Summary
A new study from Spain’s Autonomous University of Barcelona reveals that tea bags made from nylon, polypropylene, and cellulose release billions of micro- and nanoplastic particles when steeped in boiling water.
These particles, which can enter human intestinal cells, may pose health risks, potentially affecting the digestive, respiratory, endocrine, and immune systems.
Researchers urge regulatory action to mitigate plastic contamination in food packaging.
Consumers are advised to use loose-leaf tea with stainless steel infusers or biodegradable tea bags to minimize exposure.
I’m not totally sure what you mean by “get out more or less of the dissolved particles”, but I think I understand where your confusion lies. You keep referring to quantities, i.e. mass or particle counts. Their data is reporting these things as concentrations.
It should be obvious to you that 7.14g of salt dissolved in 2ml of water will produce a highly concentrated solution (saturated, in fact), whereas the same 7.14g dissolved in 350ml of water will produce a dilute solution. The concentration of the first one is 3.57g/ml, but the concentration of the second is 0.0204g/ml.
If somebody then turns around and says that 7.14g of salt dissolved in a mug of water will produce a concentration of 3.57g/ml, it should be readily apparent that they are incorrect. That is in effect what the authors are saying by reporting their results as particles/ml and then saying that those numbers are representative of what you might expect when brewing tea under normal conditions.
Does that all make sense?
Hmm, interesting. Maybe I’m being dense here. Let’s say that the teabag is that 7.14g of salt you mentioned - a chunk of salt, let’s say. They either A) try to dissolve 300 of those (each 7.14g) in 600 ml of water or B) they dissolve 1 chunk in 350 ml water. Like you said, they either report A) 3.57 g/ml or B) 0.204 g/ml.
I’m really just saying that either way, it’s still 7.14 g/chunk. Quite a lot of salt/particles per chunk/teabag.
I think maybe I don’t have an issue with them reporting the concentration because I didn’t interpret them as saying that they were saying there’s a billion particles per ml of a regular cup of brewed tea - it was always apparent to me that it was about the number of particles in a teabag (in this case, half a teabag with just a ml volume). I think we’re ultimately just arguing clarity of their language.
In a sense, but clarity of language can be the difference between accurate conclusions and misrepresentation. Just on data presentation alone, formal issuance of a correction is absolutely necessary.
Following on from that is where the issues with study design and methodology come in, and in my opinion they are both so flawed as to lead to spurious conclusions.
The other major problems I see so far:
as mentioned previously, their brewing methodology is so different from what would be done under normal conditions/at home that comparison between the two is meaningless. A good paper should discuss these differences and explain why some conclusions can still be drawn, but this one just makes a direct comparison.
the authors used empty mesh sleeves from an unnamed aliexpress vendor for their samples. We have no idea whether these sleeves are in use by any tea manufacturer, we don’t know anything about how they were made, and we don’t even know whether they were intended for food usage.
one of the three samples produced only cellulose particles, which a) isn’t a plastic and b) is a component of plant cell walls. I don’t know the cellulose particle concentration in a kale smoothie, but I’m certain that it’s higher. And yet the authors still just report this figure alongside the others.
Ultimately, the only thing this paper demonstrates is that certain types of thin-fibre plastic will, when handled roughly, shed nanoparticles. This isn’t a new conclusion, and doesn’t provide us with anything actionable with respect to our tea drinking habits.
I’ve mentioned it before in another comment, but this conclusion about plastic microparticles is a very minor part of their paper - it has already been established by Hernandez et al in 2019 (Environ Sci Technol) that billions of particles were released from plastic teabags, and another study by Banaei et al from the same lab as the OP posted study in 2023 (J Haz Mat) adapted/refined the method to try to mimic traditional tea preparation. That method section may give you a bit more insight as to what exactly they did and why, e.g. they say “The stirring speed was gradually augmented since the weight of the teabags slowed down the stirring speed…” And “the teabags were squeezed… eliminated… [And] the remaining solution was left to cool down on constant stirring…” I’d advise you to look at that paper - it might actually address your problem #1.
For #2, that’s fair. I think they had the details on the chemical composition of those (nylon-6), but they didn’t do any digging on if any manufacturers use them. I’m not exactly sure that’s in the scope of their study as they were just looking for any consumer teabags that could reasonably be used and consumed by people.
For #3, that’s also fair, and if you look at their data in the microscopy sections, it doesn’t look like cellulose gets taken up by the different cell lines. I think you can think of it as a control for plastic microparticles, but yeah, I guess they didn’t specify. That’s on them.
I think the novelty of this study isn’t the plastic particles per se but it is that they looked at the biological interaction between these particles and intestinal cells. There’s a lot there to discuss there in terms of the science and whether they could draw the conclusions they do. They did not show mechanism of action, such as what sorts of biology get affected after uptake of these particles (e.g. they could have done some transcription studies or looked at inflammatory markers or other transcription factors that get up/downregulated, or looked at what cytokines get secreted by ELISA or luminex), which all points to a severe limitation of the study. The uptake experiments also simply don’t have the right controls - they should have used other particles to see whether it’s simply a difference in cell uptake that’s independent of plastic. They could’ve also determined which organelle the particles were sequestered into rather than just saying it colocalized to the nucleus. And much more.
Long story short, from my perspective as a scientist, the issues you bring up are mostly trivial because it seems like there’s no standard protocol in place, and what they did was reasonable (also reproducible via stir bar and temp) even though it is not exactly how you’d brew tea at home. The study has its limitations, and much of it is on the biological side. I don’t have the expertise to comment much on their chemical analytical techniques.
You should know that critical methodological issues were reported with Hernandez, viz. they failed to discriminate particle identity. A recreation of their experiment demonstrated that the vast majority/virtually all of the particles were actually soluble oligomers that were subsequently crystallized by their preparation technique, i.e. not microplastics.
Your reading of their paper is extremely generous, but I’m not sure where you get the idea that analysis of the interaction between microplastics and endothelial cells is novel; the citations in this paper alone should be enough to tell you otherwise. The sole novelty of this paper is in drawing a link between existing studies on cell interaction and real-world situations, which is evident right from the title: “Teabag-derived micro/nanoplastics as a surrogate for real-life exposure scenarios”.
There may well be further room for experimentation in this arena, but this paper falls flat. Their methodology is so far off anything that could be described as “real-world” that it is spurious to draw any subsequent conclusions.