The effects of microplastics on human health are a subject of ongoing study. These extremely small plastic particles originate from larger plastics and have been detected in high volumes in human biological samples, air, water, and food.Vethaak, A. D., & Legler, J. (2021). Microplastics and human health. Science, 371(6530), 672-674. This has raised concerns about the long-term impacts on human health.
Plastic particles smaller than 5mm are considered microplastics (MPs). Particles smaller than 1μm are nanoplastics (NP), which are too small to be seen by the human eye. Nanoplastics remain less studied than larger plastic debris, and their long-term health impacts are still being investigated. Given their minute size, nanoplastics can penetrate biological barriers and accumulate in human tissues, raising questions about potential health effects.
Micro- and nanoplastics (MNPs) have been detected in multiple organs and tissues, as well as human feces, urine, breastmilk, and neonatal meconium, suggesting widespread exposure and absorption.Schwabl, P., Köppel, S., Königshofer, P., Bucsics, T., Trauner, M., Reiberger, T., & Liebmann, B. (2019). Detection of various microplastics in human stool: a prospective case series. Annals of internal medicine, 171(7), 453-457. Larger MNPs are thought to be filtered out by normal bodily defenses, such as by mucus in the nose or by coughing. However, "ultrafine" particles are able to enter the circulatory system through the lungs. Additionally, when MNPs are introduced directly into the bloodstream, such as during medical treatment, they bypass our natural defenses.
Although experimental studies within cell cultures and animals have shown possible biological effects, human evidence remains limited, and long-term health risks are still being researched. A 2024 systematic review of human and animal observational studies concluded that MNPs are "suspected" to be harmful to human reproductive, respiratory, and digestive health.
The World Health Organization has acknowledged growing concerns, but note that standardized measurement methods and risks have not been established, calling for further research and improved management of plastic throughout its life-cycle.
Routes of exposure and bioaccumulation
The major pathways of human exposure to MNPs are inhalation, ingestion and dermal contact, with bioaccumulation varying based on particle size, composition, and physicochemical characteristics. Research suggests that MNPs above 150 μm typically remain confined to tissues and do not enter systemic circulation, whereas particles below 200 nm can breach cellular and tissue barriers, potentially reaching the bloodstream and other organs.Revel, M., Châtel, A., & Mouneyrac, C. (2018). Micro (nano) plastics: a threat to human health?. Current Opinion in Environmental Science & Health, 1, 17-23. This diversity in bioaccumulation pathways underscores the widespread yet nuanced risks of MNP exposure to human health.
These findings collectively suggest that MNPs may accumulate in multiple organ systems depending on the exposure route, potentially leading to long-term health consequences as their presence in human tissues builds up over time.
Inhalation Airborne MNPs originate from urban dust, rubber tires, household plastic items, and synthetic fibers from textiles. It is also theorized that particles that have entered our waterways can become suspended in the air via wave action, as well as via the spreading of wastewater treatment sludge on agricultural fields. Once inhaled, these particles may become lodged in the lungs or, through mucociliary clearance, be ingested and enter the digestive system. Airborne microplastics have been detected in urban atmospheres, with reports showing a fallout of 29–280 particles per square meter per day on an urban rooftop, underscoring the potential for routine exposure. Annual inhalation exposure rates vary, with some studies estimating individuals inhale up to 68,000 particles each year.
Children are at higher risk of exposure to MNPs by inhalation. When compared to adults, children have less efficient nasal filtering, are more typically mouth breathers, and breathe more air per unit of body mass. This makes them more susceptible to air pollutants of all kinds.
Ingestion
Ingestion is one of the primary pathways of MNP exposure due to the omnipresence of these particles in food, beverages, and drinking water. Studies show that MNPs are detected in a variety of consumables, including drinking water,"World Health Organization (WHO). Information sheet: Microplastics in drinking-water". World Health Organization (WHO). Information sheet: Microplastics in drinking-water. beer, honey, sugar, table salt, and even airborne particles that settle on food. Indirect ingestion also occurs via toothpaste, face wash, scrubs,Kau, B. (2018). "For the first time, study confirms presence of microplastics in Indian cosmetics". downtoearth.org.Leslie, HA (2014). "Review of microplastics in cosmetics". IVM Institute for Environmental Studies. '476': 1–33. and soap."Plastic Cosmetics: Are We Polluting the Environment Through our Personal Care?". United Nations Environment Programme.
Marine products are particularly concerning sources of ingestion-related exposure due to the accumulation of MNPs in aquatic environments. Fish, bivalves, and other seafood are frequently contaminated with MNPs that are ingested through water and food and build up through the process of bioaccumulation. Humans consuming these animals are thus directly exposed to microplastics embedded in tissue; for instance, humans eat the entire soft tissue of bivalves, along with their digestive systems, which increases the direct transfer of MNPs. In a study along the Mediterranean coast of Turkey, 1822 MNPs were extracted from the stomachs and intestines of 1337 fish specimens, with fibers accounting for 70% of these particles.
Contamination is further compounded by plastic packaging and storage materials, which can leach MNPs over time, leading to additional ingestion from common foods and drinks.Aslam, S., Khurram, A., Hussain, R., Qadir, A., & Ahmad, S. R. (2023). Sources, distribution, and incipient threats of polymeric microplastic released from food storage plastic materials. Environmental Monitoring and Assessment, 195(6), 638. Concerns have also been raised about exposure due to plastic cookware and utensils, with one study estimating that using plastic cookware may introduce up to 4,900 microplastics into homecooked food each year. Studies have shown that drinking water from plastic bottles has significantly greater detectable plastic content than tap water.
Fecal sample analyses estimate a daily intake of approximately 203–332 MNPs, translating to an annual ingestion rate of around 39,000–52,000 particles.Zhang, S., Wang, J., Yan, P., Hao, X., Xu, B., Wang, W., & Aurangzeib, M. (2021). Non-biodegradable microplastics in soils: a brief review and challenge. Journal of Hazardous Materials, 409, 124525. This suggests that daily MNP exposure from food and drink may be substantial, with significant implications for gastrointestinal and systemic health. Estimates of dietary exposure vary across studies due to differences in sampling and detection methods, contributing to uncertainty about typical intake levels.
Maternal exposure
Recent studies have shown the presence of microplastics in breast milk, often leading to exposures in very young children. While it has already been established that chemicals such as flame retardants and pesticides have been detected in breast milk, knowledge about microplastics is limited in comparison. A 2022 study detected microplastics in 26 of 34 breast milk samples, with particles ranging from 2 to 12μm in size, raising concerns about infant exposure during critical developmental windows.Santoro, A., Marino, M., Vandenberg, L. N., Szychlinska, M. A., Lamparelli, E. P., Scalia, F., ... & Meccariello, R. (2024). PLASTAMINATION: Outcomes on the Central Nervous System and Reproduction. Current Neuropharmacology, 22(11), 1870-1898.Kopatz, V., Wen, K., Kovács, T., Keimowitz, A. S., Pichler, V., Widder, J., ... & Kenner, L. (2023). Micro-and nanoplastics breach the blood–brain barrier (BBB): Biomolecular corona's role revealed. Nanomaterials, 13(8), 1404. No safe or harmful exposure level for microplastics has been established, and exposure to MNPs during early developmental stages has raised questions about possible developmental effects or other health issues later in life.
Additionally, breast pumps and breastmilk storage bags are frequently made of plastic. Freezing liquid in a plastic container and then heating it up (the "freeze-thaw cycle") has been shown to increase the presence of microplastics. Similar results have been seen from heating plastic reusable food containers in a microwave, showing the increased release of MNPs. It is not recommended that frozen breastmilk ever be thawed in a microwave.Canadian Agency for Drugs and Technologies in Health (June 2016). "Storage, Handling, and Administration of Expressed Human Breast Milk: A Review of Guidelines". National Library of Medicine. PMID 27336107. Retrieved 28 April 2024.
Medical exposure Though rarer; intravenous therapies such as IV bags, injections, and similar, may introduce thousands or millions of micro and nano plastics directly to the bloodstream, including not only solid, but also liquid PDMS plastics lubricants. This may enhance microplastic exposure due to the direct nature of the delivery, which bypasses bodily defences. Saline IVs have been found to introduce 1,600–8,000 microparticles per mL and 4-73 million nanoparticles per mL in IV, with high levels persisting post-filtration. Even blood collection needles appear to introduce plastic to the bloodstream, despite the fact they take fluids rather than injecting them. As such general exposure from disposable plastic medical equipment appears quite high.
Skin contact
Dermal exposure to MNPs occurs through contact with contaminated media like soil, water, and personal care products, including facial and body scrubs containing MNPs as exfoliants. Although the skin generally acts as a barrier, conditions such as skin lesions or high exposure environments may allow for enhanced absorption of MNPs, particularly nanoplastics, which can penetrate the stratum corneum. Furthermore, workers handling production of textiles, garments, fabric, and other fiber products are constantly exposed through inhalation and direct dermal contact. This highlights the need for further research into the effects MNPs have on human health, especially on industrial workers who have higher rates of exposure.
Studies on dermal exposure highlight the potential for these particles to enter systemic circulation, especially if the skin barrier is disrupted by wounds or conditions that increase permeability, like pores such as sweat glands and hair follicles.
Occupational exposure
Workplace exposure can be at a high concentration for the duration of a shift, and thus short-term, whereas exposure outside of work is at low concentration and long-term. For instance, the concentration of worker exposure from extrusion 3D printers is orders of magnitude higher than the general population (e.g., 4×1010 particles per cubic meter [m3] versus 50 particles per m3 in the general environment).
The main route of workplace exposure is acute inhalation. Plastics are extensively used in the construction and renovation industry. Airborne microplastic dust is produced during renovation, building, bridge and road reconstruction. High chronic exposure to aerosolized MNPs also occurs in the synthetic textile industry, the flocking industry, and the plastics industry, especially in vinyl chloride and polyvinyl chloride (PVC) manufacturers.