plastic, microplastics, pollution, placenta,
placentas, birth, women, pregnancy, medicine, biology, respiratory system, gastrointestinal
system, lungs, intestine, bloodstream, immune system, lymphatic
system, epithelium, endocytosis
Part 1 is here
Part 2 is here
Ascolta l'episodio in italiano
Ooooh, hello dear English speaking-reading-hearing listener, welcome back to me, @sciencemug, the blog/podcast/twitter&instagram accounts/entity behind the unsuccessful e-shop stuffngo on zazzle.com which tells you science stories while assessing the financial risks of buying seventy-six hundreds tons of pineapples with the idea to resell them to the Italian pizza industry, aaand which talks to you thanks to the voice, kidnapped via a voodoo-wireless trick, from a veeery very very dumb human.
Aaand which does all of this in English-question-mark, a language that is to proper English what Cosmic Sin sf movie is to something even remotely different from a cosmic waste of money aaand a sin committed by the director, screenwriter, producers, cast and film distributors towards the audience, and the gods of storytelling.
A group of Italian researchers (aka the Italian Brains, aka the ITBs) study human placentas in search of microplastics fragments (MPs), that is plastic particles smaller than half a centimeter. In doing so, the researchers for the first time ever find such pollutants in the placentas of women in good health and who have had normal pregnancies and deliveries.
The Italian research team is lead by Medical Doctor Antonio Ragusa, Head of the Department of Woman, Mother and Newborn of the San Giovanni Calibíta Fatebenefratelli Hospital, in Rome, and the group publishes its study (P) on the science journal Environment International.
Now, people, so far I’ve told you: how the Italian Brains select the pregnant women for their study, how they design and execute a plastic free protocol to collect the placenta samples, what kind of technique they use to analyze them, aand finally what are the characteristics of the microplastics found in said placenta samples.
In this episode, dear listener, I’m gonna tell you the Italian Brains’ idea of how the darn super-tiny pieces of plastics manage to travel from the outside world all the way deep down into the placenta, that is the organ in charge to basically feed and protect the developing fetus.
Well, dear listener, doctor Ragusa and colleagues think that the MPs most probably reach the placenta viabloodstream.
As mentioned in the previous episodes, indeed, the microplastics the Italian Brains find are veeery small, about 5 to 10μm, meaning form one twelfth to one sixth of an average human hair’s diameter, meaning that these things are small enough to surf the bloodstream and travel, like that, through the human body. Proof of it is that 5-10μm particles have already been detected “as foreign bodies in human internal organs” by other researchers (P).
The Italian Brains, though, admit they don’t know how exactly the MPs end up in the bloodstream. Yet, they think the entry ways to the human body can be two: the respiratory system, and the gastrointestinal tract (GIT).
From there, then, the ITBs say, the MPs can reach the bloodstream and eventually the placenta.
And of course you, dear curious listener, want to know exactly how.
Well, pal, let’s break down these two entry mechanisms, ok? Ooook!
Let’s start with the respiratory system pathway.
So, there are the upper and the lower respiratory tracts.
To be clear: the trachea splits into bronchi and, inside the lungs, each bronchus splits into secondary and tertiary bronchi which go on with the branching businesses to form smaller airways named bronchioles. Such bronchioles, in turn, keep branching till they end in veeery tiny air sacs called alveoli which cluster together into alveolar sacs. Aaaand here’s where the actual gas exchange happens, on the very surface of each alveolus thanks to a “network of capillaries carrying blood that has come through veins from other parts of the body” (see).
|Lungs & microplastics (by @sciencemug)|
Ok, now, both respiratory tracts, from the nasal cavity down to the bigger bronchioles, are coated with mucus, that is a sticky, slimy, slippery gel, produced by glands, which is mostly made of water (95%) and mucins (5%), namely proteins that “provide lubrication, protection, resistance, and resilience to toxic challenges at the mucosal surfaces” (see).
Mucus primary function, besides humidifying the airways, is basically to form a barrier against infectious and irritating stuff (like microrganisms, smoke, pollen etc). The bad guys, indeed, get stuck into the mucus, and then moved out your human body.
How, you’re asking, dear listener?
Well, you know pal, both human respiratory tracts, from nose to the bronchioles, are lined by the ciliated epithelium. Epithelium, folks, besides being those cells that “make up the outer surface” (see) of your human body, is a general term that identifies the “layers of cells that line hollow organs and glands” (see).
So, the just mentioned ciliated epithelium is an epithelium of the respiratory tracts that is made of cells equipped with hairlike structures called cilia.
There are 10 cilia per square centimeter in the respiratory tree, and these cilia all beat “synchronously in a characteristic whip-like fashion propelling mucus [and its nasty hosts] from the distal airways to the nasopharynx” (see) from where you humans drip, blow, sneeze, cough, spit etc ‘em out.
So, dear listener, to sum up: your human airways have a kinda glue, the mucus, that entraps the bad stuff you inhale, and this kinda blob loaded with nasty stuff is than carried away by kinda hairy cells, the ciliated epithelium.
Now, with this whole picture in mind, pal, let’s go and see what’s the ITBs’ idea of how microplastics manage to enter the human body via the respiratory system.
But first, a commercial break!
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Oook, dear listener, let’s see how small pieces of plastic manage to take a dive into your human bloodstream by entering your human body through the respiratory system.
The Italian Brains say that in the upper respiratory tract “the mucus is thicker and allows a successful clearance of the foreign bodies particles, in addition, the mechanical movement of ciliated epithelium [...] prevents smaller particles from spreading through the epithelium and reach the circulation. […] In the lower respiratory tract[, on the other end,] the mucus layer is thinner, thus facilitating the diffusion of particles which […] are [then] able to reach this part of the respiratory tract. Once penetrated, the MPs can spread into the general circulation by cellular uptake or diffusion” (P).
So, all in all, as for the respiratory system, according to the Italian Brains, the MPs probably enter the bloodstream mainly, or at least more easily, via the lower respiratory tract.
Now, dear listener, let’s go to what is, in Dr. Ragusa and colleagues’ educated guess, the second probable gateway used by MPs to infiltrate your body: the gastrointestinal system.
Ok, first step: a human being somehow ingests MPs. Aaaand weee’ll fully delve into the “eating plastics” issue next time, but I can already tell you this now, as an appetizer (hahahha, see what I did, eh!? You see what I did?): it has been found, for instance, that in “commercial mussels [(that is in mussels “consumed as food by humans” (1))] from Belgium, the number of microplastic particles varied from three to five fibers per 10g of mussels” (fibers as in synthetic fibers, that is made of plastics) (1), and “microplastics [have been] found in [two species of mussels] from five European countries (France, Italy, Denmark, Spain and The Netherlands)” (1).
Puzzling hu?! Well, dear listener, know this: “the potential for human ingestion of [plastic] fibers resulting from domestic dust during a meal may be higher than [plastic] fiber intake through consumption of [contaminated] mussels”, (1).
So, pal, apparently when one bites the dust, well, that one is biting a lot of plastics too...
Anyway, step one of the microplastics’ gastrointestinal system way to the human bloodstream (and ultimately even to the placenta): a human ingests microplastics and these microplastics reach the intestine.
Aaand the lymphoid organs are those organs that, along with a bunch of tissues and cells, form that life-saving thing, located throughout your human body, called immune system.
Now, at the level of the just mentioned Peyer’s patches, the ingested microplastics are probably taken up via endocytosis by the M cells.
Soo, let’s refresh the concept of endocytosis, shall we?
Aaas you know, dear listener, the cell membrane forms the boundary of cells, and it is a “complex and dynamic structure” (see) which is a “selectively permeable lipid bilayer that contains many proteins” (see). Given that, endocytosis is the production of brand new internal membranes from cell membrane, so that, in “so doing, plasma membrane lipids and integral proteins and extracellular fluid become fully internalized into the cell” (2).
Now, pal, you are probably so fed up with all these explanations that you’re thinking of quitting listening this episode/reading this post, and starting investing all your money in the space industry so that the colonization of the asteroids belt will become a reality and you can move far far faaar away and just put your mind into less troubling questions such: “I wonder if the oxygen reservoirs will last till next refueling… Oh, well, first things first, let’s try and remember the code to open this hatch and reenter the shuttle”.
I feel you bro/sis, really.
But be just a bit more patient. We’re getting there.
So, microplastics are probably taken up via the just explained endocytosis by the M cells.
Aaand M cells (aka microfold cells) are cells “found among the epithelial cells covering Peyer's patches in the intestine” (see) that “take up and transport a wide variety of sizes and types of intestinal […] microorganisms” and antigens, (see) like, precisely, microplastics [(given the times, for sure you don’t need a definition of antigen)], “from apical surfaces of the [inside space of the intestine, aka the] intestinal lumen[,] to the underlying immune system” (see) components, like the dendritic cells, that are exactly immune cells.
So, in short: so far you human ingest plastic, plastic gets to the intestine, there the M cells kinda eat it up and then kinda spit it out to some immune system cells called dendritic cells.
These dendritic cells take the load coming from the M cells, that is, in our case, the microplastics, and then they transfer them into the lymphatic circulation, that is the circulation of the lymph through the lymph system.
The lymph system “is a major part of the body's immune system [and it] is a network of organs, lymph nodes, lymph ducts, and lymph vessels that make and move lymph from tissues to the bloodstream. [The lymph] is a clear-to-white fluid made of: [w]hite blood cells, especially lymphocytes, the cells that attack bacteria in the blood[, and by fluid] from the intestines called chyle, which contains proteins and fats” (see) and, in our case, as just said, probably microplastics too.
Oook, folks, to super sum up: the microplastics are ingested, reach the intestine, there, via endocytosis by cells called M cells, the MPs are passed to immune cells called dendritic cells, from them they go to the lymph system, and from the lymph system our pertinacious traveling microplastics finally reach the bloodstream.
|Grastrointestinal system & microplastics (by @sciencemug)|
Buuut, dear listener, there’s another way, the Italian Brains say, through which the microplastics, once in the intestine, manage to make a trip into the bloodstream, a way that doesn’t involve the endocytosis performed by the mighty M cells.
Aaand this alternative way is called: the paracellular transport.
Now, paracellular transport is not a type of stuff movement done by some cells with a peculiar X chromosome that have freaky ribosomal paranormal powers like reading the mitochondrial thoughts of other cells or creating micro-hurricanes in the cytoplasm of evil bugs.
Nope, dear listener.
Paracellular transport is “the passage of molecules between adjacent epithelial cells” (see) that, in our specific case, are the intestinal epithelium adjacent cells, cells which are “joined together by junctional complexes” (see).
Dr. Ragusa and colleagues, indeed, think that the MPs can exploit loose junctions at this level to cross the intestinal lumen. The ITBs also add that this “phenomenon could partially explain why some inflammatory states, which increase loose junctions[,] favor intestinal passage” (P).
Once in the intestinal lumen, then, the microplastics meet the above mentioned dendritic cells which transport them into the lymphatic circulation and, as just said before, from there they reach the bloodstream and eventually the placenta.
Ok, folks, let’s make a giant super concise recap of the gastrointestinal microplastics' pathway: a human being somehow gulps down microplastics. The MPs go to the intestine; there, the MPs are transferred to the lymphatic system; once in that circulation, the microplastics finally reach the blood, and it is via bloodstream, in the case the human ingesting them be a pregnant woman, that the microplastics eventually reach even the placenta.
Sooo, dear listener, to super super sum up aaaall the possible microplastics’ trip scenarios pictured by the Italian Brains let’s say this: microplastics can reach the placenta, and the inner organs of the human body in general, most probably via bloodstream, where they end up after being breathed in and/or ingested.
Ok, dear skeptical listener, at this point you could say: “oh, ‘cmon dude, big deal, you know that more than 90% of the ingested plastic goes away when you go number two!” (3).
Well, yup buddy, you humans get rid of the great majority of plastics via feces, sure, but that ain’t true for plastics smaller than 150μm (3), and I remind you that the ones we are talking about here are 5 to 10μm big, so pretty smaller than 150μm.
Besides, pal, were I a human-being like you are, well, even a 10% of plastic not flushed out from my system would be anyway a great great deal of concern to me!
‘Cause, dear listener, plastics in the placenta, and in the human body in general, are dangerous.
Aaaaand, folks, you’ll find out why, how specifically, and how much in the next and final part of this episode/post!
In the meantime, people, take care, and if you spare some time and feel like doing it, please subscribe and/or rate this podcast, and/or leave a comment on the blog, and/or take a tour on my stuffngo (sNg) e-shop on zazzle.com so you can see if there’s something you like, aaand/or make a donation clicking on the “Donate” button on this dumb blog’s home page!
The paper this post is about (P)
P - Ragusa, A., Svelato, A., Santacroce, C., Catalano, P., Notarstefano, V., Carnevali, O., Papa, F., Rongioletti, M.C.A., Baiocco, F., Draghi, S., et al. (2021). Plasticenta: First evidence of microplastics in human placenta. Environment International 146, 106274.
1 - Barboza, L.G.A., Dick Vethaak, A., Lavorante, B.R.B.O., Lundebye, A.-K., and Guilhermino, L. (2018). Marine microplastic debris: An emerging issue for food security, food safety and human health. Marine Pollution Bulletin 133, 336–348.
2 - Doherty, G.J., and McMahon, H.T. (2009). Mechanisms of Endocytosis. Annual Review of Biochemistry 78, 857–902.
3 - EFSA Panel on Contaminants in the Food Chain (CONTAM) (2016). Presence of microplastics and nanoplastics in food, with particular focus on seafood. EFSA Journal 14, e04501.