Over course of the past several years, the issue of microplastics has become a topic of great concern to the general public. These tiny plastic particles, smaller than even a grain of sand, can be found almost everywhere on earth (Parker 2020), and are able to infiltrate into almost every system of the human body (Cox et al. 2019). Many scientists are worried that microplastics are dangerous to human health, as there is a large amount of evidence that these particles are damaging to both mammals (Yong et al. 2020) and aquatic organisms (Haegerbaeumer et al. 2019). Unfortunately, there has been a lack of actual human studies, due to the ethical dilemma of purposefully exposing people to a possible toxin, so there is a knowledge gap in understanding the dangers of microplastics to humans. In response to this lack of research, scientists at Florida State University decided to study the effects of microplastics on human lung cells in an article entitled “Exposure of Human Lung Cells to Polystyrene Microplastics Significantly Retards Cell Proliferation and Triggers Morphological Changes.” The results of this study did in fact find that microplastics could possibly be causing respiratory harm, and the findings may have a significant impact on how seriously the issue of microplastics is taken in the future.
Microplastics are plastic particles that are less than 5 millimeters (mm) across, although most are much smaller. The specific size of the particles used in the study were “nanoplastics,” or microplastics that are less than 1000 nanometers (nm) in diameter (Goodman et al. 2021). Microplastics can either come from the breakdown of larger plastics or can be originally manufactured at that size (Lim et al. 2021). These particles are small enough to be carried almost anywhere by air or water currents, leading to their rapid proliferation all over the earth. The main ways that humans ingest microplastics are either by consuming them through food or water, or by inhaling particles that are small enough to be airborne (Cox et al. 2019). Of these two routes, the latter is of particular concern to scientists, given that studies have shown that particles of less than 10 micrometers (μm) can infiltrate deep into the lungs (Goodman et al. 2021).
In order to study the effects of such types of microplastics, a study was conducted by Kerestin E. Goodman, Joan T. Hare, Zahraa I. Khamis, Timothy Hua, and Qing-Xiang Amy Sang, all of whom are researchers in The Department of Chemistry and Biochemistry at Florida State University. Funding came from grants from Florida State University and from an Endowed Chair Professorship in Cancer Research in the form of anonymous donations to Qing-Xiang Amy Sang, and the researchers declared no conflicts of interest. They conducted the study in 2020 at Florida State University, and it was published in the journal Chemical Research in Toxicology on March 15, 2021. According to the researchers, this study was motivated by several factors, including the increasing general concern about the possible effects of microplastics and studies showing how common lung microplastic contamination has become.
When beginning the study, the researchers hypothesized that exposing lung cells to microplastics would harm cell morphology (structure), metabolic activity, and proliferation (growth and division). To test this, the scientists used samples from a cancerous human lung cell line, due to their fast proliferation rate. These cells were cultured onto a 96 well plate, which is a tray with 96 cylindrical indents, and the cells were then allowed to grow for 12 hours uninterrupted. After 12 hours, polystyrene microplastic particles (PS-MP’s) of 1 μm and 10 μm were added to the cultures at various concentrations. A control culture that had no microplastic exposure was also grown at the same time under the same conditions to provide a standard to compare the altered cells to. The researchers took samples from the cultures every 24 hours for 96 hours. They then analyzed the results, mostly trying to understand how the cells had changed in shape, metabolic activity, and reproduction (Goodman et al. 2021).
Upon analysis, the study yielded several useful insights. First, it was found that exposing the cells to microplastics drastically changed their shape. Instead of staying tightly packed and pillow shaped like normal lung cells, the exposed cells separated from each other and started to grow filopodia, which are growths that help them navigate their environment. These are not normally seen in lung cells. Another effect of the microplastics was that exposed cells had lower metabolic activity than the control cells, with a greater concentration of particles being associated with lower activity. Microplastic exposed cells were far less able to proliferate; the contaminated cells not only grew slower individually, but replicated less frequently, leading to there being only 30% as many exposed cells compared to control cells. One final result was that the 1 μm particles were found to infiltrate into the cells, eventually making their way to the nucleus in a large proportion of exposed cells. These results are important because they provide evidence that microplastics can cause significant damage to lung cells, at least in a laboratory setting.
Unfortunately, this study had several major limitations. The foremost problem was that all results were obtained from an invitro (petri dish) study, meaning they cannot be applied to actual human bodies. Regrettably, this issue is unavoidable due to the unethicality of making human participants inhale microplastics, given the knowledge that they are likely harmful. Another issue is that the cells used in the experiment were from a cancerous culture. The article explains that the rationale behind this was that cancerous cells proliferate very quickly, making them easier to study. While not a huge issue, one should keep in mind that due to the cancerous nature of the studied cells, it is possible that healthy lung cells could respond differently to microplastic exposure. An additional possible limitation of this study is that it only examined the effects of two sizes of microplastic particles, which both had the same spherical shape. The issue with this is that it makes the results of the study less applicable to real life, because actual inhaled microplastics come in a much greater variety of shapes and sizes. However, there is a logic behind this decision, being that the size of the particles that were used are small enough to penetrate deep into the lungs, so are likely the most dangerous variety (Goodman et al. 2021). Additionally, the researchers were not aiming to comprehensively analyze the effects of every type of microplastic, so the validity of the results is not damaged by this limitation.
This study could potentially have very large implications for public health. While not yet proven, if the results of microplastic exposure in the study hold true for real human lungs, then microplastics are likely causing serious lung damage for many people. According to the authors of the study, the separation and morphological changes found in the study are of particular concern, as similar changes caused by other respiratory diseases have been found to cause serious lung damage. Even more concerning is the fact that the plastic builds up inside of the lungs, as the body has no means of breaking down this type of material, meaning that if such damage is occurring, there is not currently any solution (Goodman et al. 2021). A possible next step for researchers is conducting similar studies with even more types of microplastics and tissues, which would both verify these results and provide even more insight on the damage microplastics are causing. Animal studies would also be useful to test if the invitro results hold true for living creatures, as would retrospective studies examining how microplastics effect people who have already been exposed. In terms of society, hopefully this study provides a motivation for reducing the amount of microplastic pollution that is being generated, and encourages more funding to be given to research on this urgent and serious issue.
References
Cox KD, Covernton GA, Davies HL, Dower JF, Juanes F, Dudas SE. 2019. Human consumption of microplastics. Enviro Sci Tech [Internet];53(12):7068-7074. https://pubs-acs-org.libproxy.lib.unc.edu/doi/10.1021/acs.est.9b01517.
Goodman KE, Joan HT, Khamis ZI, Hua T, Sang QXA. 2021. Exposure of human lung cells to polystyrene microplastics significantly retards cell proliferation and triggers morphological changes. Chem Res in Toxic [Internet]. 34(4);1069-1081. https://pubs.acs.org/doi/pdf/10.1021/acs.chemrestox.0c00486.
Haegerbaeumer A, Mueller MT, Fueser H, Traunspurger W. 2019. Impacts of micro- and nano-sized plastic particles on benthic invertebrates. Front Environ Sci [Internet]. 7;17. https://vb3lk7eb4t.search.serialssolutions.com/?sid=google&auinit=A&aulast=Haegerbaeumer&atitle=Impacts+of+micro-and+nano-sized+plastic+particles+on+benthic+invertebrates:+a+literature+review+and+gap+analysis&id=doi:10.3389/fenvs.2019.00017&title=Frontiers+in+environmental+science&volume=7&date=2019&spage=17&issn=2296-665X.
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Parker L. 2020. Microplastics have moved into virtually every crevice on Earth. National Geographic [Internet]. https://www.nationalgeographic.com/science/article/microplastics-in-virtually-every-crevice-on-earth.
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