What Are Microplastics?

What microplastics are, where they come from, and how they enter our bodies

Microplastics are tiny fragments of plastic smaller than 5 millimeters -- some so small they're invisible to the naked eye. They come from the breakdown of larger plastic products, synthetic clothing fibers, food packaging, and industrial processes. Research has now confirmed that microplastics are present in human blood [1], drinking water [2], and the food we eat [3], meaning virtually everyone alive today carries some amount of plastic in their body.

Microplastics are formally classified as plastic particles less than 5mm in diameter, while nanoplastics are smaller still -- under 1 micrometer (0.001mm). They fall into two broad categories. Primary microplastics are manufactured small, such as the microbeads once common in cosmetics and exfoliating scrubs, or the plastic pellets (nurdles) used as raw material in manufacturing. Secondary microplastics result from the degradation of larger items: UV radiation, mechanical wear, and weathering break down bottles, bags, tires, and textiles into progressively smaller fragments [4].

The routes into the human body are well-documented. Ingestion is the dominant pathway. Bottled water has been found to contain significantly more microplastic particles than tap water, with some brands showing concentrations of over 10,000 particles per liter [5]. Food sources include seafood (which ingests ocean microplastics), salt, honey, beer, and produce grown in soil amended with plastic-contaminated compost [3]. Inhalation is another significant route -- indoor air often contains higher concentrations of airborne microplastic fibers than outdoor air, shed primarily from synthetic textiles, carpets, and upholstery [4]. Dermal exposure through cosmetics and personal care products is a third, though likely less significant, pathway [3].

The WHO estimates that humans may ingest on the order of tens of thousands to hundreds of thousands of microplastic particles per year, depending on diet and lifestyle factors [3].

The landmark 2022 study by Leslie et al. provided the first direct evidence of microplastics circulating in human blood. Using pyrolysis-gas chromatography/mass spectrometry, researchers analyzed blood samples from 22 healthy volunteers and detected quantifiable concentrations of plastic particles in 17 of them (77%). The most common polymers found were PET (polyethylene terephthalate, used in drink bottles and food packaging), polystyrene (used in disposable food containers), and polyethylene (the most common plastic worldwide, used in bags and packaging). The mean total concentration of microplastics in blood was 1.6 micrograms per milliliter [1].

The drinking water pathway has been thoroughly characterized. Koelmans et al. conducted a systematic review of studies on microplastics in drinking water and found that while concentrations vary widely by geography and source, microplastics are consistently detected in both treated and untreated water. Conventional water treatment processes (coagulation, filtration, disinfection) remove a substantial fraction but not all particles, particularly at the nanoscale [2]. Mason et al. tested 259 individual bottles of water from 11 brands across 9 countries and found an average of 325 microplastic particles per liter, with some samples exceeding 10,000 particles per liter. Notably, bottled water contained roughly double the concentration of microplastics compared to tap water, likely due to contamination from the plastic packaging itself [5].

The WHO's 2022 technical report synthesized the available evidence on dietary and inhalation exposure. It concluded that while microplastics are ubiquitous in the food chain and ambient air, significant data gaps remain regarding nanoplastic exposure, long-term bioaccumulation kinetics, and the relative contribution of different exposure routes. The report called for standardized analytical methods and large-scale epidemiological studies to better quantify risk [3].

Campanale et al. reviewed the full spectrum of human exposure sources and estimated that the average person ingests approximately 0.1 to 5 grams of microplastic per week, depending heavily on dietary habits (seafood consumption, bottled vs. tap water, processed vs. whole foods) and environmental context (urban vs. rural, indoor air quality). They noted that exposure assessments remain uncertain due to the lack of standardized measurement protocols across studies [4].

References

Microplastics in human bloodLeslie HA, van Velzen MJM, Brandsma SH, Kroesbergen J, Lamoree MH. Environment International, 2022. PubMed 35395168 →
Microplastics in Drinking Water: A Review and AssessmentKoelmans AA, Mohamed Nor NH, Hermsen E, Kooi M, Mintenig SM, De France J. Environmental Science & Technology, 2019. PubMed 33130380 →
Dietary and inhalation exposure to nano- and microplastic particles and potential implications for human healthWorld Health Organization. WHO Technical Report, 2022. Source →
Quantifying Human Exposure to Microplastics: An Emerging Environmental Health ConcernCampanale C, Massarelli C, Savino I, Locaputo V, Uricchio VF. Environmental Science & Technology, 2020. PubMed 36805682 →
Synthetic Polymer Contamination in Bottled WaterMason SA, Welch VG, Neratko J. Frontiers in Chemistry, 2018. PubMed 29963051 →

What Are Microplastics?

References

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