15 The Global Distribution & Impacts of Microplastics
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Ever since plastic waste has become spread worldwide because of ever-increasing industrialization, microplastics have followed suit. Microplastics have now been detected in virtually every facet of the planet, from urban environments to the most remote ecosystems. Their concentrations have continually been increasing in the soil, atmosphere, and water. The widespread distribution of microplastics can largely be attributed to their lightweight nature, allowing them to become airborne and travel long distances by wind or being easily swept away by water currents. As discussed previously, human-production of plastic has exponentially increased in the last century which certainly doesn’t help with the ever-increasing concentrations of microplastics in various environments (Yang et al., 2025). This subsection of the chapter will focus specifically on the worldwide impacts of microplastics in the way they are distributed throughout the worldwide environment, both indoors and outdoors, the ways in which global policy has evolved regarding microplastics, and the mitigation strategies that have arisen as more awareness of microplastics has been raised.
Worldwide Distribution and Environmental Fate
As introduced earlier in this chapter, microplastics can be categorized as either primary or secondary, depending on how they are produced. However, beyond their type, it is also important to consider the specific sources through which these particles enter the environment. These sources are broadly divided into point and non point sources. Point sources release microplastics from identifiable, localized origins, whereas nonpoint sources discharge microplastics diffusely across larger areas, making them harder to trace and manage.
Common point sources include industrial and municipal wastewater outfalls, stormwater drains, and emissions from industrial smokestacks. In cases where outfalls are untreated, microplastics are directly discharged into nearby rivers and streams, where they are subsequently transported to lakes, estuaries, and oceans. In countries with developed wastewater treatment infrastructure, approximately 72% of microplastics are removed through primary treatment, and up to 94% can be eliminated with tertiary treatment (ITRC, 2021). However, this level of removal is not universal. Developing countries, which may lack advanced treatment facilities, often experience higher microplastic discharge into surface waters used by local populations and ecosystems.
Even when microplastics are removed during treatment, they do not disappear. These particles are often concentrated in biosolids, which are either incinerated, landfilled, or applied to soils as amendments intended to alter soil characteristics. During drying or land application, wind can easily disperse microplastics from biosolids into the surrounding environment. Other notable point sources include discarded or lost material from commercial shipping, passenger vessels, and aquaculture facilities (ITRC, 2021).
In contrast, nonpoint sources are more difficult to identify and manage due to their diffuse nature. These include stormwater runoff, atmospheric deposition, and the application of biosolids on agricultural land. Additional contributors include tire wear particles, erosion of synthetic materials, and residues from urban and household waste. Airborne microplastics, which are an emerging area of concern, frequently originate from synthetic textiles, abrasion of vehicle tires, and the resuspension of city dust. Because nonpoint sources can stem from nearly any landscape or weather-driven process, their mitigation poses a significant global challenge (ITRC, 2021).
Microplastics have been detected in water sources across the globe, originating from a range of both point and nonpoint sources. Nearly all surface water bodies are contaminated with microplastics, not only through direct discharges but also due to atmospheric deposition, which allows particles to reach remote and otherwise unaffected locations. Although microplastics are far more prevalent in surface waters, they have also been found in groundwater—albeit in more limited quantities. Research on microplastics in groundwater is still emerging, but studies in countries such as the United States, Germany, and South Africa confirm their presence in subsurface water systems. A study conducted in northern China by Jingyun Shi and colleagues revealed that microplastic concentrations in groundwater are highest near sewage treatment plants, landfills, and agricultural areas, especially those involved in vegetable production. This same study identified a link between microplastics and antibiotics, showing that microplastics can bind to antibiotic molecules through hydrogen bonding, hydrophobic interactions, van der Waals forces, and electrostatic interactions. This binding reduces the degradation of antibiotics in both soil and water environments. According to separate studies by Samuel Panno, Viviana Re, and their teams, microplastics can enter groundwater systems through fractures, losing streams, soil crevices, conduits, and karstic features such as branch-work caves. Smaller microplastic particles are particularly prone to migrate deeper into the subsurface (ITRC, 2021).
Determining the exact quantities of microplastic contamination across different global regions remains challenging. However, studies on marine environments around the world provide insight into the scale of contamination faced by each area. Since plastics became widely used across societies, microplastics have been detected in every ocean—including remote regions such as the Arctic, Antarctic, deep sea, and mid-ocean islands. For example, a study of California’s coastal waters estimated that nearly two billion microplastic fragments were discharged by two rivers in less than three days. In the San Francisco Bay, microplastic concentrations ranged from 15,000 to 20,000 particles per square kilometer. Similarly, at an intertidal site near a shipbreaking yard in India, microplastic concentrations reached 81 ppm (mg/L). Research conducted in Arctic waters near Svalbard, Norway, reported particle concentrations ranging from 0 to 1.31 particles per cubic meter in southern waters and 0 to 11.5 particles per cubic meter southwest of the site (Auta et al., 2017). As the presence of microplastics continues to grow, numerous studies are underway to better quantify global concentrations and distributions. Figure # illustrates a global map of microplastic distribution in kilograms per square kilometer, showing the highest concentration within the North Pacific Gyre, located off the coast of California. Other regions of the world’s oceans display similar levels of contamination, suggesting widespread and persistent microplastic pollution across marine environments.
Later sections of this chapter will explore in greater detail the impacts of microplastics on the world’s oceans and aquatic ecosystems, as well as their occurrence in drinking water, soil, and food sources. For now, however, the following subsection will specifically examine the presence of microplastics in both atmospheric and indoor air environments, along with their associated effects.