Plastic particles smaller than 5mm are considered microplastics (MPs), while nanoplastics (NPs) are defined as particles smaller than 1mm. These particles originate from larger plastics and have been detected in high volumes in human biological samples, air, water, and food. The presence of microplastics in our environment has raised concerns about the long-term impacts on human health. Nanoplastics remain less studied than larger plastic debris, including their long-term health impacts which are still being investigated. Given their minute size, nanoplastics can penetrate biological barriers and accumulate in human tissues, raising questions about potential health effects.
Plastics continue to accumulate in landfills and oceans, leading to pollution that negatively affects both human and animal health. Microplastics and nanoplastics are now ubiquitous, infiltrating our food chain and water supplies. Studies indicate that humans ingest significant amounts of microplastics daily through food (especially seafood) and inhalation, with estimates of annual exposure varying widely depending on the methodology.
Most microplastic is filtered out by normal bodily defenses, such as mucus. However, when microplastics are introduced directly into the bloodstream, such as during medical treatment, they bypass these defenses. The presence of microplastics in human feces suggests widespread exposure and absorption.
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. Public health agencies have acknowledged the growing concern, but note that standardized measurement methods and risks have not been established.
The major pathways of human exposure to micro- and nanoplastics (MNPs) are ingestion, inhalation, and dermal contact, with bioaccumulation varying based on particle size, composition, and physicochemical characteristics. Research suggests that MNPs above 150 üm 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. This diversity in bioaccumulation pathways underscores the widespread yet nuanced risks of MNP exposure to human health.
Plastics are extensively used in the construction and renovation industry. Airborne microplastic dust is produced during renovation, building, bridge and road reconstruction projects and the use of power tools.
Airborne MNPs originate from urban dust, synthetic fibers from textiles, rubber tires, and household plastic items. These airborne particles may become suspended in the air due to wave action in aquatic environments or the spread of wastewater treatment sludge on agricultural fields. Once inhaled, these particles may lodge 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 29âÂÂ280 particles per square meter per day on an urban rooftop, underscoring the potential for routine exposure. Annual inhalation exposure rates estimates vary, with studies highlighting the significant contributions from synthetic textiles and urban dust sources.
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 becomes more pervasive over time.
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, beer, honey, sugar, table salt, and even airborne particles that settle on food. Indirect ingestion includes toothpaste, face wash, scrubs, and soap.
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 ingested through water and food, and humans consuming these animals are thus directly exposed to microplastics embedded in tissue. The entire soft tissue of bivalves, for instance, is eaten by humans, which increases the direct transfer of MNPs. In a study along the Mediterranean coast of Turkey, 1822 microplastics 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. Fecal sample analyses estimate a daily intake of approximately 203âÂÂ332 MNPs, translating to an annual ingestion rate of around 39,000âÂÂ52,000 particles. 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.
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 smaller than 5 mm in 75% of analyzed breast milk samples, raising concerns about infant exposure during critical developmental windows.
Exposure during developmental stages have raised questions about possible developmental effects or other issues later in life. While these detected levels were not above the currently established thresholds for unsafe levels, they show another possible route for microplastic ingestion. Studies have shown that pumping milk, freezing it in plastic bags, then subsequently heating it up will increase the contamination of microplastics in the milk. Similar results have been seen from heating plastic reusable food containers in a microwave, showing the release of both micro- and nanoplastics. Studies have shown that drinking water from plastic bottles has significantly greater detectable plastic content than tap water.
These findings suggest that breastfeeding has prompted further investigation into potential endocrine-related effects, which could have lasting effects on growth and development.
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 1,600âÂÂ8,000 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.
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.
Incidental generation of MNPs is mechanical or environmental degradation or industrial processes such as plastic manufacturing (heating and chemical condensation) and intentional generation of MNPs occur during 3D printing.
The main route of workplace exposure is acute inhalation. Workplace exposure can be high concentration and lasting the duration of a shift and thus short-term whereas exposure outside of work is at low concentration and long-term. The concentration of worker exposure is orders of magnitude higher than the general population (e.g., 4ÃÂ10<sup>10</sup> particles per cubic meter [m<sup>3</sup>] from extrusion 3D printers versus 50 particles per m<sup>3</sup> in the general environment).
High chronic exposure to aerosolized MNPs occur in the synthetic textile industry, the flocking industry, and the plastics industry, especially in vinyl chloride and polyvinyl chloride manufacturers.
The potential health impacts of MPs vary based on factors, such as their particle sizes, shape, exposure time, chemical composition (enriched with heavy metals, polycyclic aromatic hydrocarbons [PAHs], etc.), surface properties, and associated contaminants.
Experimental and observational studies in mammals have reported a range of biological responses to micro and nanoplastic exposure. It is shown that MPs and NPs exposure have the following adverse effects:
Despite growing concern and evidence, most epidemiologic studies have focused on characterizing exposures. Epidemiological studies directly linking MPs to adverse health effects in humans remain yet limited and research is ongoing to determine the full extent of potential harm caused by MPs and their long-term impact on human health.
Although bodies of research have examined the potential health effects of micro- and nanoplastics, scientific uncertainties still remain. Much of the existing evidence is coming from laboratory experiments and animal models, which may not directly reflect human exposure. Differences in particle size, shape, and chemical additives complicate comparisons across studies.
A major limitation involves the lack of standardized methods for detecting plus quantifying nanoplastics in environmental and biological samples. Variability in sampling techniques influences inconsistent data records. Accurately measuring nanoplastics is technically challenging because of their small size and different properties.
Experimental studies often exceed typical environmental exposure levels when exposing animals or cells to concentrations. This makes it difficult to determine if these same effects will happen at lower, more realistic levels of exposure. No threshold in which nanoplastics begin to significantly affect human health has been established.
Public health agencies have acknowledged. that there is a need for further research on assessing exposure levels and possible public health implications. Ongoing research aims to clarify exposure pathways, biological interactions, and risks.
The risk of sample contamination during collection, differences in whether studies report particle counts versus mass concentrations, and difficulty differentiating the effects of microplastics and the effects off absorbed pollutants.
MPs have been found in bloodstreams, and other locations of the body.
As of April 2024, there is no established NIOSH Recommended Exposure Limit (REL) for MNPs due to limited data on exposure levels to adverse health effects, the absence of standardization to characterize the heterogeneity of MNPs by chemical composition and morphology, and difficulty in measuring airborne MNPs. Thus, safety measures focus on the hierarchy of controls for nanomaterials with good industrial hygiene to implement source emission control with local exhaust ventilation, air filtration, and non-ventilating engineering controls such as substitution with less hazardous materials, administrative controls, Personal Protective Equipment (PPE) for skin, and respiratory protection.
Research from the U.S. National Institute of Occupational Safety and Health (NIOSH) Nanotechnology Research Center (NTRC) show local exhaust ventilation and High Efficiency Particulate Air (HEPA) filtration to be effective mitigation to theoretically filter 99.97% of nanoparticles down to 0.3 microns.