EIACP Programme Centre on Climate Change & Public Health

Understanding Microplastics: A Growing Health Concern

Microplastics are small particles of synthetic polymers and plastic materials measuring less than 5 millimeters (0.2 inches). The term "microplastic" was first introduced in a 2004 publication to describe microscopic plastic debris (~20 µm in diameter). These tiny particles can originate from two main sources: they may be intentionally incorporated into products such as cosmetics and cleaning agents or result from the decomposition of larger plastic items. Once released into the environment, microplastics are challenging to degrade and may pose risks to both wildlife and human health.

Classification of Microplastics: Primary and Secondary

Microplastics exist in various forms and sizes, typically ranging from micrometers to millimeters. They are classified into primary and secondary microplastics based on their origin.

Primary Microplastics

These are intentionally manufactured micro-sized plastic particles used in industrial and consumer products. Examples include:

• Microbeads: Found in cosmetics and personal care items, these tiny plastic spheres often enter water systems.
• Microfibers: Released from synthetic textiles, carpets, and personal care products, they are a major contributor to microfiber pollution.
• Resin Pellets (Nurdles): Raw materials for plastic production that can spill into the environment, harming aquatic life.

Primary microplastics are a growing concern due to their widespread presence and potential to adsorb toxic chemicals, affecting marine organisms and human health.

Secondary Microplastics

These result from the breakdown of larger plastic items like bags, bottles, and packaging due to mechanical, chemical, and UV exposure. They form fragments, fibers, and microbeads, contributing significantly to environmental pollution.

Once released, secondary microplastics contaminate air, soil, and water, traveling through wind and water currents. Marine organisms often ingest them, leading to health complications and ecosystem imbalances. These microplastics pose significant ecological and health risks, highlighting the urgent need for better plastic waste management.

Figure 1: Classification of Microplastics: Primary and Secondary Categories Source: E.C. Emenike et al. (2023)

Properties of Microplastics:

The likelihood of microplastic absorption by organisms increases as particle size decreases. Uptake is further influenced by factors such as hydrophobicity, surface charge, and functionalization. Particles with low hydrophobicity and a negative surface charge tend to be absorbed more readily.

Additionally, microplastics are believed to develop a protein corona, a layer of biomolecules that accumulates on their surface. This corona significantly affects how microplastics are taken up and transported within the body.

Structurally, microplastics are composed of carbon and hydrogen atoms bound together in polymer chains.

Common Sources of Microplastics:

·         Textiles: Around 70% of modern textiles are made from synthetic materials, which shed significant amounts of microplastics into the environment.

·         Cosmetics & Personal Care Products: Many personal care items still contain intentionally added microplastics, such as glitter and microbeads found in facial and body scrubs.

·         Fishing & Aquaculture: Microplastics are introduced into marine environments through various means, including:

·         Unfiltered gray water discharge from ships.

·         Breakdown of lost or discarded fishing gear.

·         Marine paints and coatings used on vessels.

·         Single-use plastic waste from fishing and aquaculture operations.

·         Agriculture: Microplastics enter the soil through multiple agricultural practices, such as:

·         The extensive use of crop films.

·         Irrigation pipes.

·         Nutrient tablets.

·         Seed coatings.

·      Traffic: Sources of microplastics from roadways include tire wear, road markings, and road debris.

·      Plastics Processing: Plastic pellets, used as raw materials in manufacturing new and recycled plastic products, are a significant source of microplastic pollution.

Plastic Pollution:

Plastic production has surged from 2.3 million tons in 1950 to 460 million tons annually by 2022.

Microplastic emissions are estimated to range between 10 and 40 million tons per year, with projections suggesting this could double by 2040.

The vast majority of plastics today are derived from fossil fuels, and approximately 0.5% of plastic waste ultimately reaches the ocean.

The top five plastic waste-producing countries include China (60 million tons), the United States (42 million tons), Brazil (11.3 million tons), India (9.46 million tons), and Japan (9.0 million tons)

How does microplastic get into the environment?

Microplastics enter the environment through multiple pathways. Plastic waste from residential areas, landfills, and sewage treatment plants breaks down into microplastics and nanoplastics, which disperse into the air, water, and soil. These particles accumulate in terrestrial ecosystems through animal feces, contaminated crops, and livestock exposure. In aquatic ecosystems, microplastics settle in sediments, contaminate sea salt, and are ingested by marine organisms, eventually entering the human food chain through seafood consumption. Their presence in the atmosphere further contributes to widespread environmental pollution.

Figure 2: Routes of Human Exposure to Microplastics   Source: Yue Li et al. (2023)

Impact of microplastics on Human Health:

·         Microplastics can enter the human body through contaminated food, polluted air, and drinking water, particularly from plastic bottles. They have also been found in various food items, including sea salt, honey, sugar, beer, and mineral water.

·         It is commonly stated that humans consume, inhale, and absorb about 5 grams of microplastics weekly. A recent study estimated that adults ingest up to 121,000 microplastic particles annually through air, food, and beverages.

·         Since microplastics can reach multiple organs, their ingestion may cause oxidative stress, potentially leading to inflammation, allergic reactions, and, in severe cases, cancer or even death. While inhaled microplastics can be excreted by mucociliary cleansing, some may settle in the lungs or enter the bloodstream.

·         Currently, there is no definitive guideline on the threshold level of microplastic intake that poses a significant health risk to humans.

·         These plastic particles have been identified in various human biological samples, including the lungs, breast milk, liver, spleen, placenta, blood, sputum, colon, saliva, feces, urine, testes, and semen. However, they have not been detected in the kidneys or lungs of stillborn infants.

      Figure 3: Health impacts of Microplastics Source: Yue Li et al. (2023)

Potential Health Effects of Microplastics

• Respiratory Issues: Breathing in airborne microplastics can lead to respiratory problems such as coughing, wheezing, and aggravated asthma. The severity of health effects depends on the size and persistence of these fibers. Smaller, thinner fibers can penetrate deep into the lungs, where they are difficult to clear and may cause lung inflammation and cellular toxicity. Workers in industries like synthetic textiles and plastic manufacturing face a higher risk of developing pulmonary diseases due to prolonged exposure. Studies have detected synthetic fibers in the lung tissues of affected workers, with some experiencing progressive lung function decline and respiratory failure even after leaving the workplace. Additionally, microplastics in urban air can carry harmful pollutants such as toxic metals and polycyclic aromatic hydrocarbons (PAHs), further increasing lung damage and genetic mutations.
• Cardiovascular Issues: Microplastic exposure has been associated with cardiovascular conditions like hypertension, atherosclerosis, and heart rhythm disorders. These particles can induce oxidative stress, inflammation, and endothelial dysfunction, disrupting normal heart function. Research on animal models shows that microplastics reduce cell viability, alter gene expression, and trigger immune responses. In rats, microplastics have been linked to heart damage, fibrosis, and metabolic changes, while mice exposed to polystyrene microplastics exhibited weight gain, insulin resistance, and elevated blood glucose levels. Human studies also suggest that microplastics accumulate in thrombi, raising concerns about their role in cardiovascular diseases. However, some findings indicate that exposure to polystyrene microplastics at realistic blood concentrations may pose a lower cardiovascular risk in humans, highlighting the need for further investigation.
• Gastrointestinal Issues: Consuming microplastics through contaminated food and water can cause digestive problems such as inflammation, irritable bowel syndrome, and gut microbiota imbalance. Microplastics accumulate in the digestive system, leading to irritation and potential blockages. Research shows they can alter gut microbial composition, increase oxidative stress, and disrupt immune function. Studies on zebrafish and human intestinal cells indicate that microplastics can damage intestinal lining, trigger inflammation, and elevate reactive oxygen species (ROS) production. Prolonged exposure may contribute to conditions like inflammatory bowel disease (IBD), with higher microplastic concentrations found in affected individuals.
• Endocrine Disruption: Microplastics contain and absorb endocrine-disrupting chemicals (EDCs) such as bisphenol A (BPA), phthalates, and nonylphenol. These substances interfere with hormonal balance, affecting reproduction, development, and overall health. Studies on zebrafish and other marine species show that microplastics can enhance the bioaccumulation of toxic substances, leading to reproductive dysfunction and hormonal imbalances. Research also suggests that microplastics contribute to endocrine disruption in fish, with observed alterations in gene expression and reproductive abnormalities. However, further studies are needed to understand the extent of chemical leaching and its direct impact on human health.
• Skin Irritation: While direct skin exposure to microplastics has not been definitively linked to adverse health effects, there is potential for irritation, redness, itching, and inflammation. Certain microplastics have abrasive properties that may disrupt the skin’s natural barrier or clog pores, leading to discomfort. Additionally, chemical additives and contaminants in microplastics could further contribute to irritation. Although studies on rats have shown no significant skin or eye irritation from prolonged exposure to polypropylene (PP) microplastics, the possibility of such effects in humans cannot be dismissed.
• Allergic Reactions: Microplastics may also trigger allergic responses by activating the immune system, leading to symptoms such as swelling, hives, or, in rare cases, severe reactions like anaphylaxis. Individuals with pre-existing sensitivities or allergies may be more prone to these effects. Some research suggests that high concentrations of PP microplastics can stimulate immune responses and increase hypersensitivity. However, studies on polystyrene (PS) particles indicate that while they may not directly cause allergic reactions, they can induce early-stage inflammation.
• Cellular & DNA Damage: Nano-sized plastics may enter cells, causing oxidative stress, apoptosis, and DNA damage, raising concerns about long-term health risks.
• Microplastics can pose several health risks, including direct physical harm as foreign particles, exposure to toxic additives (such as plasticizers and PFAS), and the absorption of environmental pollutants like heavy metals. These tiny plastic particles can enter tissues, the bloodstream, and even internal organs and cells.

Figure 4: Adverse Health Effects of Microplastic Exposure Source: Yongjin Lee et al. (2023), doi: 10.3349/ymj.2023.0048

Widespread Presence and Potential Health Risks of Microplastics in Organisms and Humans

Microplastics have been detected in various organisms, including aquatic animals, pets, plants, and humans. Fish and mussels from different regions contain microplastics, with fibers being the most commonly ingested type. Studies have also found microplastics in the intestines, stomach, liver, and muscles of coastal animals, as well as in pet feces. Additionally, plants like rice and algae can absorb microplastics, which has potential applications for environmental cleanup. In humans, while microplastics are primarily excreted through the gastrointestinal and biliary tracts, they have also been found in blood, indicating systemic distribution. They have been detected in multiple organs, including the liver, spleen, colon, lungs, placenta, and breastmilk, with the highest concentrations in the colon and liver. Infants are particularly vulnerable, as studies show higher levels of microplastics in their feces compared to adults. Microplastics in the placenta raise concerns about intergenerational effects, potentially influencing fetal development and increasing the risk of chronic diseases later in life.

Solutions:

One approach to managing plastic waste is incineration for energy production, known as energy recovery. However, recycling is considered a more effective solution. Raising awareness through recycling campaigns and strengthening infrastructure and investments in recycling programs could help address microplastic contamination. Some experts suggest advancing recycling technologies to process smaller plastics, thereby reducing the need for new plastic production. Another potential solution is biodegradation, where microorganisms break down synthetic polymers using enzymes. This process allows plastics to be converted into energy and carbon sources. Additionally, microbes could be utilized in wastewater treatment to minimize the release of microplastics into the environment.

References:

1.      Thompson, R. C., Courtene-Jones, W., Boucher, J., Pahl, S., Raubenheimer, K., & Koelmans, A. A. (2024). Twenty years of microplastic pollution research-what have we learned?. Science (New York, N.Y.), 386(6720), eadl2746. https://doi.org/10.1126/science.adl2746

2.      Winiarska, E., Jutel, M., & Zemelka-Wiacek, M. (2024). The potential impact of nano- and microplastics on human health: Understanding human health risks. Environmental research, 251(Pt 2), 118535. https://doi.org/10.1016/j.envres.2024.118535

3.      Li, Y., Tao, L., Wang, Q., Wang, F., Li, G., & Song, M. (2023). Potential Health Impact of Microplastics: A Review of Environmental Distribution, Human Exposure, and Toxic Effects. Environment & health (Washington, D.C.), 1(4), 249–257. https://doi.org/10.1021/envhealth.3c00052