Are We Breathing In Microplastics?-A Soft Touch Perspective
By
Sayan Basak
B.Tech, Department of Polymer Science and Technology,
University of Calcutta
Are airborne fibrous Microplastics (MPs) breathable?
The likelihood that airborne fibrous MPs enter our respiratory system will be dependent upon size. First, it is important to discriminate between the terms inhalable and respirable. Particles and fibers able to enter the nose and mouth and deposit in the upper airway are inhalable, whilst those able to reach and deposit in the deep lung are respirable. Deposition in the airway is a function of aerodynamic diameter and within the respiratory zone; deposition falls off above 5 mm diameter [1]. The World Health Organisation defines fiber as any particle that has a length >5 mm, with a diameter 3:1 [2]. Fibrous MPs that exceed these criteria may be inhaled, but are likely to be subjected to mucociliary clearance in the upper airways, leading to gastro-intestinal exposure.
Some fibrous MPs may, however, avoid the mucociliary clearance mechanisms of the lung, especially in individuals with compromised clearance mechanisms.
Do fibrous microplastics accumulate in the human body?
The biopersistence of inhaled fibrous MPs is related to durability in and clearance from the lung [3]. In vitro tests have found plastic fibers to be extremely durable in physiological fluid: polypropylene, polyethylene and polycarbonate fibers showed almost no dissolution or changes to surface area and characteristics in a synthetic extracellular lung fluid after 180 days. This suggests plastic fibers are durable and likely to persist in the lung [4]. Biopersistence is also connected to length, with longer fibers more likely to avoid clearance [3]. Plastic fibers have been observed in pulmonary tissue [5], suggesting that the human airway is of sufficient size for plastic fibers to penetrate the deep lung. Histopathological analysis of lung biopsies from workers in the textile (polyamide, polyester, polyolefin, and acrylic) industry showed foreign-body-containing granulomatous lesions, postulated to be acrylic, polyester, and/or nylon dust [6]. These observations confirm that some fibers avoid clearance mechanisms and persist. Occupational health risks Studies among nylon flock (fiber) workers suggest there is no evidence of increased cancer risk, although workers had a higher prevalence of respiratory irritation [3]. Interstitial lung disease is a work-related condition that induces coughing, dyspnoea (breathlessness), and reduced lung capacity in workers processing either paraaramid, polyester, and/or nylon fibers [7–9]. Workers also present clinical symptoms similar to allergic alveolitis [6].
These health outcomes are indicative of the potential for MPs to trigger localized biological responses, given their uptake and persistence. Whilst these effects are distinct from those seen after asbestos exposure, the legacy of asbestos toxicology can in-part help predict health effects of fibrous MPs. In silicate-based fibers, length and biopersistence in the airway/lung are the characteristics that govern toxicity and the mechanisms of that toxicity. Whether the same is true for fibrous MPs remains to be determined.
What are the potential mechanisms of toxicity?
Particle effects: inflammation and secondary genotoxicity beyond a certain exposure level/dose, all fibers seem to produce inflammation following chronic inhalation [3]. The general paradigm for fibrous particle toxicity, based on asbestos and manmade vitreous fibers is that upon cell contact, intracellular messengers and cytotoxic factors are released leading to lung inflammation. This potentially leads to secondary genotoxicity following the excessive and continuous formation of reactive oxygen species (ROS). Fibrosis, and in some cases cancer, can manifest after prolonged inflammation [3]. Toxicity is greater for longer fibers [3] as they cannot be adequately phagocytosed, stimulating cells to release an inflammatory mediator [10] that contributes to fibrosis. Poorly-soluble low-toxicity particles have been found to cause lung tumours and inflammation in rats [11], however, information on whether this translates to humans is lacking. Plastic is typically considered inert, yet its biopersistence and the shape of fibrous MPs could lead to inflammation.
There is an urgent need for data on the human health impacts of fibrous MPs. However, before this is determined, it is important to better assess whether and if so, how we are exposed. To this end, a collaboration between environmental, epidemiological and air quality communities is required to set up relevant research programs, which include specific monitoring strategies. Both length and diameter should be included when reporting on the presence of MPs since the diameter is crucial to respirability, whilst length plays an important role in persistence and toxicity. The full spectrum of fibers (both natural and petrochemical-based structures) must also be considered. Within the studies conducted to date, the limit of observation was 50 mm but detection at a smaller scale (<10µm) is crucial.
References-
1. Plastics Europe: Plastics — the Facts 2016, an analysis of European latest plastics production, demand and waste data. Plast Eur Assoc Plast Manuf Bruss P40 2016. [no volume].
2. ICAC: World textile demand. 2017. May 2017.
3. Warheit DB, Hart GA, Hesterberg TW, Collins JJ, Dyer WM, Swaen GMH, Castranova V, Soiefer AI, Kennedy GL: Potential pulmonary effects of man-made organic fiber (MMOF) dusts. Crit Rev Toxicol 2001, 31:697–736.
4. Cesa FS, Turra A, Baruque-Ramos J: Synthetic fibers as microplastics in the marine environment: a review from textile perspective with a focus on domestic washings. Sci Total Environ 2017, 598:1116–1129
5. 5. Napper IE, Thompson RC: Release of synthetic microplastic plastic fibres from domestic washing machines: effects of fabric type and washing conditions. Mar Pollut Bull 2016, 112: 39–45.
6. Dris R, Gasperi J, Saad M, Mirande C, Tassin B: Synthetic fibers in atmospheric fallout: a source of microplastics in the environment? Mar Pollut Bull 2016, 104:290–293.
7. Dris R, Gasperi J, Mirande C, Mandin C, Guerrouache M, Langlois V, Tassin B: A first overview of textile fibers, including microplastics, in indoor and outdoor environments. Environ Pollut 2017, 221:453–458
8. Schneider T, Burdett G, Martinon L, Brochard P, Guillemin M, Teichert U, Draeger U: Ubiquitous fiber exposure in selected sampling sites in Europe. Scand J Work Environ Health 1996, 22:274–284.
9. Free CM, Jensen OP, Mason SA, Eriksen M, Williamson NJ, Boldgiv B: High-levels of microplastic pollution in a large, remote, mountain lake. Mar Pollut Bull 2014, 85:156–163.
10. Waller CL, Griffiths HJ, Waluda CM, Thorpe SE, Loaiza I, Moreno B, Pacherres CO, Hughes KA: Microplastics in the Antarctic marine system: an emerging area of research. Sci Total Environ 2017, 598:220–227.
11. Donaldson K, Tran CL: Inflammation caused by particles and fibers. Inhal Toxicol 2002, 14:5–27.