14 Introduction to Microplastics
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Introduction
There are very few artificially created materials more abundant than plastic in the daily life of an average person in the modern era. This abundance has been born of plastic’s low cost of creation, durability, and versatility in usage. However, it is also common knowledge that plastics exponentially increased widespread usage throughout the last century has led to significant environmental challenges. To give you an idea for the scale of the problem of plastic, the amount of plastic produced worldwide is projected to reach 33 billion tonnes by 2050 (Enyoh et al., 2020). Among the most concerning issues regarding plastics is microplastic pollution. Microplastics are solid plastic particles that are smaller than 5 millimeters, insoluble in water, non-degradable, and persist in the environment for long periods of time. They have been detected in many aquatic species along with drinking water and numerous foods/food products such as salt, honey, and seafood. These particles originate from primary sources, meaning they are intentionally produced by industry, and secondary sources, where larger plastic debris degrades into smaller fragments over time (Ziani et al., 2023).
Historical Context and Recognition of Microplastics
Synthetic polymers first appeared in the late 19th century, specifically around the 1860s, which in turn led to the creation of plastics as we know them today decades later. It is important to note that all plastics are synthetic polymers, but not all synthetic polymers are plastics. It was not until after World War II that the boom of plastics really began to take place. Plastic has since become one of the most widespread materials since its initial creation as a phenol-formaldehyde resin intended to improve human living conditions and support the industrial boom. Nowadays, plastic has become a severe problem to the environment and safety of the planet (Ziani et al., 2023). For purposes of illustrating the scale of the problem to the reader, a graph of the increasing amounts and types of plastic wastes can be seen in figure 1.1.
Plastic is now present in air, water, and soil, largely due to its widespread use in food packaging for prod
ucts like dairy, meat, fish, and beverages. When food comes into contact with plastic packaging, chemical transfer occurs, potentially compromising food quality and safety. Microplastics have been detected in various environments, including soil, surface water, coastal sediments, beach sand, and even rain and snow. Poor waste management and excessive plastic use have led to massive plastic waste accumulation, making plastic pollution a major environmental issue. The primary topic of this chapter, microplastics, are defined as small, synthetic, non-degradable plastic particles, and are persistent pollutants that are easily released and remain in the environment for long periods. These particles contribute to food chain contamination, carrying harmful chemicals that impact aquatic ecosystems. Marine organisms, such as fish and crustaceans, are exposed to microplastics and suffer negative effects on their feeding, growth, and reproduction. Microplastics are largely created from the degradation of plastic waste. As a result, humans are exposed to microplastic pollution through seafood consumption (Ziani et al., 2023).
The term ‘microplastics’ first appeared in reports in 2004, where it was used to describe fragments of plastic approximately 20 micrometers in diameter. These early reports referred to truly microscopic plastic particles but did not provide a specific definition for microplastics which was not created until 2008. In that year, the United States National Oceanographic and Atmospheric Agency (NOAA) hosted the first internation workshop on microplastics in the state of Washington where the current definition of microplastics was crafted, being plastic particles smaller than 5 millimeters. With this current definition, microplastics on the larger scale are visible to the human eye but the definition also encompasses the original definition of truly microscopic plastic particles. “Microplastics” is now essentially an umbrella term that covers many different particle shapes, sizes, polymer types, and physical/chemical properties. Although,
no international consensus has been reached regarding the definition of microplastics and varies country to country based on size and material (Lee et al., 2023). As such, they are considered to be a different category from the primary microbeads that are commonly used for ecotoxicity testing (Ziani et al., 2023).
Definition and Classification of Microplastics
As stated previously, microplastics are defined as plastic particles that are less than 5 millimeters (mm) in diameter. In spite of their small size, microplastic particles exhibit wide ranges in form, physical composition, and chemical properties which can influence their behavior within the environmental and biological systems in which they invade (Ziani et al., 2023). The following list will describe microplastics by their origin, physical appearance, and chemical compositions:
Classification by Origin
Microplastics are typically characterized into two categories based on their origin and a tertiary subcategory worth mentioning all on its own:
Primary Microplastics: These are intentionally manufactured microplastics for use in commercial or industrial product. They are released into the environment upon their usage or rather the moment they split off from their item of purpose. Common examples of primary microplastics include:
- Cosmetics
- Cleaning products
- Industrial abrasives used in sandblasting
- Artificial turf
- Fishing nets
Secondary Microplastics: These are not intentionally produced but the result of their creation remains the same. These microplastics are created from the fragmentation of larger plastic debris into increasingly smaller sizes. Fragmentation occurs mainly due to the extensive oxidation of plastics under exposure to solar UV radiation. Upon the weakening of the plastic caused by radiation, it takes very little mechanical stress to separate the plastic into fragments. This process continually occurs until the plastic fragments become small enough to be considered microplastics (Andrady, 2022). Common sources of secondary microplastics include
- Fragmentation of plastic bags, bottles, and packaging materials
- Tire wear particles from road friction
- Paint and coating residues
Nano plastics: These are the result of excessive fragmentation of already existing microplastics. They can be generated from the fragmentation of both primary and secondary microplastics released into the environment. Nano plastics are particularly dangerous to both environmental and biological systems because they cannot be seen with the naked eye at a diameter of less than 1 micrometer and are thus incredibly easy to be ingested by all living organisms they encounter. Due to their small size, they can become airborne and are most notably present in densely populated urban areas and are deemed highly reactive and abundant as a result (Ziani et al., 2023).
Classification by Shape and Color
Microplastics can come in a variety of shapes and colors. Color wise, microplastics can come in all colors in the spectrum based on the specific materials/pigments they are composed of. After all, plastic is not a set entity in terms of material makeup. Studies conducted in China have sho
wn that white, black, and transparent were the most common colors, constituting 56% of the total microplastics, with 48% of that percentage being black. These studies concluded that the
color of microplastics determined based on an initial visual observation can be useful for tracing their origins (Yang et al., 2025). Color has also been found to be associated with preferential treatment for ingestion by marine organisms based on what specifically visually appeals to certain species. Shape wise, the physical forms of microplastics influences their ability to move through the environment and be ingested by organisms (Alvarez et al. 2019). Examples of common shapes in which microplastics can appear are:
- Fibers: thin, thread-like strands primarily shed from synthetic textiles
- Fragments: Irregularly shaped pieces from broken-down plastic objects
- Beads: Spherical or oval particles commonly found in cosmetics and industrial applications
- Foams: Porous microplastics originating from materials like polystyrene
- Films: Thin, sheet-like plastics derived from degraded plastic bags or wrappers
Classification by Chemical Composition
Microplastics are composed of various types of synthetic polymers, each with unique chemical properties and degradation behavior. Chemical composition varies with the microplastic’s origin as fragmentation/degradation of a plastic bag may be different than say, a water bottle or fishing net. Some of the most common compounds which compose microplastics are indicated below (Ivleva, 2021).
- Polyethylene (PE): commonly used in plastic bags, bottles, and containers
- Polystyrene (PS): common in disposable cups, cutlery, and insulation materials
- Polypropylene (PP): common in food packaging, textiles, and medical applications
- Polyvinyl Chloride (PVC): becoming increasingly more common in pipes as cast iron is being phased out. Also used in flooring and synthetic leather.
- Polyethylene Terephthalate (PET): frequently used in water bottles and synthetic fibers
- Chemical additives (not the primary material in composition): plasticizers, flame retardants, and colorants. Additives can easily leach into the environment and pose additional risks.
Figure 1.5. Chemical structure of common microplastic polymers. (Source: ResearchGate)
The dominant atmospheric microplastic polymers at different locations varies but, it is known that the most produced polymer types are polypropylene at 19.3%, low-density polyethylene at 17.5%, high-density polyethylene at 12.3%, polyvinyl chloride at 10.2%, and so on and so forth. In seawater, the dominant polymer type was polyethylene followed by polystyrene. As of right now, there is not a clear explanation regarding the variability of microplastic chemical composition in different facets of the environments, but it is desirable to determine the dominant polymers within those facets for purposes of studying the effects/reactions those specific chemicals may cause (Yang et al., 2025).
The Concern with Microplastics
In recent years, microplastics have emerged as a growing environmental and public health concern, posing risks to both humans and wildlife. One of the primary issues with microplastics is their small size, which makes them easily ingested and allows them to accumulate within food chains, persisting in the environment for years due to their resistance to biodegradation. Microplastics enter living organisms through inhalation, ingestion, and dermal contact, making exposure nearly unavoidable. Their microscopic size also makes them impractical to remove once released into the environment (Lee et al., 2023).
Observational studies on marine organisms have shown that microplastic ingestion, particularly at high concentrations, leads to internal organ abnormalities and toxic effects. The ecotoxicity of microplastics can be attributed to their polymer composition and the chemical additives within them. While the full extent of their effects on human health remains unclear, studies indicate that ultrafine microplastics (under 100 nanometers) can be absorbed and transported to multiple organs within the human body. Research conducted by Prata in South Korea found that airborne microplastics are present in the atmosphere, raising concerns about their potential role in respiratory and cardiovascular diseases, particularly in vulnerable populations. Similarly, a study by Chopi on marine zooplankton demonstrated that smaller microplastics tend to be more toxic, emphasizing the dangers of bioaccumulation and long-term exposure (Lee et al., 2023). Additionally, it has been observed that atmospheric microplastics are generally smaller tha aquatic, sediment, and soil microplastics (Yang et al., 2025).
Beyond their physical presence, microplastics act as carriers of persistent organic pollutants and bacteria, increasing their potential toxicity when ingested. With rising concentrations of microplastics detected in water, food, and living environments, concerns are growing about their impact on human health and ecosystems. Furthermore, the lack of precise data on their prevalence and the absence of standardized risk assessment methods complicates efforts to fully understand and mitigate their dangers. Addressing the microplastic crisis will require comprehensive research, improved waste management strategies, and global regulatory efforts (Lee et al., 2023).
Scope and Organization of the Chapter
This chapter will explore various aspects of the growing issue of microplastic pollution and its far-reaching consequences on the environment and human society. The next section will examine the global impacts of microplastics, including their effects on public health, economic systems, and airborne pollution, as well as broader environmental and regulatory challenges. Regulations that have since been put in place regarding the global impact of microplastics will also be detailed. Following this, the chapter will delve into the widespread presence of microplastics in the world’s oceans, highlighting their role in marine ecosystem disruption and the potential risks they pose to biodiversity. Additionally, the chapter will address microplastics in drinking water, emphasizing their potential health hazards and exposure pathways for human populations. Lastly, the final section will explore the causes and consequences of microplastic contamination in food and soil, shedding light on the infiltration of these particles into agricultural systems and food chains.