The problem isn't just the plastics themselves. Plastics are chemical "sponges" that will soak up pollutants over time from the environment (brominated fire retardants, bisphenols, PBCs, pesticides, phthalates, heavy metals, etc) and deliver them in a concentrated dose into the body.
Even if plastics of all sizes are 100% biologically inert, they're still a Trojan Horse for other toxins.
These porous polymer powders consist entirely of microscopic little sponges where they soak up and/or leach out all kinds of chemicals more so than the plain polymer, and with different affinity too.
However, even when common waste plastic particles themselves are not microscopically porous, different plastics soak up different chemicals to different degrees depending on what type of contact they come into. For instance kilos of polyethylene nurdles floating in the water will actually become "soaked" with some hydrocarbon liquids that are also floating or dissolved in the water. Even physically softened. These are very solid pea-sized beads that are not micro-sized plastics at all. They would have to degrade a whole lot before they fall into the micro category. And they are not manufactured to intentionally have a nano-porous structure like the finer mesh porous polymer powders.
Chemicals and plastics just don't go away so safely every time.
>Roughly 50% of indoor dust is composed of microplastics, so it's not like it's uncommon.
I highly doubt that. Soil, skin and pollen are usually the big ones. Hairs depending one how you count dust, but eliminating hair like fibres would also eliminate most of the sources of plastic, unless you allow really large particle sizes.
[edit] Checking research. The highest claim I found was 39% of fibres (in household dust, Japan). but that seemed to be per particle not by volume.
Synthetic fibers from clothes are microplastics, and clothes shed lots of fibers. Not to mention all the upholstered furniture, carpet, rugs, drapes, bags, etc.
Thanks and noted, I'm happy to accept your figure. Even at 40% by number density that still means microplastics are hardly rare. I don't need to nitpick the exact number.
It was just an aside anyway. My main point is that MPs are vehicles for toxins, which addresses the original question about how (supposedly inert) microplastics can cause harm.
Thanks again for setting me straight, I must have misremembered.
It's good to keep in mind that there are a very broad range of figures. The Japan one was just the highest I could find with a quick search.
I like this study https://link.springer.com/article/10.1186/s12302-019-0279-9 not so much because they give a definitive answer, but the provide a much better sense of the nuance that bold claims miss. It's too easy to make a bold claim of a number that seemingly contradicts another similarly bold claim. The nuanced approach can often reveal that both bold claims are, in fact, true but not meaningful because they lose significant context.
For example, a lot of reports on water use neglect locality of the use. What the term 'use' means (how much water does a hydroelectric dam use, is that the same sense of use as irrigation?), is there scarcity where it is used? Is it the same class of water as the water in demand (potable / brine / etc.)
The haphazard use of terms has resulted in an insane range of claims of water use per AI query (or lithium mined, or tomatoes grown). The lack of faith leads people to assume one party is lying, but often all of the numbers are accurate in a kind of way. Just not comparable and sometimes not even meaningful
I see you still don't say microplastics are rare. Violently agreeing with each-other, it seems. ;)
Synthetic textiles (clothes, upholstery, carpet, dryer exhaust, washer drainage) are of course the biggest culprits, with most of that trapped indoors with us, or co-located with human activity. If you have a dog that may change the mass fraction, but the MP exposure remains the same (or worse due to additional wear).
Road and tire wear is the other big contributor, again co-localized with population density. That's one of those nuanced cases, because a large fraction of the tire mass is actually natural rubber. The synthetic additives make it categorized as 100% plastic, but this may not accurately reflect reality in terms of the chemistry or hazard-based analysis.
One of the sources of intentionally manufactured microplastics are known as porous polymers in fine mesh sizes.
This is over a $1 billion market and growing.
One of the pharmaceutical uses is precisely as a medium to deliver oral medications in a time-release way.
https://www.linkedin.com/pulse/porouspolymer-bead-real-world...
These porous polymer powders consist entirely of microscopic little sponges where they soak up and/or leach out all kinds of chemicals more so than the plain polymer, and with different affinity too.
However, even when common waste plastic particles themselves are not microscopically porous, different plastics soak up different chemicals to different degrees depending on what type of contact they come into. For instance kilos of polyethylene nurdles floating in the water will actually become "soaked" with some hydrocarbon liquids that are also floating or dissolved in the water. Even physically softened. These are very solid pea-sized beads that are not micro-sized plastics at all. They would have to degrade a whole lot before they fall into the micro category. And they are not manufactured to intentionally have a nano-porous structure like the finer mesh porous polymer powders.
Chemicals and plastics just don't go away so safely every time.