Microplastics are polluting the oceans and also the air.
Microplastics introduction and definitions
Microplastics are becoming a topic of growing concern due to the possible adverse effects related to their presence in the environment. Microplastics derives mainly from wrong plastic waste disposal or wrong recycling of plastic. If release in environment, plastic objects are subject to phenomena of fragmentation and abrasion; these mechanisms will degrade plastic waste in fragments smaller and smaller.
Furthermore, microplastics could be already present in microscopic dimensions in some products (for example, microbeads in personal care products). Plastic materials are highly resistant to biodegradation and they can persist in the environment for hundreds of years.
Microplastics due to the small dimensions and lightweight could be easily transported by water and wind, in fact they are found in each environmental matrix and they are spread in the whole Earth. Adverse effects could be affected biological organisms and humans too; microplastics can be ingested or inhaled and thus entered in food chain, furthermore, can adsorb toxic substances or bacteria on the surface.
Microplastics are defined as plastic particles with dimension in a range between 100 nm and 5 mm. Recently, they are distinguished in microplastics (1 micrometer – 5 mm) and nano plastics (every plastic particle with dimension less than 1 micrometer).
To have an idea of dimensions, the diameter of human hair is around 50-70 micrometer and the smallest particle that can be observed with naked eye is around 40 micrometers. Based on their origin, they can be divided into primary and secondary microplastics.
Primary microplastics arise from textile (microfiber) or are contained in products like cosmetics, they are defined “primary” because they are already in a microscopic dimension.
Secondary microplastics arise from abrasion and/or fragmentation of bigger plastic objects.
The ubiquity in environment and the potential adverse effects oh human health, on microorganism and on ecosystem make microplastics a topic of big concern.
However, this topic is complex due to polymer shape and characteristics, in fact microplastics are find in different shapes, like fibers, granules, spheres, films, and pellets (Huang et al., 2020), and in different chemical compositions due to different polymers or mixture.
The most utilizing polymers are PP, PE, PET, PVC, PS and PA. The main critical points are related to the number of studies that are still limited, especially for atmosphere and air matrix, and the lack of legislation, regulation and a standard method for sampling and analysis.
In the next figure (Huang et al., 2020) are show the photo of some microplastics found in the air (a, b, and c are fibers; d,e, are fragments; f is a granule).
Sampling and Analysis of Airborne Microplastics
Despite a lack of standard regulation, sampling procedure and analysis of microplastics in the environment generally follows some steps as: sampling, preparation and separation, identification, and analysis (Chen et al., 2020; Zhang et al., 2020). More detailed scheme is shown in the next figure (Enyoh et al., 2019).
Sampling of Airborne Microplastics and Sample Preparation
To date airborne microplastics are less studied but it is necessary the characterization of all aspects that regards microplastics also in this environmental matrix. Particles dispersed in the air can be transported for a long distance and based on the dimensions, can be inhaled through respiration and, in case of nano plastics, can be bioaccumulated.
To date there are two methods for sampling airborne microplastics, active (through pump) and passive (that use particle deposition by gravity). Sampling can be done indoor or outdoor; it is possible to collect air through sampler equipped with filter (that collect airborne particles) or dust deposited by gravity through aspiring instruments or brushes.
Sampling made by active method allows to sample airborne particles, while the passive one allows to sample the particles deposited by gravity or after the wet deposition of airborne particles by rain or snow, and thus collect the particles that are trapped or that acts as condensation nucleus.
Also, for sampling of atmosphere microplastics it is necessary to treat the sample collected before the analysis. It is necessary to remove everything is not of interest, sample pre-treatment is necessary to make it the most representative as possible and to avoid underestimation or interference during the analysis.
First, it is necessary to remove organic substance, this process is done using oxidants, acids or bases, for example H2O2, HNO3, HCl, KOH, NaOH. Also, for these processes there is not a standard reference method so in the specific literature there are some methodologic differences between different studies.
It is utilizing mainly H2O2 at 30%, ZnCl2 1,6 g/cm3, NaClO at 6-14%. It is possible to also use Fenton reagents (mix of H2O2 and Fe2+ ions) that are more efficient in digestion of organic material. In this phase is necessary to use substances not aggressive to avoid degradation of particles.
Later, microplastics can be separated by gravity in a solution, based on their density some can float or deposit. Polyethylene, for example, has a density in a range of 0,92-0,97 g/cm3, so a little bit lower than water, while polymers like PVC and PET have density in a range of 1,15-1,70 g/cm3 and 1,30-1,60 g/cm3, respectively.
In the specific literature, are used solutions of zinc chloride 1,6-1,7 g/cm3, sodium chloride 1,2 g/cm3, and sodium iodide 1,8 g/cm3. After separation, microplastics must be dried and stored up to the analysis.
Regarding the impact on human health, airborne microplastics (like all airborne microscopic particles) can be introduced in the organism through respiration. Vianello et al. (2019), sampled indoor air using a breathing thermal manikin that simulate human breathing.
Microplastics are sampled on filter with pore diameter of 0,8 micrometer. Maximum exposure found was 16,2 NMP/m3 (number of microplastics per cubic meter), that corresponds at an inhalation ratio of 11,3 MP/h; this means that through inhalation, a man with a light activity could potentially inhale up to 272 MP in 24 hours.
The importance of this topic collides with the necessity to have a standard method for sampling and analysis of microplastics, to have results more reliable and more comparable. Developing a method could give the possibility to have more studies and consequently more knowledge on this topic, that are still extremely low especially for the atmosphere and the air matrix.
The interest of TCR Tecora is oriented to start a theoretical and practical path specifically with the aim to improve one of the more critical point but at the same time one of the more important, the sampling method.
TCR Tecora is looking for a partner to enhance this topic and is designing a solution to improve the sapling technique.
Chen, G., Fu, Z., Yang, H., & Wang, J. (2020). An overview of analytical methods for detecting microplastics in the atmosphere. TrAC – Trends in Analytical Chemistry, 130, 115981. https://doi.org/10.1016/j.trac.2020.115981
Enyoh, C. E., Verla, A. W., Verla, E. N., Ibe, F. C., & Amaobi, C. E. (2019). Airborne microplastics: a review study on method for analysis, occurrence, movement and risks. Environmental Monitoring and Assessment, 191(11). https://doi.org/10.1007/s10661-019-7842-0
Huang, Y., Qing, X., Wang, W., Han, G., & Wang, J. (2020). Mini-review on current studies of airborne microplastics: Analytical methods, occurrence, sources, fate and potential risk to human beings. TrAC – Trends in Analytical Chemistry, 125, 115821. https://doi.org/10.1016/j.trac.2020.115821
Vianello, A., Jensen, R. L., Liu, L., & Vollertsen, J. (2019). Simulating human exposure to indoor airborne microplastics using a Breathing Thermal Manikin. Scientific Reports, 9(1), 1–11. https://doi.org/10.1038/s41598-019-45054-w
Zhang, Y., Kang, S., Allen, S., Allen, D., Gao, T., & Sillanpää, M. (2020). Atmospheric microplastics: A review on current status and perspectives. Earth-Science Reviews, 203(December 2019), 103118. https://doi.org/10.1016/j.earscirev.2020.103118
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