MICROPLASTICS – A MEGA PROBLEM?
To fret or not to fret
While simultaneously eyeing Ataulfo mangoes at the local grocer, I offered a plastic bag supplied by the store to a fellow shopper. When she politely declined, I wondered if this was because of her concern regarding plastics. Much has been written about this. It surrounds us and is part of our modern everyday life. Countries such as Japan use an abundant amount of plastic to wrap their food yet the Japanese are among the longest living humans. Still, is it harmful?
The first plastic was invented in 1908 by Leo Baekelund, a Belgian chemist who emigrated to the United States, while searching for a substitute for shellac.1 The new material was inexpensive, versatile, light, did not conduct electricity, flexible, and non-flammable. Manufacturers were soon using it to produce everything from radios to appliances. Newer forms appeared with names that are now commonplace, e.g. nylon, polyester, Styrofoam, and polypropylene.
With single use plastics in the 1950s, plastic production exploded becoming critical for medicine, apparel, construction, and food packaging. A decade later in the 1960s, experts began warning about the dangers of plastic pollution especially in the oceans with small particles called microplastics (size 1 micron to 5mm) appearing in marine plankton.1
In addition, these tiny particles, and even smaller pieces called nanoparticles (size < 1 micron), could be swept away by the wind to contaminate not only the oceans but also the soil. Being non-degradable, uptake into plants, then animals, microplastics have now been found in up to 1300 animal species as well as man.1 Human exposure to microplastic particles has been estimated to vary between 74,000 and 121,000 particles per year.2
Microplastics can enter the body by inhalation, ingestion, and skin exposure.3 Once entered, they can be carried by blood to every organ. Not surprisingly, plastic particles have been found in the brain, heart, stomach, lymph nodes, placenta, prostate, and testicles. Microplastics have also been identified in urine, breastmilk, and meconium (baby’s first bowel movement).1 Whether its presence is responsible for causing chronic illness remains unknown and is the subject of intense research.
In 2019 the WHO summarized the evidence about the impact on health following exposure to and removal of microplastics during wastewater and drinking-water treatment.4
In a review of 50 articles on microplastics in drinking water and freshwater, investigators found an enormous range (10 orders of magnitude) of microplastics concentration across individual samples; the most was from wastewater and the least was from river, canal or ground water.5 Treated wastewater reduced microplastic concentration by 3 orders of magnitude. Bottled water had microplastics concentration less than wastewater but higher than tap, river, or ground water. Different shapes including fibres, foam, pellets, fragments, and film were reported. Of the 22 different polymer types measured, the most was polyvinyl chloride and polyethylene, likely reflecting global plastic demand.5
Size does matter. Microplastic particles < 150 microns are assumed to be ingested through the gut to circulate throughout the body but only smaller particles with sizes < 10 microns can enter cells.3 Based on this size requirement, most microplastics found in water, food or beverages are unlikely to be absorbed, and thus studies should focus on particles with sizes < 10 microns.6
To investigate the effects of plastic particles in vitro (applied to human intestinal epithelial cells) and in vivo (rodents fed microplastic particles of sizes 1, 4, and 10 microns), researchers found that only a minor fraction of particles were taken up. In addition, the particles did not interfere with activation of the human macrophage and thus, there was an absence of inflammatory response. Based on these benign findings, the authors concluded that microplastics did not pose a risk to mammalian health.7
Other authors, however, have reported that microplastics may cause physical toxicity including immune reactions, inflammation,8 and cancer.9
A recent report on 10 prostate cancer cases showed the presence of microplastics in 90% of cancerous and 70% of adjacent benign tissue specimens suggesting a possible link with prostate cancer development.10
In an observational study on asymptomatic patients undergoing carotid plaque removal, researchers identified microplastics in 58% of plaques. Patients who had microplastics in their removed plaques had a 4.5X greater risk of late heart attack, stroke or death by 34 months compared with patients who had no microplastics in their plaques.11
These findings, however, are not conclusive of microplastics causing disease. As the particles are extremely small and ubiquitous in air, water, and from any plastic surface, contamination of samples is always possible.12 Unlike media pictures of microplastics appearing as multiple-coloured beads in a glass, identifying them is difficult - visually only with electron microscopy and chemically by mass spectrometry,11 infrared spectroscopy, or Raman analysis.13
Despite the concern of microplastics now becoming recognized in the human body, other man-made materials such as silicone and polyester have been used in humans for decades. Since the 1950s large pieces of polymers as sheets or tubes have been implanted in humans. Polyester Dacron or polytetrafluoroethylene (PTFE - Teflon) has been used for arterial grafts, vocal cord defects, orthopedic joint implants, facial plastic surgery, and hernia repairs.14 To replace arteries, these synthetic tubes can be very long, e.g. some the length from the shoulder to lower thigh. Sheets of PTFE have also been used for hernia repair. Once implanted, a “healing” process occurs whereby the external surface is covered with scar tissue and the internal surface where it contacts with blood, develops a pseudo lining. Considering the chronicity of these materials being used, no research has been conducted to examine if these polyester implants “shed” smaller particles, although there have been concerns with ingested PTFE microplastics from coated utensils and frypans.15
What can one do to reduce the amount of microplastics? Intuitively, it makes sense to use less plastic during food or water storage and to choose natural rather than synthetic clothing materials. But, to actively remove microplastics from water requires either filtration or elimination.
Larger microplastics can be removed with filters. Commercially available filters with pore sizes of 0.2 microns are essential for sterile applications. However, to filter out larger particulates, pore sizes of 0.45 microns may be adequate.16
A surprisingly simple way of removing microplastics from drinking water is the old age method of boiling water.17Researchers showed that boiling hard water (containing more CaCO3) reduced up to 90% of microplastics; in soft water with less CaCO3, around 25% of the microplastics could be removed.18
Although boiling filtered tap water seems to be the most practical solution of decreasing microplastics from drinking water, are humans, nonetheless, just a collection system for micro and nanoparticles?
The answer is unknown. While further research is needed to determine whether microplastics definitively cause illness or are benign hitchhikers on macrophages (like barnacles on a boat) or research contaminants, a poorly understood method of absorption, called persorption, may shed light on how particulates are ingested and excreted.19,20
Microparticles < 10 microns, which includes pollen, spores, starch granules, crystals, and soot particles, once ingested, can be readily identified in the blood within minutes. How they enter the blood is postulated to be a paracellular mechanism involving temporary leaks between the intestinal cells that allow these particles to travel into the bloodstream. From there, the particles can travel throughout the body and be eliminated by numerous ways including urine, fecal, bile, lactation, transplacental transfer, and exhalation.20 As these locations (urine, breast milk, meconium) are also where microplastics have been identified, this suggests that persorption can expel microplastics!
The field of discovery into microplastics is just beginning. Controversy exists as to the best method of identifying microplastics (see above), determining whether their appearance in diseased tissue is due to causation or a bystander effect, and whether its metabolism is possibly through persorption as a method that can be leveraged to increase their elimination.
The US government recently recognized the importance of microplastics as a potential threat to health and announced funding of US$144M for the STOMP (Systematic Targeting of MicroPlastics) program, as an advanced research project to measure, research, and remove microplastics and nanoplastics in the human body.21
As this program is being rolled out, it is instructional to review a recent study by Korean researchers on 36 healthy volunteers aged 30-55. In 32 patients who had evidence of microplastics in their blood, an association between microplastic counts and coagulation parameters was identified. However, no patients experienced any clotting disorder. Of interest, more microplastics were detected in people with higher education (possibly due to a preference for bottled rather than tap water) and the percentage of plastic containers amongst all the containers in the refrigerator.13
Of even more interest (at least to me) was that 4/36 volunteers (11%) had no evidence of microplastics in their blood. The authors did not describe those volunteers any further but that’s a rich area to study, i.e. why do some people have no evidence of microplastics in their blood even though it is ubiquitous? What does their lifestyle involve? Are they able to eliminate microplastics more efficiently through mechanisms such as persorption?
So, readers, does the fear of microplastics impact how you live your life?
REFERENCES
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4. Microplastics in drinking water. WHO. Aug. 28, 2019 https://www.who.int/publications/i/item/9789241516198
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13. Lee, DW., Jung, J., Park, Sa. et al. Microplastic particles in human blood and their association with coagulation markers. Sci Rep 14, 30419 (2024). https://doi.org/10.1038/s41598-024-81931-9
14. Ngan V. Polytetrafluoroethylene implant. Derm Net 2022. https://dermnetnz.org/topics/polytetrafluoroethylene-implant
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16. Morland C. Understanding filter pore sizes: Finding the right filter. https://internationalfilterproducts.com/en-ca/blogs/ifp-blog/understanding-filter-pore-sizes-finding-the-right-filter
17. Nield D. There’s a surprisingly simple way to remove microplastics from your drinking water. Science Alert Health. March 5, 2024. https://www.sciencealert.com/theres-a-surprisingly-simple-way-to-remove-microplastics-from-your-drinking-water
18. Zimin Yu, Jia-Jia Wang, Liang-Ying Liu, Zhanjun Li, and Eddy Y. Zeng. Drinking Boiled Tap Water Reduces Human Intake of Nanoplastics and Microplastics. Environmental Science & Technology Letters 2024 11 (3), 273-279. DOI:10.1021/acs.estlett.4c00081
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