Briefing Note in response to Ma, J., Ladd, D. M., Kaval, N., & Wang, H. S. (2025). Toxicity of long term exposure to low dose polystyrene microplastics and nanoplastics in human iPSC-derived cardiomyocytes. Food and Chemical Toxicology, 115489.
Main takeaway: This study should not be a cause for concern regarding microplastics and heart health. While the paper is generally clear in reporting what the researchers did, I think they overinterpret the results.
Response from Oliver Jones, Professor of Chemistry, RMIT University, Melbourne, Australia There are several methodological considerations to note with this paper. The first is that the work is on cardiomyocytes (heart muscle cells) in a petri dish exposed to polystyrene microplastics. In fact, the heart cells were stem cells that had been developed into heart cells, so they were not quite true cardiomyocytes. This might be a case of “Potāto, Potáto”, but regardless, the heart is a complex organ formed of several different types of cells and tissues. While cell monocultures (one type of cell) are useful for screening for things you might want to look at in more depth, they are simple models that don’t reflect real life. The most you can say from this paper is that if you grow heart cells in a dish and put polystyrene on them, you might see a small metabolic effect. We can’t say the same happens in a real heart because cells in a petri dish are not a real heart.
To their credit, the authors try to use environmentally relevant concentrations for their work. However, only one type of plastic, polystyrene microbeads, was used for this work. Microbeads have been phased out of most, if not all, products, and polystyrene far from the most common plastic found in the environment. However, it is readily available and is often used in such studies, even if it is not the best plastic to use 1.
There is a question of whether in vitro methods are useful for assessing the impact of microplastics on health at all 2. On one hand, in vitro assays are useful because they are relatively quick and easy to do, don’t cost a lot, and don’t raise any ethical concerns. On the other hand, they don’t mimic what a body is really like, as the conditions in a petri dish are not those of the body. For example, plastics vary greatly in their density. If the density of the plastic is lower than that of the cell culture medium (usually around 1 g cm−3), it will float at the surface of the medium and will not be able to establish contact with the cells, which are typically located at the bottom of the culture dish. Conversely, if they are denser than the media, they will sink and be in direct contact. Both options introduce error, but in general, conventional in vitro assays are not suitable for evaluating the toxicity of buoyant samples such as polystyrene.
An additional issue is that the dispersant in which the particles are supplied can have an effect on cells 3. This might be misinterpreted as an effect introduced by the particles when it isn’t.
It is also unclear how microplastics would reach the heart. The primary way microplastics enter the body is through breathing them in or ingesting them in our food. Dermal (skin) absorption has been mentioned once or twice in the literature, but it is not clear if this actually happens. While a small amount of ingested microplastic might possibly circulate in the blood, there is at best inconsistent evidence for this 4.
Despite the fact that the study only looks at cells in a petri dish the authors claim the work “…is relevant for understanding of MNPs toxicity in human heart” which I think is incorrect. They also state that microplastics are “…increasingly recognised as a threat to human health”. The World Health Organisation (WHO) actually says there is no clear evidence that microplastics pose a threat to human health 5. Now, this is not the same as saying they are safe; it simply means there is no proof they pose a risk, despite the numerous papers published on microplastics each year.
So in short, I don’t think this paper shows your heart is at risk from microplastics. Poor diet, lack of exercise are likely much more relevant risk factors for heart health for most of us.
References
1. Xu, J.-L.; Lin, X.; Wang, J. J.; Gowen, A. A., A review of potential human health impacts of micro- and nanoplastics exposure. 2022, 851, 158111.
2. Forest, V.; Pourchez, J., Can the impact of micro- and nanoplastics on human health really be assessed using in vitro models? A review of methodological issues. 2023, 178, 108115.
3. Stock, V.; Böhmert, L.; Coban, G.; Tyra, G.; Vollbrecht, M.-L.; Voss, L.; Paul, M. B.; Braeuning, A.; Sieg, H., Microplastics and nanoplastics: Size, surface and dispersant – What causes the effect? 2022, 80, 105314.
4. Kuhlman, R. L., Letter to the editor, discovery and quantification of plastic particle pollution in human blood. 2022, 167, 107400.
5. WHO Dietary and inhalation exposure to nano- and microplastic particles and potential implications for human health; World Health Organization: Geneva, Switzerland, 2022. https://www.who.int/publications/i/item/9789240054608