Microplastics

Microplastics are defined as synthetic polymer particles smaller than 5 millimeters in size, either shaped or unshaped, and insoluble in water. These materials, typically derived from petrochemicals, consist of solid particles formed from a mixture of polymers and various functional additives.

History

The term “microplastic” was first used in a 1968 report published by the United States Air Force Materials Laboratory to describe particles formed due to the deformation of plastic materials exposed to high stress.^【1】

The scientific community began recognizing microplastics as an environmental issue in the 1970s following observations in marine environments. The presence of extremely small plastic particles on ocean surfaces and coastal sediments was first reported during this period. However, the modern conceptualization of the term and its adoption as a standard in scientific literature emerged in the early 2000s through the research of marine biologist Richard Charles Thompson and his colleagues. Thompson’s 2004 study demonstrated that plastics in marine environments were not limited to large debris but also included tiny particles with significant ecological impacts, thereby establishing the current usage of the term “microplastic.”^【2】

Since the 2010s, microplastics have become one of the key issues in global environmental policies and scientific research. Studies conducted during this period have shown that microplastics are not only present in oceans but also in freshwater systems, soil, the atmosphere, and even polar regions. Simultaneously, findings of microplastics detected in human tissues have shifted the focus of the issue beyond environmental science into the center of public health research.

Today, microplastics have become a multidisciplinary research subject shared by numerous scientific fields including chemistry, biology, environmental engineering, toxicology, and medicine. The historical development of research has shown a progression from viewing these particles solely as a material science concern to understanding them as a complex form of pollution with global environmental and biological impacts.

Classification and Sources of Formation

Microplastics are classified into two main categories based on their release sources and formation processes: primary and secondary microplastics. Primary microplastics are particles intentionally manufactured at microscopic scales for industrial purposes. This group includes microbeads used as abrasives or volume enhancers in cosmetics and personal care products, industrial pellets used as raw material in plastic production, and materials used in sandblasting equipment. These particles are typically discharged directly into aquatic environments through wastewater systems after use.

Secondary microplastics result from the fragmentation of larger plastic materials—known as macroplastics—such as plastic bottles, fishing nets, plastic bags, and vehicle tires under environmental influences. Ultraviolet (UV) radiation from sunlight, mechanical abrasion from wave action, and biological degradation processes cause large plastic items to break down over time into microplastics. For example, particles shed from vehicle tires due to friction with roads or microfibers released from synthetic textiles during washing in laundry machines are among the primary sources of secondary microplastics.

Environmental Distribution and Transport Mechanisms

Microplastics can spread over vast geographic areas via wind, surface runoff, and wastewater. Terrestrial environments transition to aquatic ecosystems through critical intermediaries such as domestic wastewater treatment plants and solid waste disposal sites. Due to limitations in current filtration technologies, wastewater treatment facilities fail to fully capture micro-sized particles, resulting in their discharge into receiving environments such as seas, lakes, and rivers. Similarly, microplastics generated from the degradation of plastic waste at landfill sites infiltrate groundwater and surface water sources through leachate, contributing to contamination.

Domestic wastewater treatment plants are considered one of the largest and most critical sources for transporting terrestrial microplastics into aquatic ecosystems. Microplastics from households enter these facilities via sewer systems. The main sources of these microplastics are microfibers shed from synthetic clothing during laundry and primary microplastics such as microbeads found in personal care products. Current wastewater treatment technologies are designed to remove organic pollutants and lack the capacity to fully capture microplastic particles. Studies have detected varying concentrations of microplastics in effluent water, with even low levels per liter becoming significant when considering that these facilities discharge millions of liters daily into the environment. Microplastics removed from water during treatment settle into sludge; when this sludge is applied to agricultural land as fertilizer, microplastics enter farmland soils and subsequently contaminate groundwater.

Research has demonstrated that microplastics can reach from the Mariana Trench, the deepest point on Earth, to the summit of Mount Everest. In aquatic environments, these particles can remain suspended in the water column or accumulate in sediment layers. For instance, sediment analyses in semi-enclosed coastal systems such as Küçükçekmece Lagoon have revealed high concentrations of microplastic accumulation.

Ecological Impacts and the Food Chain

Due to their small size, microplastics are frequently mistaken for food by aquatic organisms. This affects a wide range of species across ecosystems, from zooplankton to fish, crustaceans, seabirds, and mollusks. Ingestion of microplastics can lead to direct physiological and behavioral effects, including digestive tract blockages, inflammation and tissue damage, disruption of growth and development, reduced reproductive capacity, and even death under high exposure conditions. Particularly in seabirds, observations have revealed a fibrotic disease called “plasticosis” caused by ingested plastics, which results in permanent damage to the lungs and digestive systems.

Microplastics do not only cause physical harm; they also pose serious risks as chemical carriers. Plastic surfaces can adsorb heavy metals, pesticides, polycyclic aromatic hydrocarbons (PAHs), and other toxic organic compounds from the environment. These chemicals can be transported along the food chain with microplastics, accumulating in consumer organisms and leading to biomagnification. This increases toxic effects in predator species such as fish, seabirds, and marine mammals. Additionally, pathogens and antibiotic-resistant bacteria can colonize the surfaces of microplastics, facilitating the spread of diseases across ecosystems and potentially impacting human health.

Microplastics reaching higher trophic levels through the food chain can negatively affect biological diversity beyond threatening ecosystem health. For example, declines in plankton populations due to microplastic exposure can disrupt food web balances, impacting fish stocks and food sources for seabirds. These cascading effects may compromise the functionality of ecosystem services in the long term and reduce the sustainability of aquatic systems.^【3】

Effects on Human Health

Humans are exposed to microplastics through inhalation, ingestion, and skin contact. Given their pervasive presence in nearly every aspect of human life, entry into the human body has become unavoidable. Through ingestion via food and water, humans consume microplastics from seafood, salt, sugar, honey, apples, carrots, cabbage, broccoli, and pears. In regions bordering seas and oceans, seafood consumption is a major exposure source; drinking water may also contain microplastics. Through inhalation, microplastics suspended in airborne dust and particles—particularly in cities with high air pollution—can reach the lungs. Although less emphasized, it is also believed that microplastics may enter the body through the skin.

Once inside the body, microplastics do not remain confined to entry points but can be transported via the circulatory system to various organs. Particles smaller than 100 nanometers have the potential to penetrate cell membranes and disseminate throughout the body. Studies have detected microplastics in human blood, lung tissue, and heart tissue; for instance, PET and polyurethane plastics have been identified in tissues of patients undergoing heart surgery. A 2021 study found microplastic particles in human placenta, demonstrating that plastics can reach unborn babies.^【4】

Research on the effects of microplastics on human health is ongoing, but current findings indicate various risks. Laboratory studies have shown that microplastics can trigger allergic reactions and even cell death in human cells. Moreover, microplastics can act as chemical carriers by containing harmful additives used in their production and adsorbing toxic chemicals and pathogens from the environment, thereby transporting them into the human body. The presence of microplastics in the placenta raises concerns for fetal development and health, as these particles may have the potential to cause developmental abnormalities.

Tea Bags and Nanoplastic Exposure

Although tea bags are widely preferred for their convenience in modern consumption habits, they have become a significant area of research due to the release of microplastic and nanoplastic particles when exposed to hot water. Many commercial tea bag polymers—particularly polypropylene, nylon-6, and some “cellulose-like” materials—have been shown to release millions to billions of micro- and nanoplastic particles when heated. Experiments conducted at brewing temperatures around 95 °C confirmed that these particles enter the liquid, leading consumers to unknowingly ingest large quantities of plastic.

A 2019 study by Italian researchers reported that steeping a single plastic tea bag releases approximately 11.6 billion microplastic and 3.1 billion nanoplastic particles. These initial findings marked a turning point in examining tea bag materials as direct sources of contamination. More recent studies have confirmed similar microplastic release patterns with different commercial materials; for example, polypropylene tea bags were found to release about 1.2 billion particles per milliliter, while nylon and cellulose fibers released particles at lower rates.^【5】

The health effects of these particles remain a focus of scientific research. Laboratory studies have demonstrated that these particles can be absorbed by human intestinal cells and have the potential to enter the bloodstream; some findings even suggest that nanoplastic particles may reach the cell nucleus. However, risk assessment agencies emphasize that current data remain insufficient regarding both human exposure levels and toxicological outcomes. For instance, Germany’s Federal Institute for Risk Assessment noted that although the particle release from tea bags is extremely high, there is currently no conclusive evidence that they directly harm human health; however, research gaps necessitate further investigation.

A quantitative analysis published in 2024 reported detecting between 80 and 1,288 micron-scale microplastic particles and nanoplastic subunits per tea bag; the study also showed that simple methods such as pre-rinsing can significantly reduce microplastic quantities.

It has been suggested that the amount of microplastics ingested from tea bags may be higher than from other food sources, and that polymer contamination in different sweet tea varieties may originate from environmental and production processes. These findings highlight the urgent need for regulatory policies and standards regarding food safety, human health, and the use of plastic materials in products that come into contact with food.

The World Health Organization (WHO) states that more research is needed to fully understand and manage the effects of microplastics in drinking water.

Common Environments of Microplastics

Microplastics have been detected in various environmental settings globally. In aquatic ecosystems, they are not only found in surface waters but also throughout the entire water column and in sediment layers. For example, microplastic particles have been identified even in the deep ocean trenches such as the Mariana Trench.

Studies have also found microplastics to be widespread in freshwater systems; analyses of lakes and rivers consistently detect particles in both sediment and water samples. Furthermore, microplastics have been identified in groundwater and tap water, demonstrating that plastic particles are not fully removed during water treatment processes.

Microplastics can also be found in the atmosphere. Plastic particles transported by wind and air currents can disperse between terrestrial and marine ecosystems. Additionally, microplastic presence has been detected in remote areas such as polar regions, high mountain peaks, and glaciers. Microplastics accumulating in soils and sediments form long-term environmental records.

Research has demonstrated that microplastics are not confined to specific regions but exhibit widespread distribution across terrestrial, aquatic, and atmospheric systems.

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