Microplastics and human health

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 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. 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. Inhalation Airborne MNPs originate from urban dust, synthetic fibers from textiles, rubber tires, and household plastic items. 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. beer, honey, sugar, table salt, and even airborne particles that settle on food. 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. 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. 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 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. 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. 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 ==

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. The concentration of worker exposure is orders of magnitude higher than the general population (e.g., 4×1010 particles per cubic meter [m3] from extrusion 3D printers versus 50 particles per m3 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. Manufacturing and processing of plastic • 3D printing, such as commercial extrusion printing and multi-jet fusion printing with thermoplastics and resin, emits MNPs and volatile organic compounds into the ambient workplace air. For extrusion printing, Acrylonitrile butadiene styrene (ABS) filaments emit more MNPs than Polylactic acid (PLA) filaments. • Nylon flocking is the process of applying, cutting, sanding, and machining of nylon polymers on surfaces where dust emission peaks during air blowing flocked surfaces. • Coating utensils and cookware: polytetrafluoroethylene, and high energy or heat processing of plastic products (Bello et al. 2010; Walter et al., 2015). • Dust generation occurs in a wide range of settings from composite material machining, drilling, hand-held grinding, and sanding of nanotube-containing composites, and sanding of dental composites, and cutting PVC piping and plastics. • PVC and plastic production produces PVC dust with mortality confirmed among vinyl and PVC workers after reanalysis of data, and coronary artery disease and cancer death among vinyl chloride exposed workers. • Rubber chemical manufacturing impacting mortality among these workers. Environmental and mechanical degradation of plastic • Carpet and synthetic fibers: indoor air contains high concentrations of degraded synthetic fibers with potential exposure by office workers and custodial staff. Settled dust is ingested by adults and particularly children. Recycling facilities and landfills serve as reservoirs of particulates workers may potentially be exposed to. Medical plastic • Face masks and respirators: globally up to 7 billion facemasks which amount to 21,000 tons of synthetic polymer, were estimated to be used daily during the COVID-19 pandemic, increasing plastic demand and waste. It is yet unknown if respirable MNP debris on the surface of facemasks poses adverse health effects. • Medical plastics include a wide range of products from bags to pharmaceutical containers that leach and expose patients and healthcare workers to MNPs. Further research is needed to assess toxicology and medical significance of MNPs from medical plastics. (2015–2019) == Potential health risks ==

s. 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: On the cellular level • Inflammation • Oxidative stress • Reproductive toxicity, • Neurotoxicity • Disrupted hormone function, potentially contributing to weight gain == Epidemiological studies ==

Despite growing concern and evidence, most epidemiologic studies have focused on characterizing exposures. Epidemiological studies directly linking MPs to adverse health effects in humans still remain relatively limited and research is ongoing to determine the full extent of potential harm caused by MPs and their long-term impact on human health. == Research limitations and scientific uncertainty ==

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. == Prevalence ==

MPs have been found in bloodstreams, and other locations of the body. == Mitigating inhalation exposure to MNPs ==

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. == See also ==