]. 2.4. Tire Wear As vehicles operate, tire abrasion releases microplastics into the environment. These particles are transported through different pathways into rivers, lakes, and oceans. Tire wear is considered a tremedous source of microplastics, World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 232 particularly in urban areas [21]. It is a significant yet often overlooked contributor to microplastic pollution, especially in urban environments. As vehicles operate, the friction between tires and road surfaces causes the release of tiny particles known as tire wear particles (TWPs) [21, 22]. These particles, which are typically smaller than 5 millimeters, consist of a mixture of rubber, asphalt, and other materials. Once released, they enter the environment via various pathways, including stormwater runoff, atmospheric deposition, and direct deposition on road surfaces [21]. 2.4.1. Pathways of Tire Wear Particles into the Environment Tire wear particles (TWPs) are a significant and often overlooked source of microplastic pollution, entering the environment through various pathways. These particles, resulting from the abrasion of tires on road surfaces, contribute to environmental degradation in multiple ways. One of the common pathways for TWP pollution is stormwater runoff. During rainfall, tire wear particles are washed off road surfaces into storm drains, which eventually discharge into rivers, lakes, and oceans. A study conducted in Queensland, Australia, found that during rain events, approximately 95% of microplastics in stormwater were tire wear particles. This highlights the significant role of TWPs in contributing to aquatic microplastic pollution. The presence of synthetic rubber in tires, which contains up to 2,500 chemicals, exacerbates the issue, as these substances can leach into water bodies, posing risks to aquatic life and ecosystems [22, 21]. Another concerning pathway is atmospheric deposition. Some tire wear particles are light enough to become airborne. These particles can travel long distances, even reaching remote areas like the Arctic. Research indicates that the smallest tire wear particles can remain suspended in the atmosphere for nearly a month, allowing them to disperse globally. This extensive distribution raises concerns about the impact of TWPs on ecosystems far from their source, including potential effects on the Arctic's albedo, which could accelerate ice melting and global warming. Direct deposition is another significant pathway, especially in areas with high traffic density. In such regions, tire wear particles can accumulate directly on road surfaces and adjacent environments. Over time, these particles can degrade, contributing to soil and water pollution. The accumulation of TWPs in urban areas accentuates the need for effective management strategies to mitigate their environmental impact. Addressing the issue of tire wear particle pollution requires a multifaceted approach, including improving stormwater management systems, developing tire materials that shed fewer particles, and increasing public awareness about the environmental impact of tire wear. By understanding and mitigating the pathways through which TWPs enter the environment, we can take steps toward reducing their harmful effects on ecosystems and human health [22]. 2.4.2. Environmental Impact of Tire Wear The accumulation of tire wear particles (TWPs) in aquatic environments poses significant environmental risks, impacting both aquatic life and human health. These particles, primarily composed of synthetic rubbers, fillers, and additives, are released into the environment through vehicle tire wear. Once in aquatic systems, TWPs can have harmful effects on different aspects of the ecosystem. One of the primary concerns is the toxicity of TWPs to aquatic organisms. Studies have shown that leachates from TWPs can induce oxidative stress, inflammation, and histopathological changes in aquatic species [23]. For instance, research on black-spotted frogs revealed that exposure to TWP leachates led to increased levels of reactive oxygen species and activation of immune-related signaling pathways, indicating significant health impacts on these organisms [23, 24, 26]. Additionally, exposure to TWP leachates has been linked to acute mortality in coho salmon, with concentrations as low as 0.095 µg/L causing lethal effects [24]. Beyond direct toxicity, TWPs contribute to bioaccumulation in the food chain. Microplastics, including those from tire wear, can be ingested by marine organisms ranging from plankton to larger fish and mammals. This ingestion can lead to the accumulation of toxic substances within the organisms, which may then be transferred up the food chain, potentially affecting human health through seafood consumption. Furthermore, the physical presence of TWPs in aquatic environments can cause harm to marine life. Ingested microplastics can lead to physical injury, blockages in digestive systems, and malnutrition. For example, studies have observed that ingestion of microplastics can cause physical harm to marine animals, leading to injury or death [25, 26]. Additionally, these particles can block digestive systems, leading to malnutrition or starvation. The environmental impact of tire wear particles is multifaceted, encompassing toxicity, bioaccumulation, and physical harm to aquatic life [24, 26]. Addressing this issue requires comprehensive strategies, including reducing tire wear, improving road runoff management, and conducting further research to fully understand the extent of the problem and develop effective solutions. 2.4.3. Tire Wear Urban Challenges and Solutions Urban environments, notably those with high vehicle density and extensive impervious surfaces, are particularly vulnerable to microplastic pollution originating from tire wear. The friction between tires and road surfaces generates tiny particles, known as tire wear particles (TWPs), which are a significant source of microplastics in urban areas. These particles are often washed into stormwater systems during rainfall, leading to their accumulation in water bodies and posing threats to aquatic ecosystems. The combination of heavy traffic and limited natural filtration systems World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 233 exacerbates the issue, making it crucial to implement effective mitigation strategies. One of the primary approaches to addressing this issue is enhanced road cleaning. Regular street sweeping, especially before anticipated rainfall, can effectively remove accumulated TWPs from road surfaces. For instance, in the United Kingdom, authorities have utilized detailed traffic data to target the busiest roads for cleaning, ensuring that areas with the highest potential for pollution are addressed punctually [27]. Additionally, employing advanced cleaning technologies, such as truck-mounted sweepers equipped with high-efficiency filters, can capture finer particles, preventing them from entering stormwater systems. Improved stormwater management is another crucial strategy. Upgrading stormwater infrastructure to include filtration systems can greatly reduce the amount of TWPs entering water bodies. For example, in Australia, researchers have assessed the effectiveness of stormwater treatment devices like mesh bags retrofitted to drains, which have shown up to an 88% reduction in microplastics in treated water [28]. Moreover, constructing stormwater wetlands has proven effective in capturing and removing microplastics from runoff, with studies indicating a significant decrease in particle concentration after passing through these systems. Incorporating such infrastructures can improve the resilience of urban areas against microplastic pollution. Public awareness campaigns play a pivotal role in mitigating microplastic pollution from tire wear. Educating the public on the environmental impact of TWPs can encourage responsible driving habits and support for policies aimed at reducing microplastic pollution. Campaigns can focus on promoting practices such as maintaining proper tire pressure, avoiding sudden accelerations and braking, and reducing vehicle weight, all of which can decrease tire wear. Additionally, raising awareness about the importance of using public transportation, cycling, and walking can contribute to reducing the overall number of vehicles on the road, thereby lessening the generation of TWPS. Incorporating these strategies into urban planning and policy-making can significantly mitigate the impact of tire wear on microplastic pollution. By enhancing road cleaning, improving stormwater management, and fostering public awareness, cities can move towards a more sustainable and environmentally friendly future. Collaborative efforts between governments, communities, and industries are crucial to address this pressing environmental challenge effectively [27, 28]. 2.4.4. Global Perspective of Tire Wear Tire wear is a global issue, with studies indicating that it is one of the largest sources of microplastics in the environment. For example, a study published in Nature Communications estimated that 52,000 tons of the smallest tire wear particles end up in the sea each year, while 20,000 tons are deposited in remote regions like the Arctic [29]. 2.4.5. Research and Future Directions of Tire Wear Tire wear particles (TWPs) have emerged as a significant yet often overlooked source of microplastic pollution, especially in urban environments. These particles are generated through the abrasion of tires on road surfaces, releasing a complex mixture of synthetic rubbers, carbon black, oils, and chemical additives. Due to their small size and lightweight nature, TWPs can be transported over long distances by wind and water, leading to extensive environmental contamination. The accumulation of these particles in various ecosystems raises concerns about their potential impacts on both the environment and human health. Quantifying the emissions of TWPs is a critical step in understanding their environmental impact. Recent studies have provided estimates of TWP emissions, with per capita emissions ranging from 0.23 to 4.7 kg per year, averaging around 0.81 kg per year globally. In urban areas, where vehicle density is high, these emissions can be significantly higher. For instance, in the San Francisco Bay area, it was estimated that approximately 15 to 19 million kilograms of TWP are emitted annually, with a substantial portion entering the bay through stormwater runoff [30]. These figures underscore the need for accurate measurement techniques to assess the scale of TWP pollution and to inform mitigation strategies. Assessing the environmental impact of TWPs involves examining their effects on various ecosystems. Studies have shown that TWPs can be ingested by aquatic organisms, leading to adverse effects on feeding, growth, and behavior. For example, exposure to TWPs has been found to affect the growth and swimming behavior of marine species such as the silverside Menidiaberyllina and the mysid shrimp Americamysisbahia [30]. Additionally, the leaching of toxic chemicals from TWPs, such as the preservative 6PPD-quinone, has been linked to the mortality of coho salmon in freshwater systems. These findings highlight the potential for TWPs to disrupt aquatic ecosystems and the need for further research to fully understand their ecological risks. In response to the growing concern over TWP pollution, there is a concerted effort to develop sustainable alternatives to traditional tire materials. Research is underway to create tires using biobased materials, such as guayule and dandelion rubber, which may reduce the release of harmful particles upon wear. Moreover, innovations in tire design aim to enhance durability and reduce wear, thereby decreasing the overall generation of TWPs. For instance, the development of tires with optimized tread patterns and compounds can minimize abrasion and extend tire life. These advancements not only promise to mitigate environmental pollution but also contribute to the sustainability of the automotive industry [30]. The issue of TWP pollution necessitates a multifaceted approach, combining rigorous research, technological innovation, and public awareness. By quantifying TWP emissions, assessing their environmental impact, and developing sustainable alternatives, it is possible to reduce the ecological World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 234 footprint of tire wear and move towards a more sustainable future. Continued collaboration among researchers, industry stakeholders, and policymakers is essential to address this pressing environmental challenge effectively [30]. 2.5. Paints and Coatings Paints, varnishes, and coatings always contain microplastics to enhance durability and finish. These microplastics are released during application, wear, and removal processes. For example, marine coatings can release microplastics into the ocean, contributing to marine pollution [31]. while paints, varnishes, and coatings serve essential functions in enhancing the durability and appearance of surfaces, their contribution to microplastic pollution cannot be overlooked. By adopting sustainable practices and materials, it is possible to mitigate the environmental impact of these products and protect our ecosystems [31]. 2.5.1. Composition and Function of Microplastics in Coatings Microplastics are added to coatings to enhance attributes such as opacity, scratch resistance, and durability. Common polymers used include polyurethanes, polyesters, polyacrylates, polystyrenes, alkyls, and epoxies. These additives contribute to the longevity and resilience of the coatings, making them suitable for various applications, including marine environments, road markings, and building exteriors. However, the very properties that make these coatings effective also facilitate the release of microplastics into the environment [32]. 2.5.2. Release Mechanisms of Microplastics from Coatings Microplastics enter the environment through several pathways, particularly from the degradation and handling of coatings. These pathways include the application process, wear and tear, maintenance activities, and the removal of coatings. During the application of paints and coatings, especially in industrial settings, overspray and spillage can result in microplastic particles being released into the air and subsequently settling into water bodies. For example, when ships are painted, the excess paint that drifts away can contain microplastics, which in time find their way into the ocean. This not only contributes to marine pollution but also poses risks to aquatic life as these microplastics can be ingested by marine organisms, leading to potential health hazards [33]. Over time, the continuous exposure to environmental factors such as UV radiation, moisture, and mechanical abrasion leads to the degradation of coatings, releasing microplastics into the environments. UV radiation causes the polymer chains in coatings to break, leading to embrittlement and fragmentation into smaller particles. Similarly, mechanical abrasion from wind, rain, or physical contact can wear down the coating surface, further contributing to the release of microplastics. These particles can then be transported by wind or water, spreading pollution across various ecosystems [34]. Routine maintenance, including sanding, scraping, and pressure washing of coated surfaces, can dislodge microplastic particles, which are then washed into stormwater systems and eventually reach oceans and rivers. For instance, when old paint layers are removed from buildings or ships, the process often generates significant amounts of microplastic debris. If not properly managed, these particles can enter the environment, exacerbating pollution levels. The process of removing old coatings, especially through abrasive methods, generates tremendous amounts of microplastic debris. Traditional methods such as sandblasting or high-pressure water jets can release a substantial amount of microplastics into the environment. Innovative technologies, such as the use of vacuum-assisted systems during paint removal, have been developed to capture these particles at the source, preventing their release into the environment [35]. Implementing such technologies can significantly reduce the environmental impact of coating removal processes. The release of microplastics from coatings occurs via various mechanisms, each contributing to environmental pollution. Understanding these pathways is imperative for developing strategies to mitigate their impact and protect ecosystems from further degradation and damage. 2.5.3. Marine Coatings and Oceanic Microplastic Pollution Marine coatings, especially antifouling paints applied to ship hulls, have become notable contributors to oceanic microplastic pollution. These coatings are designed to avert the accumulation of marine organisms, such as barnacles and algae, on the hulls of ships. By reducing biofouling, these paints help maintain fuel efficiency and avert the spread of invasive species. However, the very properties that make these coatings effective also lead to their degradation and the subsequent release of microplastics into the marine environment [36]. One primary mechanism of microplastic release is the cleaning process of ships. To maintain optimal performance, vessels undergo methodical cleaning to remove accumulated biofouling. Methods like hydroblasting, which use high-pressure water jets, can dislodge both the marine organisms and the underlying antifouling paint. A study focusing on hydroblasting a ship's hull stated that this process generated approximately 44.1 kg of paint particles, with 36.5 kg being smaller than 5 mm in size. Extrapolating this data suggests that globally, hydroblasting could release around 665.6 tons of plastics annually, with approximately 550.2 tons being in the form of microplastics [37]. Another significant source of microplastics is the wear and tear of coatings during a ship's operation. As vessels move through water, the constant friction causes gradual degradation of World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 235 the antifouling paint, leading to the release of microplastic particles. These particles can persist in the marine environment, contributing to the growing issue of microplastic pollution. The environmental impact of these microplastics is compounded by the presence of harmful additives in many antifouling paints. Substances such as copper, zinc, and various biocides are always incorporated to enhance the paint's effectiveness. When these paints degrade, these toxic substances can leach into the surrounding water, posing risks to marine life and ecosystems. Addressing the issue of microplastics from marine coatings requires a multifaceted approach. Implementing stricter regulations on the use of harmful additives in antifouling paints can help reduce their environmental impact. Additionally, adopting alternative cleaning methods that minimize paint degradation, such as ultrasonic cleaning or the application of biodegradable cleaning agents, can mitigate the release of microplastics [36, 37]. Furthermore, the development and adoption of more durable and environmentally friendly coatings can play a vital role in reducing the overall contribution of marine coatings to oceanic microplastic pollution. 2.5.4. Urban Sources of Paint-Related Microplastics In urban environments, paints and coatings contribute tremendously to microplastic pollution through numerous pathways, impacting both terrestrial and aquatic ecosystems. The degradation of road markings, weathering of building exteriors, infrastructure maintenance activities, and the removal of coatings all play pivotal roles in the release of microplastics into the environment. Road markings, essential for traffic safety and navigation, are composed of materials such as thermoplastics, epoxy resins, and glass beads. Over time, these markings undergo wear and tear due to vehicle abrasion and environmental factors like UV radiation and moisture. This degradation process results in the release of microplastic particles into the surrounding environment. Studies have estimated that the wear and tear of road markings can generate significant amounts of microplastics, contributing to urban pollution. For example, a study in Sweden estimated that the wear of road markings could release between 40 to 570 tonnes of microplastics annually, comparable to emissions from other sources like antifouling paints and artificial turf [38]. Building exteriors, particularly those exposed to outdoor elements, are coated with paints that can degrade over time due to UV exposure, moisture, and mechanical abrasion. This degradation leads to the release of microplastic particles into the environment. Research indicates that exterior paints, especially those used in construction and renovation, are significant sources of microplastics. These particles can be washed into stormwater systems during rainfall, eventually reaching rivers and oceans. In Europe, it's estimated that between 231,000 and 863,000 tonnes of microplastics enter the environment annually from paint waste, highlighting the considarable contribution of building exteriors to urban microplastic pollution [39]. Infrastructure maintenance activities, such as repainting and cleaning of urban structures, can generate microplastic debris if not properly managed. The process of sanding, scraping, or pressure washing surfaces to remove old coatings can release microplastic particles into the air and water. Without proper containment and disposal measures, these particles can enter stormwater systems, contributing to the overall microplastic load in urban environments [40]. The removal of coatings, particularly through abrasive methods such as sandblasting or highpressure washing, creates significant amounts of microplastic debris. If not properly managed, these particles can enter the environment, exacerbating pollution levels. Innovative technologies, such as the use of vacuum-assisted systems during paint removal, have been developed to capture these particles at the source, averting their release into the environment. Implementing such technologies can remarkably reduce the environmental impact of coating removal processes [41]. Urban sources of paint-related microplastics encircles a range of activities and materials, each contributing to the overall microplastic load in both terrestrial and aquatic environments. Addressing this issue requires a multifaceted approach, including the development of sustainable materials, implementation of effectual maintenance practices, and adoption of technologies that reduce the release of microplastics during coating application and removal. By comprehending and mitigating these sources, urban areas can move towards a more verifiable and environmentally friendly future [42]. 2.5.5. Environmental and Ecological Impacts of Paint-Related Microplastics The release of microplastics from paints and coatings has profound environmental and ecological implications, especially in marine ecosystems. These small particles infiltrate various habitats, leading to a cascade of detrimental effects on marine life, biodiversity, and ecosystem health. Marine organisms, ranging from microscopic plankton to large mammals, are increasingly ingesting microplastics, often mistaking them for food. This ingestion can lead to physical harm, such as internal abrasions and digestive blockages, which impair feeding efficiency and can result in malnutrition and stunted growth [43]. For instance, filter-feeding species like mussels and oysters accumulate microplastics in their gills, affecting their ability to filter feed and breathe properly. Moreover, these particles can leach toxic chemicals, including bisphenol A (BPA), phthalates, and persistent organic pollutants (POPs), into the tissues of marine organisms. Such chemical exposure can disrupt endocrine systems, cause cellular damage, and even lead to the development of tumors. As these contaminants move up the food chain, they pose increasing risks to higher trophic levels, including humans who consume seafood [43]. The accumulation of microplastics in marine environments also disrupts the structural and functional integrity of ecosystems. In coral reefs, microplastics can smother corals, blocking sunlight World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 236 essential for the symbiotic relationship between corals and their algal partners. This interference can lead to coral bleaching and increased susceptibility to diseases. Additionally, microplastics can alter the physical properties of sediments, affecting benthic organisms that rely on stable substrates for feeding and shelter. The presence of these particles can also change the optical properties of water, impacting the growth and distribution of phytoplankton, the foundation of marine food webs. Furthermore, microplastics serve as vectors for harmful bacteria and pathogens, facilitating their spread across marine environments. The surface of microplastics provides an ideal habitat for microbial colonization, potentially introducing diseases into marine food webs. This microbial hitchhiking can lead to the spread of invasive species and pathogens across ocean basins, disrupting local ecosystems and biodiversity patterns. The environmental and ecological impacts of paint-related microplastics are multifaceted, affecting marine organisms at various levels and disrupting the balance of marine ecosystems [44, 43]. Addressing this issue requires concerted efforts to reduce microplastic emissions, develop sustainable materials, and implement effective waste management practices to mitigate their release into the environment. 2.5.6. Mitigation Strategies of Paint-Related Microplastics Mitigating the environmental impact of microplastics from paints and coatings necessitates a multifaceted approach encompassing the development of alternative materials, the adoption of improved application techniques, the implementation of enhanced maintenance practices, and the establishment of regulatory measures. One of the primary strategies involves the development and utilization of alternative materials that do not contain microplastics or hazardous additives. This includes formulating coatings with biodegradable polymers, natural resins, or recycled materials to minimize the release of microplastics into the environment. For instance, research into sustainable polyurethane polymers derived from renewable resources such as soybean oil has shown promise in reducing the environmental footprint of coatings. Additionally, the incorporation of natural fibers in place of synthetic polymers can further contribute to reducing microplastic pollution [38, 45]. Improved application techniques are also crucial in minimizing the release of microplastics during the application process. Adopting methods that reduce overspray and spillage can prevent microplastic particles from being released into the air and subsequently settling into water bodies. For example, the use of precision equipment and controlled environments during the application of coatings can significantly decrease the amount of excess material that becomes airborne or enters stormwater systems [38, 39]. Enhanced maintenance practices play a vital role in reducing the degradation and removal of coatings, thereby limiting the release of microplastics. Implementing routine maintenance activities that minimize wear and tear on coated surfaces can extend the lifespan of coatings and reduce the frequency of repainting. Moreover, when maintenance is necessary, employing techniques that prevent the dislodging of microplastic particles like using vacuum-assisted systems during sanding or scraping, can notably reduce environmental impact. Regulatory measures are essential in guiding and enforcing the reduction of microplastics in paints and coatings [38, 46, 39]. Establishing regulations that limit the use of microplastics in coatings can help mitigate their environmental impact. For instance, the European Union has implemented restrictions on the intentional addition of synthetic polymer microparticles in products, including paints and coatings, to prevent their release into the environment. Such regulations encourage the industry to innovate and adopt more sustainable practices, ensuring that environmental considerations are integrated into product development and application processes [46]. Addressing the environmental impact of microplastics from paints and coatings requires a comprehensive approach that includes the development of alternative materials, the adoption of improved application techniques, the implementation of enhanced maintenance practices, and the establishment of regulatory measures. By integrating these strategies, it is possible to significantly reduce the release of microplastics into the environment, thereby mitigating their detrimental effects on ecosystems and human health. 2.5.7. Global Perspective of Paint-Related Microplastics The issue of microplastics originating from paints and coatings has emerged as a significant global environmental concern, contributing notably to marine pollution. These microplastics are released into the environment through various channels, including the application, wear, and removal of paints on surfaces such as roads, buildings, ships, and infrastructure. The degradation of these coatings over time results in the shedding of microplastic particles, which are then transported via wind, water runoff, and other means into oceans and waterways, causing threats to marine ecosystems and biodiversity [47]. International efforts are increasingly focusing on tackling this issue via comprehensive research, regulatory measures, and the development of sustainable alternatives. Organizations such as the United Nations Environment Programme (UNEP) have been instrumental in raising awareness and promoting actions to mitigate microplastic pollution. For instance, the UNEP has supported the development of international agreements and regional programs aimed at reducing marine plastic debris and microplastics, providing a foundation for establishing robust international rules on marine microplastic pollution at both global and regional levels [47]. In the European Union, significant strides have been made to regulate microplastics in paints and coatings. In 2023, the European Commission finalized a ban on synthetic polymer microparticles in mixtures, including paints, at concentrations of 0.01% or higher. This regulation aims to reduce the intentional addition of microplastics in products World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 243 the development of effective policies and interventions. Innovations like biodegradable sponges made from cotton and squid bone have shown the capacity to absorb up to 99.9% of microplastics in water, highlighting the potential of new materials in addressing this problem. Furthermore, real-time monitoring systems can track microplastic concentrations, informing timely responses and management strategies. A comprehensive approach involving technological innovation, sustainable design, public engagement, and scientific research is imperative in reducing microplastic pollution resulting from mechanical degradation. Concerted efforts across various sectors can lead to significant mitigations in microplastic contamination, safeguarding aquatic ecosystems and public health [71]. 3.2. Photodegradation Photodegradation, or photo-oxidation, is a remarkable environmental process contributing to the formation of microplastics. This mechanism involves the breakdown of plastic polymers when exposed to ultraviolet (UV) radiation from sunlight, resulting in the fragmentation of larger plastic items into smaller microplastic particles [72]. Mechanism of photodegradation of plastics to microplastics Photodegradation, also called photo-oxidation, is a notable environmental process contributing to the formation of microplastics. This mechanism involves the breakdown of plastic polymers when exposed to ultraviolet (UV) radiation from sunlight, resulting in the fragmentation of larger plastic items into smaller microplastic particles. The photodegradation process can be divided into many stages: initiation, propagation, branching, and termination [73]. • Initiation: The process begins when UV radiation is absorbed by the plastic polymer chains, particularly by chromophores like carbonyl groups present in the polymer structure. This energy absorption results to the formation of excited states in the polymer molecules, making them more reactive. As a result, chemical bonds within the polymer chains, particularly carbon–carbon (C–C) bonds, become weakened and prone to breaking. This bond scission generates free radicals, which are extremely reactive species that initiate the degradation process. • Propagation: As soon as free radicals are formed, they react with molecular oxygen present in the environment to produce reactive oxygen species (ROS) like peroxyl and alkoxyl radicals. These ROS further attack the polymer chains, resulting in the formation of hydroperoxides and other oxygenated functional groups. The presence of these functional groups, such as carbonyl and hydroxyl groups, indicates ongoing oxidative degradation of the polymer. This stage results in the gradual reduction of the polymer's molecular weight, making the material more brittle and susceptible to fragmentation. • Branching: In this stage, the degradation process becomes more complex. The hydroperoxides formed during propagation can decompose to generate additional free radicals, leading to chain branching. This branching creates a network of interconnected polymer chains, further reducing the material's structural integrity. The accumulation of these branched structures contributes to the formation of microplastics, as the material becomes increasingly fragmented and less cohesive. • Termination: The degradation process concludes when the free radicals recombine or disproportionate, resulting in the formation of stable, inert products. These products, which may include smaller polymer fragments, volatile organic compounds, and other degradation by-products, are typically less injurious than the original polymer. Nevertheless, the accumulation of these microplastic particles in the environment contributes significant ecological and health risks. Throughout these stages, various environmental factors can influence the rate and extent of photodegradation. For example, temperature, humidity, and the presence of other substances can accelerate or inhibit the degradation process. Additionally, the chemical structure of the polymer plays a vital role; polymers with aromatic groups or conjugated double bonds are more prone to photodegradation due to their ability to absorb UV radiation effectively. Understanding the mechanisms and stages of photodegradation is essential for developing strategies to reduce the formation of microplastics and their associated environmental impacts [73]. 3.2.1. Examples of Photodegradation in Different Plastics Different types of plastics exhibit varying susceptibilities and degradation pathways under UV exposure, influenced by their chemical structures and environmental conditions [74]. Expanded polystyrene (EPS), commonly used in packaging, is highly susceptible to photodegradation due to its unique foamed structure, composed of thin layers. A study found that EPS exposed to sunlight for 24 months produced approximately 6.7 × 10⁷ microand nanoparticles per square centimeter. The foamed structure of EPS makes it more vulnerable to fragmentation than bulk plastics. Under UV irradiation, the polymer chains in EPS undergo photo-oxidation, leading to the formation of free radicals that initiate the breakdown of the material into smaller particles. These microplastics can persist in the environment, contributing to pollution. Polypropylene (PP), another commonly used plastic, undergoes photodegradation through free radical World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 244 chain reactions when exposed to UV radiation. In marine environments, UV irradiation can produce free radicals that lead to the dissociation of carbon-carbon (C–C) and carbon-hydrogen (C–H) bonds from the polymer backbone, inducing chain scission and cross-linking reactions. This process contributes to the formation of microplastics in the marine environment. The presence of salts and dissolved organic matter in seawater can further accelerate the photodegradation of PP, leading to more rapid fragmentation and increased microplastic formation. Polylactic acid (PLA), a biodegradable plastic, degrades differently under UV exposure. The photodegradation of PLA occurs mainly through the cleavage of ester bonds, leading to the formation of smaller fragments. The degradation mechanism of PLA involves Norrish type I and II reactions, as well as radical oxidation reactions, resulting in the formation of microplastics in the marine environment. These processes are influenced by the chemical structure of PLA, which contains ester linkages that are susceptible to hydrolysis and photolysis under UV radiation. The photodegradation of different plastics involves complex chemical processes that lead to the formation of microplastics. The rate and extent of degradation depend on factors such as the chemical structure of the polymer, the presence of environmental factors like UV radiation and seawater, and the duration of exposure. Understanding these mechanisms is crucial for developing strategies to mitigate the environmental impact of microplastics and to design more sustainable materials [74]. 3.2.2. Factors Influencing Photodegradation of plastics The photodegradation of plastics is influenced by a combination of factors, including the color of the plastic, its polymer composition, and prevailing environmental conditions. Understanding these factors is essential for predicting the lifespan of plastic materials in various environments and for developing strategies to mitigate their environmental impact. By considering these variables, we can better address the challenges posed by plastic pollution and work towards more sustainable material usage and waste management practices [75]. 3.2.3. Color of Plastics The color of plastic materials significantly affects their susceptibility to photodegradation. Brightly colored plastics, such as red, blue, and green, tend to degrade more rapidly when exposed to environmental conditions [76]. This increased degradation rate is due to the presence of specific pigments that absorb ultraviolet (UV) radiation, leading to the formation of free radicals that initiate the breakdown of the polymer chains. For instance, a study found that polypropylene bottle tops with red, blue, and green pigments exhibited significant degradation over a three-year period, while black, white, and silver plastics remained largely unaffected. The black and white plastics often contain carbon black and titanium dioxide, respectively, which can act as stabilizers, reducing the rate of photodegradation. Conversely, the specific pigments in brightly colored plastics can enhance UV absorption, accelerating the degradation process [76]. 3.2.4. Polymer Composition The chemical structure of the polymer plays a pivotal role in determining its resistance to photodegradation. Polymers with aromatic groups or conjugated double bonds are more susceptible to UV-induced degradation due to their ability to absorb UV radiation effectively. For example, polyethylene terephthalate (PET) exhibits moderate UV resistance, while polyolefins like polypropylene (PP) and polyethylene (PE) are highly susceptible to photodegradation. The presence of ester bonds in PLA makes it more prone to hydrolytic degradation, especially under humid conditions. These structural characteristics influence how the polymer absorbs UV radiation and undergoes chemical transformations, leading to the formation of microplastics [77]. 3.2.5. Environmental Conditions Environmental factors such as temperature, humidity, and the presence of other substances can significantly influence the rate of photodegradation. Elevated temperatures can accelerate the degradation process by increasing the kinetic energy of molecules, leading to more frequent and energetic collisions [78]. For instance, studies have shown that the photodegradation of PET is more pronounced at higher temperatures, with the formation of carboxylic acids and other degradation products. Humidity also plays a crucial role, particularly in hydrolytic and biological degradation. The presence of water is essential for hydrolysis reactions and provides a conducive medium for microbial growth and enzyme activity. High humidity conditions promote the absorption of moisture into the polymer matrix, accelerating hydrolytic degradation. For example, in tropical regions with high humidity, polymers are more prone to rapid degradation. Conversely, in arid environments, the scarcity of moisture limits hydrolytic and biological degradation, thus preserving the integrity of polymers for a longer duration [78]. 3.2.6. Environmental Implications of photodegradation of plastics The fragmentation of plastics into microplastics through photodegradation has several environmental implications [79]. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 245 3.2.7. Marine Pollution Microplastics have become pervasive pollutants in marine environments, posing significant threats to aquatic life. Marine organisms, including fish, mollusks, and filter-feeding species like mussels, can ingest microplastics, leading to physical harm and potential toxicological effects [57]. For instance, a study conducted in West Bengal, India, found microplastics in over 80% of freshwater mussels analyzed, with potential risks of microplastics entering tissues like the gastrointestinal tract, potentially causing inflammation, oxidative stress, genetic damage, and even cell death [56, 57]. The ingestion of microplastics by marine organisms can disrupt their feeding and digestive processes, leading to reduced energy intake and potential starvation. Additionally, microplastics can accumulate in the food web, affecting predators higher up the chain, including humans who consume seafood. The persistence of microplastics in marine environments further exacerbates these issues, as they can remain in the ecosystem for extended periods, continuously impacting marine life [80]. 3.2.8. Soil Contamination Microplastics can also accumulate in soils, affecting soil health and potentially entering the food chain. The presence of microplastics in agricultural soils can alter soil properties such as structure, performance, and microbial diversity. For example, microplastics can affect soil density and porosity, which can impact water dynamics and soil aggregation, leading to reduced soil fertility and plant growth. Furthermore, microplastics in soil can serve as vectors for pathogens and antibiotic-resistant bacteria. Studies have shown that microplastics can harbor harmful microorganisms, which can be transferred to plants and subsequently enter the food chain. This poses significant risks to food safety and human health [79, 80]. 3.2.9. Human Health Risks The ingestion of microplastics by humans, either directly or through the food chain, raises concerns about potential health risks. Studies have found microplastics in various human tissues, including blood, semen, and breast milk, indicating widespread exposure [70]. Microplastics can cause inflammation, oxidative stress, and disturbances in lipid metabolism. They can also interfere with the intestinal microbiome, leading to gastrointestinal symptoms such as abdominal pain and bloating. Additionally, microplastics can carry environmental toxins like heavy metals and polycyclic aromatic hydrocarbons, which can enter the body via the gastrointestinal tract, causing nausea, vomiting, and abdominal pain. Furthermore, microplastics have been linked to respiratory symptoms when inhaled, including coughing, sneezing, and shortness of breath due to reduced blood oxygen levels, inflammation, damage, fatigue, and dizziness. Recent research also indicates that nano-sized plastics may cause mitochondrial damage in human respiratory cells [81]. The fragmentation of plastics into microplastics through photodegradation has far-reaching environmental implications. These tiny particles can accumulate in marine environments, affect soil health, and pose significant risks to human health. Addressing the issue of microplastics requires concerted efforts to reduce plastic usage, improve waste management practices, and develop materials that are less prone to degradation into microplastics [81]. 3.3. Chemical Degradation of Plastics into Microplastics Chemical degradation is a significant pathway through which plastics break down into microplastics in the environment. This process involves chemical reactions such as oxidation and hydrolysis, which are influenced by environmental factors like ultraviolet (UV) radiation, temperature, humidity, and the presence of reactive chemicals [82]. 3.3.1. Chemical Oxidation Oxidation is a primary mechanism in the chemical degradation of plastics, particularly polyolefins like polyethylene (PE) and polypropylene (PP). This process involves the reaction of polymer chains with oxygen, leading to the formation of free radicals and subsequent chain scission, which results in the breakdown of large polymer molecules into smaller fragments characteristic of microplastics [82, 83]. In the presence of oxygen and ultraviolet (UV) radiation, polymers undergo oxidative reactions that lead to the formation of free radicals. These free radicals can initiate chain scission, breaking the long polymer chains into shorter fragments. For example, when plastics like polyethylene (PE) or polypropylene (PP) are exposed to UV light, the energy from the UV photons can be absorbed by the polymer chains, weakening the chemical bonds that hold the chains together. This weakening leads to chain scission and the formation of smaller polymer fragments. Additionally, the presence of ozone (O₃) in the atmosphere can accelerate this process. Ozone reacts with unsaturated carbon-carbon (C=C) double bonds in the polymer structure, generating reactive oxygen species such as hydroxyl radicals (•OH), which further degrade the polymer chains into microplastic particles [83].The degradation of polyethylene in molecular oxygen between 150 and 250°C., in ozone-enriched O₂ between 20 and 109°C., and in fuming HNO₃ between 25 and 83°C. has been studied. The solid, liquid, and vapor products have been analyzed World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 246 by means of their infrared spectra. Kinetically, the O₂ oxidation reaction appears to be second order. The Elvish chemisorption equation ds/dt = ae^−αq was applied to the data and yielded comparable results. The kinetics were followed by pressure change and constant pressure measurements of oxygen uptake, and by the rate of increase of chemical structure image bands in the infrared spectra. The activation energy of the process was found to be 8–9 kcal. /Mole for the volumetric and manometric studies as well as for the ozone-catalyzed reaction, while the HNO₃ oxidation gave a 35.6 kcal. value. The presence of ozone (O₃) in the atmosphere can accelerate this process. Ozone reacts with unsaturated carbon-carbon (C=C) double bonds in the polymer structure, generating reactive oxygen species such as hydroxyl radicals (•OH), which further degrade the polymer chains into microplastic particles. 3.3.2. Hydrolysis Hydrolysis involves the chemical breakdown of polymers through reaction with water. This process is particularly significant for condensation polymers like polyesters (e.g., polyethylene terephthalate or PET) and polyamides. In the presence of water, hydrolysis can cleave ester or amide bonds in the polymer backbone, leading to the formation of smaller oligomers or monomers. For instance, PET can undergo hydrolytic degradation in aqueous environments, especially under acidic or basic conditions, resulting in the production of terephthalic acid and ethylene glycol. These smaller molecules can further degrade into microplastic particles [84]. 3.3.3. Environmental Factors Influencing Chemical Degradation The rate and extent of chemical degradation are influenced by various environmental factors. Temperature plays a crucial role; higher temperatures can accelerate chemical reactions, leading to faster degradation of plastics. For example, in marine environments, the combination of UV radiation and elevated temperatures can significantly enhance the chemical breakdown of plastics. Humidity also affects degradation; higher humidity levels can facilitate hydrolytic degradation by providing more water molecules for the reaction. Additionally, the presence of pollutants such as sulfur dioxide (SO₂) and nitrogen dioxide (NO₂) can contribute to the formation of reactive species like ozone, further promoting the chemical degradation of plastics [85]. 3.3.4. Implications of Chemical Degradation Chemical degradation not only leads to the formation of microplastics but also alters the chemical composition and physical properties of the plastic materials. The breakdown products can include a range of smaller organic molecules, some of which may be toxic or persistent in the environment. Moreover, the degradation process can increase the surface area and porosity of microplastics, enhancing their ability to adsorb other pollutants and potentially increasing their toxicity. This transformation underscores the complex environmental challenges posed by microplastics and highlights the need for comprehensive strategies to mitigate their impact. chemical degradation through oxidation and hydrolysis plays a pivotal role in the formation of microplastics. Understanding the mechanisms and influencing factors of this process is essential for developing effective measures to address microplastic pollution and its associated environmental risks [86]. 3.4. Biodegradation Biodegradation is a natural process wherein microorganisms such as bacteria and fungi break down biodegradable plastic polymers into smaller, less complex compounds. This process is particularly significant for plastics like polylactic acid (PLA), which are designed to be biodegradable. However, the efficiency and rate of biodegradation can vary based on several environmental factors, including temperature, humidity, and nutrient availability [87]. Microorganisms capable of degrading PLA typically produce specific enzymes that target the polymer's ester bonds. For instance, certain bacterial strains like Bacillus safensis have been isolated from environments such as landfill soils and shown to produce proteases and lipases that facilitate the breakdown of PLA. These enzymes hydrolyze the ester linkages in PLA, leading to the formation of lactic acid monomers and oligomers, which the microorganisms can then utilize as carbon sources. Studies have demonstrated that under optimal conditions, such as a temperature of 30°C and neutral pH, these bacteria can degrade PLA films by approximately 8% over a 30-day period. Scanning electron microscopy analyses reveal surface etching on the PLA films, indicating microbial activity [87]. Additionally, Fourier-transform infrared spectroscopy (FTIR) analyses show a decrease in the intensity of all absorption peaks, suggesting a reduction in the polymer's molecular weight and structural integrity. Fungal species also play a role in PLA biodegradation. For example, Amycolatopsis strains produce proteases that can degrade PLA films. Under laboratory conditions, these strains have been observed to degrade PLA films by approximately 60% within 14 days. The enzymatic activity of these fungi contributes to the breakdown of PLA into smaller fragments, which can then be further mineralized by other microorganisms. The rate of PLA biodegradation is significantly influenced by environmental conditions. High temperatures and humidity levels accelerate the hydrolysis of ester bonds in PLA, promoting microbial colonization and enzymatic activity. For instance, industrial composting facilities maintain elevated temperatures and moisture World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 247 levels that facilitate the rapid degradation of PLA [87]. In contrast, colder and drier environments, such as marine or desert settings, slow down the biodegradation process, leading to the persistence of PLA in these ecosystems. Nutrient availability also affects the efficiency of PLA biodegradation. Microorganisms require essential nutrients like nitrogen and phosphorus to produce the enzymes necessary for plastic degradation. In nutrient-limited environments, the production of these enzymes may be insufficient, hindering the biodegradation process. Supplementing the environment with these nutrients can enhance microbial activity and accelerate the breakdown of PLA. while biodegradation offers a promising method for mitigating plastic pollution, its effectiveness is contingent upon favorable environmental conditions and the presence of specific microorganisms capable of producing the requisite enzymes. Understanding and optimizing these factors are crucial for developing strategies to address plastic waste through biological means [87]. 4. Quantification Techniques Quantifying microplastics in environmental samples is a scrupulous process that involves various critical steps: sampling, separation, analysis, and data interpretation. Each step is designed to ensure appropriate identification, quantification, and characterization of microplastics, which are crucial for comprehending their distribution and impact. Figure 3 Various Quantification Techniques for Microplastics 4.1. Sampling Sampling serves as the keystone in the study of microplastics, laying the groundwork for successive analysis and interpretation. The integrity and dependability of research findings hinge on the diligent collection of representative samples from different environmental matrices, including water, sediment, soil, and biota. Each matrix presents outstanding challenges and necessitates tailored sampling methods to ensure precise representation and minimize contamination risks. In aquatic environments, water sampling is frequently conducted using nets or bottles. For example, the GR-91 rod dredger with a 300 cm³ bucket volume is employed to collect water samples from lakes and rivers. Similarly, the Ruttner bathometer, with a 5 dm³ volume, is utilized to sample water from particular depths. These methods ease the collection of large volumes of water, which are then filtered to isolate microplastics [88]. It's important to use clean, contamination-free equipment and to follow standardized protocols to avoid introducing external microplastics into the samples. For instance, in a study conducted in Kazakhstan, water samples were collected using metal buckets and bathometers, and filtration was carried out using Sefar polyamide mesh with a 100 µm mesh size to concentrate microplastics. Sediment sampling involves collecting surface layers, typically the top 5 cm, using metal tools such as shovels or corers. In marine environments, devices such as the Ekman grab sampler are used to obtain sediment samples. Once collected, sediments are commonly sieved and subjected to density separation techniques to isolate microplastics [89]. For instance, in a study in the Philippines, beach sediments were collected using metal shovels, dried, sieved, and then subjected to density separation to extract microplastics. Soil sampling requires meticulous consideration of spatial variability. Methods such as random, transect, or incremental sampling are employed to capture the heterogeneity of soil matrices. Soil cores are typically collected using hand augers or split spoon samplers. It's crucial to ensure that all samples are collected at consistent depths and that cross-contamination is minimized. For example, World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 248 the Interstate Technology & Regulatory Council (ITRC) recommends using non-plastic sample collection and storage containers and implementing accurate cleaning procedures for sampling equipment [90]. Sampling of biota involves capturing organisms from different trophic levels, like plankton, fish, or invertebrates. The sample size should be sufficient to provide statistically remarkable results, with recommendations suggesting at least 50 individuals per research unit. Biota samples are typically stored on ice or frozen at −20°C until analysis. It's imperative to handle these samples in clean air facilities to avoid contamination. For instance, a study published in Environmental Science & Technology emphasizes the importance of clean air conditions and thorough washing of materials and equipment when processing biota samples [88, 89, 90, 91]. To ensure the accuracy and reliability of microplastic analyses, strict contamination control measures must be implemented throughout the sampling process. This includes the application of clean, non-plastic equipment, thorough cleaning and rinsing of tools, and the use of appropriate storage containers. Additionally, procedural blanks should be run to assess contamination during sample processing. For example, in a study assessing microplastics in laundry effluents, field and laboratory blanks were collected and analyzed simultaneously with samples to evaluate potential contamination [92]. Effectual sampling is paramount in microplastic research. By employing appropriate sampling methods tailored to each environmental matrix and implementing rigorous contamination control measures, researchers can obtain dependable data that accurately reflects the presence and distribution of microplastics in the environment. 4.2. Separation This is the process of isolating microplastics from the collected samples. This step typically involves several techniques to concentrate and purify microplastics 4.2.1. Filtration Using filters with specific pore sizes to separate microplastics based on their size. Materials such as glass fiber, cellulose, or polytetrafluoroethylene are often used for filtration. The choice of filter material and pore size depends on the expected size range of microplastics and the analytical techniques to be adopted. 4.2.2. Density Separation Exploiting the difference in density between microplastics and the surrounding matrix. For instance, using salt solutions (e.g., sodium chloride or zinc chloride) to separate microplastics from sediments, as microplastics typically have a lower density and will float to the surface. This method is especially useful for sediment and soil samples [93]. 4.2.3. Chemical Digestion It involves using chemical agents to break down organic matter in the sample, leaving behind the microplastics. Often used chemicals include hydrogen peroxide (H₂O₂) for sediments and potassium hydroxide (KOH) or nitric acid (HNO₃) for biological samples. Care must be taken to avoid damaging the microplastics during this process. 4.3. Analysis Quantifying microplastics in environmental samples is a complex task that requires accurate and reliable analytical methods. The choice of technique depends on factors like the type of sample, the size and composition of microplastics, and the specific objectives of the study. Spectroscopic techniques, especially Fourier Transform Infrared (FTIR) and Raman spectroscopy, are extensively employed for microplastic identification and quantification. FTIR is effectual for detecting microplastics larger than 20 µm and can identify a broad range of polymers by analyzing their absorption of infrared light. Raman spectroscopy, on the other hand, offers higher spatial resolution and is capable of detecting smaller microplastics, sometimes down to a few micrometers. Both methods provide chemical fingerprints of microplastics, allowing for their identification and quantification within complex environmental matrices [94]. Another advanced technique is Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS), which thermally decomposes microplastics into smaller compounds that can be analyzed for identification and quantification. This method is specifically useful for analyzing a wide range of polymers and can be applied to different environmental samples, including soils and sediments. For high-throughput analysis, fluorescent dye staining combined with fluorescence microscopy and image analysis software offers a semi-automated approach to quantify microplastics. Dyes such as Nile Red bind to microplastics, enhancing their visibility under specific lighting conditions. This method is effectual for detecting smaller microplastics and can be coupled with software such as ImageJ to automate counting and categorization. Additionally, techniques like Laser Diffraction Particle Size Analysis and Dynamic Light Scattering are adopted to determine the size distribution of microplastics in environmental samples. These methods are specifically useful for analyzing nano plastics and understanding the particle size distribution, which is imperative for assessing potential environmental and health impacts. The quantification of microplastics involves a combination of sampling, World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 249 sample preparation, and analytical techniques tailored to the specific characteristics of the microplastics and the environmental matrix. The integration of different methods enhances the reliability and comprehensiveness of microplastic analyses, contributing to a better understanding of their prevalence and impact in the environment [94]. 4.4. Data Interpretation This involves analyzing the results to find out the concentration, distribution, and characteristics of microplastics in the samples. This step requires meticulous statistical analysis to account for potential biases and uncertainties introduced during sampling and analysis. The results are then compared with environmental standards or benchmarks to assess the potential impact of microplastics on ecosystems and human health [95]. Quantifying microplastics is a complex, multi-step process that requires meticulous planning and execution. Each step, from sampling to data interpretation, plays a pivotal role in ensuring accurate and reliable results. Standardized protocols and quality control measures are crucial to minimize errors and ensure the comparability of results across different studies [95]. 5. Environmental Impacts of Microplastics Microplastics have become prevalent pollutants impacting ecosystems across the globe. Their small size, durability, and common presence cause remarkable threats to both environmental and human health. Figure 4 Environmental Impacts of Microplastics 5.1. In marine environments Microplastics have infiltrated marine ecosystems worldwide, posing notable threats to marine life and the health of oceanic environments. These particles originate from different sources, including the breakdown of larger plastic debris, synthetic fibers from textiles, and microbeads in personal care products. Due to their small size and buoyancy, microplastics are easily taken in by a wide range of marine organisms, from microscopic plankton to large marine mammals [96]. Ingestion of microplastics can result in physical harm in marine organisms. For example, microplastics can accumulate in the digestive tracts of fish, resulting in internal injuries, blockages, and reduced feeding efficiency. This accumulation can result in malnutrition, stunted growth, and decreased reproductive success [96, 97]. In some cases, the ingestion of microplastics can pose false satiation, where organisms feel full despite not obtaining adequate nutrition. Additionally, sharp-edged microplastics may injure gill tissues and the intestinal tract, resulting in inflammation and increased susceptibility to infections. Beyond physical harm, microplastics can also introduce harmful substances into the marine food chain. These particles can absorb injurious chemicals from the surrounding water, like persistent organic pollutants (POPs), heavy metals, and pesticides. When marine organisms ingest microplastics, these toxic substances can enter their bodies, leading to bioaccumulation. As smaller organisms are consumed by larger predators, the concentration of these harmful substances increases up the food chain, a process known as biomagnification. This can have detrimental effects on marine biodiversity, impairing the health of entire ecosystems [97]. The impact of microplastics extends to different marine species. Plankton, the base of the marine food web, is especially vulnerable to microplastic pollution. Zooplankton can mistake microplastics for food, resulting in reduced nutritional intake and lower reproductive success. Since plankton is a primary food source for many marine species, including fish and whales, the impact of microplastics at this level can ripple through the entire food web, potentially affecting higher trophic levels. Fish species have demonstrated reduced energy reserves and stunted growth after consuming microplastics, which can affect their ability to survive and reproduce. Marine mammals, such as whales and World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 250 dolphins, have been found with microplastics in their stomachs, resulting in chronic and acute toxicity, including blockage of filtering apparatuses and internal injuries. The prevalent presence of microplastics in marine environments underscores the urgent need for combined global efforts to reduce their impact. Reducing plastic production and consumption, improving waste management practices, and developing technologies to remove existing microplastics from the environment are crucial steps in protecting marine ecosystems and the myriad species that depend on them [96, 97]. 5.2. In Terrestrial ecosystems Terrestrial ecosystems are also affected by microplastics. These particles can change soil structure and composition, affecting water retention and nutrient availability. Microplastics in the soil can disrupt the growth and development of plants by interfering with root systems and reducing seed germination rates. Additionally, they can affect soil-dwelling organisms, like earthworms, which play significant roles in soil aeration and nutrient cycling [98]. The presence of microplastics in soil can result in reduced agricultural productivity and compromised food security. Atmospheric deposition of microplastics is another emerging concern. Studies have detected microplastic particles in the air, which can be inhaled by humans and animals. These airborne particles can pose respiratory issues and may carry injurious substances into the lungs. The common presence of microplastics in the atmosphere indicates that they are a global pollutant, affecting even remote and pristine environments. The persistence of microplastics in the environment is a remarkable challenge. Due to their durability, they do not degrade easily and can accumulate over time, resulting in long-term environmental impacts [99]. This accumulation can result in the degradation of habitats, loss of biodiversity, and disruption of ecosystem services. Addressing the issue of microplastics requires concerted global efforts to mitigate plastic production and consumption, improve waste management practices, and develop technologies to remove existing microplastics from the environment. Microplastics represent a many-sided environmental issue with farreaching consequences. Their impact spans across marine and terrestrial ecosystems, the atmosphere, and human health. Reducing their effects necessitates a comprehensive approach involving policy changes, technological innovations, and public awareness to mitigate their prevalence and reduce their impacts on the environment and human health [98, 99]. 6. Toxicological Effects of Microplastics Microplastics can be harmful to both humans and the environment, with potential impacts on multiple organ systems and ecosystems. They can enter the body via ingestion, inhalation, and skin or dermal contact, leading to cellular toxicity and adverse effects on the digestive, respiratory, nervous, reproductive, and cardiovascular systems [100, 101,122]. Figure 5 Toxicological Effects of Microplastics (122 Modified) 6.1. Toxicity Mechanisms 6.1.1. Cellular Toxicity Microplastics can enter cells via endocytosis, resulting in cellular damage and death. For example, exposure to polystyrene microplastics has been demonstrated to cause mitochondrial dysfunction and necroptosis in chicken kidney cells [100]. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 251 6.1.2. Neurotoxicity There is growing evidence that microplastics can affect the nervous system. Inhalation of microplastics may lead to their accumulation in the respiratory tract and potential translocation across the blood-brain barrier, raising concerns about respiratory and neurological health effects [100, 101]. 6.1.3. Bioaccumulation and Biomagnification Microplastics can accumulate in tissues and move up the food chain. For instance, fish ingest microplastics, which can then be consumed by predators, resulting in bioaccumulation and potential biomagnification of toxins [100]. 6.1.4. Adsorption of Toxins Microplastics can adsorb injurious chemicals like heavy metals and pesticides, increasing their toxicity. These adsorbed toxins can then be released into organisms upon ingestion, leading to additional health risks [100]. 6.1.5. Oxidative Stress and Inflammation Microplastics can induce oxidative stress by generating reactive oxygen species (ROS), leading to inflammation. Studies have shown that exposure to microplastics activates immune responses, notably inducing the expression of proinflammatory cytokines such as IL-6 and TNF-α in various cell lines [100]. 6.1.6. Metabolic Disorders Exposure to microplastics has been linked to alterations in metabolism. In zebrafish, ingestion of microplastics resulted in changes to the gut microbiome and metabolome, resulting in oxidative stress and inflammation [100]. 6.1.7. Reproductive Issues Microplastics can adversely affect reproductive health. A study found that oral administration of microplastics to female mice resulted to reduced oocyte maturation and fertilization rates, as well as increased oxidative stress and DNA damage in oocytes. Moreover, microplastics have been detected in human ovarian follicular fluid, raising concerns about their impact on fertility [100]. 6.2. Exposure Pathways 6.2.1. Ingestion Microplastics are found in various food and water sources, including drinking water, seafood, and even table salt. Studies have reported microplastics in fish, mussels, and commercial salts, highlighting the prevalent nature of this contamination [102]. 6.2.2. Inhalation Airborne microplastics originate from sources like synthetic textiles, industrial emissions, and agricultural activities. Once inhaled, these particles may lodge in the lungs or enter the digestive system, posing health risks [103]. 6.2.3. Dermal Contact Microplastics can also be absorbed through the skin. Consumer products such as face creams and cosmetics may contain microplastics, increasing the risk of dermal exposure [104]. World Journal of Advanced Research and Reviews, 2025, 27(01), 228-262 252 Figure 6 Human Exposure Pathways to Microplastics(43 Modified) 6.3. Examples of Toxicity Microplastics have become a prevalent environmental contaminant, with growing evidence highlighting their detrimental effects on both animal and human health, as well as on ecosystems. In animal studies, microplastics have been demonstrated to cause remarkable health issues across various species. For example, research on fish, amphibians, and mammals’ states that microplastics can lead to liver damage, immune system dysfunction, and reproductive problems. In zebrafish, exposure to polystyrene nanoplastics has resulted in oxidative stress and liver damage, affecting their overall health and survival. Similarly, in mammals, studies have shown that microplastic exposure can impair ovarian function and alter hormone levels, resulting in reproductive toxicity [105]. These findings underscore the potential risks microplastics cause to animal health. Human studies, while still emerging, have begun to shed light on the potential health impacts of microplastics. Research has detected microplastics in human tissues, including the placenta, lungs, liver, and blood, raising concerns about their potential to pose health issues. For instance, a study by researchers from UC San Francisco reviewed over 3,000 studies and found strong evidence linking microplastic exposure to reproductive and immune system damage, with moderate evidence suggesting impacts on ovarian follicles, hormones, and lung function [106]. These findings suggest that microplastics may contribute to health problems such as infertility, colon cancer, and respiratory diseases. The environmental impacts of microplastics are also profound. In aquatic ecosystems, microplastics can harm organisms by affecting their growth, reproduction, and overall health. For example, studies have shown that microplastics can reduce the reproductive capacity of freshwater zooplankton, resulting in population declines. Additionally, microplastics can disrupt the food chain by affecting the health of primary producers such as algae, which are essential for the survival of higher trophic levels. Furthermore, the ingestion of microplastics by marine organisms like fish and turtles can lead to digestive tract blockages, reduced stomach capacity, and even mortality [107]. Concerns about microplastic exposure are especially heightened regarding long-term health effects, as the chronic consequences are still being investigated. The accumulation of microplastics in human tissues over time may lead to persistent health issues, including chronic inflammation and organ damage. Moreover, susceptible populations such as infants and children may be more vulnerable to the harmful effects of microplastics due to their developing bodies and higher exposure levels. For instance, studies have detected microplastics in human placentas, suggesting potential risks to fetal development [108]. Ecosystem health is also at risk as a result to microplastic pollution. The presence of microplastics in various habitats can disrupt ecological balance, affecting biodiversity and the functioning of ecosystems. For example, the accumulation of microplastics in marine environments can lead to the decrease of species that are crucial for ecosystem stability. Additionally, microplastics can serve as vectors for toxic chemicals, further exacerbating their impact on ecosystems. 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