Author: chogan@directresearch.com

 

Intro:  Not a lot of answers in this post

Seems like every week I read another story about microplastics. 

At some point in all that reading, it dawned on me that I didn’t actually know what microplastic is.  Sure, micro meaning small, and plastic, meaning plastic.  But that’s as deep as my understanding went.

Turns out, there are good reasons for my confusion.  The term “microplastic” is used for everything from shreds of plastic you can see, down to nano-scale bits that you’d need an electron microscope to see.  From the plastic chips left over from recycling, down to aerosol-sized microscopic fibers.  The microplastic in your tap water (fibers, mostly polyester) really isn’t the same stuff as the microplastic in your bottled water (particles, mostly bits of PETE or HDPE plastic).

Let me narrow down my interest to microplastic in my tap water.  Or maybe, microplastic in the air I breathe.

What’s that all about?  What is it, exactly?  How much is there?  Will my water filter remove it?  How about an air filter?  Is it harmful in the concentrations I’m routinely exposed to?

Weirdly, for something that seems to be in the news a lot, I could not find out much in the way of hard facts.  In this post, I at least begin to pin down why I’m not finding answers to those basic questions.

Other than the fact that my Brita water filter promises to remove most of it.  Whatever it is.  I think.

Source:  Brita.com, data for the “elite” filter, not their standard filter.

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First stop:  A mother lode of click-bait

The popular press on this issue yields a coherent if superficial story about the environmental danger of microplastic.

It’s invisible.  Municipal tap water, for example, typically contains bits of plastic that are too small to be seen with the naked eye. It is not present in enough density to give the water a cloudy or turbid appearance.  Nor does it affect the smell or taste of the water.

It’s everywhere.  These bits are too small to be filtered out completely by typical municipal water plants.  And once you start looking for it, you can find some amount of microplastic almost everywhere.  Not just tap water, but: Bottled water.  Bottled soda.  Even in things that are bottled in glass bottles.  Animal tissue.  Breast milk.  Rivers.  The oceans.  Fish.  The soil.  The air.  The clouds.

(Ah, yeah, in addition to eating and drinking it, you breathe it in the form of floating dust particles.)

It might be bad for you.  I haven’t yet come across hard evidence one way or the other, at levels seen by the average U.S. resident, but the most common analogy is with asbestos.  Exposure to asbestos fibers is associated with cancer presumably because the fibers were small enough to enter cells and perturb DNA replication.  A lot of microplastic is in the form of fibers, some of which are likely small enough to enter cells.  So this is a plausible if unproven concern.

And that combination makes it hard to sort fact from fiction.  Look at the phrases in red above.  In the internet-driven world, you know what means.  It means that “microplastic” is an ideal and practically inexhaustible source of  click-bait.  Between the people who make their living out of scaring you, and the people make their living out of mindlessly repeating stuff they gathered off the internet, let’s just say that the facts appear thin on the ground.

On top of which, everybody hates on plastic.  Even as we, collectively, use vast amounts of it.  So you’ve got some degree of  axe-grinding dressed as fact-finding, thrown into the mix.

To be clear, I’m not dismissing this as a threat.  This, even though our public health authorities don’t seem to have any handle on it.  But that has happened before (think, leaded gasoline).  Sometimes widespread harm is only understood well after-the-fact.

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Three things

Three things make me hesitate before I freak out over microplastic.

Thing 1:  It’s not as if plastic is a new thing.  We’ve been using lots of plastic, for a long time, here in the U.S., and world-wide.  Whatever-it-is that microplastic does to you, chances are that it’s been doing that to you, to a greater or lesser degree, all your life.

Up until COVID, U.S. life expectancy had been increasing consistent with its historical trend.  So whatever it is that plastic in the environment is doing to us, it’s small enough not to perturb that trend.  It doesn’t mean it has no effect, it just strongly suggests that the population-level health effects, at typical exposure rates, are likely small.

There needs to be one major caveat there:  Assuming it isn’t just slowly accumulating.  And we’re only now beginning to reap what we’ve been sowing for the past N decades.  Haven’t stumbled across any evidence suggesting that, so far.

Thing 2:  It’s not as if having harmful material in your air or drinking water is new, either.  For example, Virginia requires that all public water supplies are tested, and that those test results be made public.  So I know there’s lead in my drinking water, but the 90th percentile of water samples in my town showed 1.5 parts per billion, lead.  That’s low enough that I cross it off my list of things to worry about.  (Source: 2022 water quality report testing 2021 water, Town of Vienna).

Thing 3:  This is a newly-recognized potential health hazard, and that means that there are no answers to even the most basic questions.  This really wasn’t on the public-health radar screen a decade ago, near as I can tell.

Suppose, for example, you wanted to see the equivalent of the report shown above, but for the microplastic content of your local tap water.  How much is there, in parts-per-million or parts-per-billion, and does that exceed some safety threshold?   You would discover that:

• No, they don’t measure it that way (PPM or PPB).
• No, nobody routinely monitors for it.
• No, it’s not reported in the State-mandated drinking water reports that my Town must publish.
• No, there is no accepted safety threshold.
• No, there’s no hard evidence one way or the other for impact on human health.
  • Yet.

 

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Boiling down the basic background.

Believe it or not, I don’t get paid by the word.  So let me just state some key facts that I think I’ve learned, without citation as to sources, then cut to the chase regarding health effects.

1.  There is no standard definition of microplastic.  You’ll see that used for pieces of plastic that are anything from dime-sized to nano-scale bits (fractions of a micron).  But most research focuses on stuff that’s around the same size as aerosol air pollution, PM 10 (particles 10 microns or smaller) or PM 2.5 (particles 2.5 microns or smaller).   (Recall that a human hair is about 70 microns thick, and that aerosol particles — those that can remain suspended in the air for long times — are conventionally taken as those that are 5 microns and smaller).  The most common cutoffs I’ve seen for “microplastic” are 10 microns or smaller, or 1 micron or smaller.
2. There are no quantitative measures of it similar to “parts per million” for drinking water.  Instead, for liquids, they run the liquid through a fine filter and count whatever gets caught.  So the most common measure of quantity is “counts per liter”, as in, the count of microplastic bits found, per liter of water poured through the filter.  Big bits, small bits, chunks, fibers — it’s all the same in that measure.
3. It takes sophisticated equipment to determine how much plastic and what type of plastic is there.  Infrared spectroscopy, for most studies that I’ve seen.  Different types of plastic have unique infrared “signatures”.  Typically, certain distinct strong peaks in IR reflection or absorption are associated with specific common plastics.  At root, it’s the same process that your plastics recycler uses to sort plastic.  And the amounts in question are small enough that careful studies need to net out the residual or background amount of microplastic that’s found on everything, including everything in the labs that test for this stuff.
4. In water, it’s mostly fibers.  And those fibers are mostly polyester.  But that’s not because polyester is uniquely bad among synthetic fibers.  In fact, acrylic cloth and yarn shed microplastic fibers at a much higher rate than polyester.  But polyester shows up as the main contributor because we use so much of it.
5. The presumption is that this mostly enters the waterways from laundry effluent, but it may enter via deposition from the air as well.  Clothing sheds fiber as it is washed and dried, and it sheds as you wear it.  Plausibly, wearing it generates a much larger volume of shed fiber than washing it.  Some of that fiber remains suspended as dust in the air, which eventually settles and is then deposited in waterways via runoff.
6. Typical municipal water processing removes most but not all of it.  Of what I recall, raw water might typically have on order of 200 CPL (counts per liter) of microplastic, and the finished water might have on order of 5 CPL.
7. You also get little chunks of plastic that are not fibers.  Those also count, and my reading is that when you hear about microplastic in bottled water, for example, that’s what you’re hearing about. It’s not even clear that anybody knows where that comes from, but the presumption is that these are residues of some factory production process.
8. There’s enough of this in the environment that labs have to net out their background level of microplastic when they test for it.   Just as they would have to do if (e.g.) measuring radiation, because every place on earth is slightly radioactive.  The readings you see in most studies are not the “raw” counts, they are the counts from the samples tested, less the counts found on control samples, presumably reflecting the background level in the lab doing the counting. Any human-occupied environment — laboratory, factory, office, whatnot — is going to have some ambient level of microplastic fibers, as long as the people in it are wearing clothes, and those clothes contain synthetic fibers.
9. Most of it passes right through you.  At least, the larger fibers do.  That’s my takeaway from studies of fish that are fed materials containing microplastic fiber.  Mostly it just passes right through them.
10. But some does not.  The concern centers around the tiniest fibers (fractions-of-a-micron), that are presumably small enough to pass through the gut, into the blood stream, and then into your tissues.
11. I did not find research on what mechanisms the body has for breaking down or otherwise removing microplastic that make it past the gut/lungs.  So once you’ve absorbed some of this stuff, I have no clue how (or even, whether) you get rid of it.  That said, research seems to indicate that nylon fibers, in particular, produce some toxic byproducts when they break down in the body.
12. Jury remains out on whether or not microplastic cause significant harm to humans.  At typical environmental concentrations.  In a dust-filled factory, you bet that synthetic fiber dust causes lung injury.  My take on it is that there’s almost literally no credible research on the likely level of harm at typical environmental concentrations of microplastic, because this has only recently (past decade or so) come to the attention of public health authorities.

A few observations.

First, taken as a whole, this likely explains why nobody routinely tests tap water for it. There’s no standard definition of it.  There’s no hard evidence of human harm, let alone some agreed-upon maximum threshold for safety.  It takes specialized equipment and techniques to measure.  And there’s a good chance of contamination from the testing lab.

Second, there’s some obvious potential for mischief in reporting the presence of microplastic in (fill-in-the-blank), in that this stuff is everywhere.  That is, there’s going to be a background level of microplastic in any testing lab.  If you don’t net that out, you’ve got the potential to report finding microplastic in pretty much anything you care to test.

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Where to start:  Is there a synthetic-fiber analog of brown lung?  Answer:  Yes.

That is, do factory workers get sick from breathing in high levels of synthetic fibers?

Historically, workers in cotton mills suffered from a high incidence of brown lung.  This was the result of chronic exposure to high levels cotton dust, or to the dust of other organic fibers (jute, hemp, and so on.)

Is there anything to suggest that the same thing happens with chronic exposure to high levels of fragments of synthetic fibers?

Short answer: Yes, starting with Flock Workers Lung (.pdf).  This was recognized around the year 2000, in workers in Massachusetts plants that produced nylon flocking for use in producing velour-type fabrics.  In those plants, long nylon fibers were chopped into short lengths.  Inhaling airborne nylon fiber fragments led to inflammation, reduced lung function, and asthsma-like symptoms.

Whether polyester fiber fragments increase risk of lung cancer in factory workers is still an open question.  One study of a quarter-million female textile workers in Shanhai, China found no association between synthetic fiber exposure and cancer (reference).  By contrast, a study of one large industrial plant in France found that greater exposure to fiber dust was associated with increased risk of developing lung cancer (reference), but the dust was from a mix of fibers, including asbestos.

The upshot of this is that heavy exposure to large amounts of airborne synthetic fibers can mess up your lungs fairly badly.  This is definitely true for nylon, and may be true for other synthetic fibers.  (Several studies suggest to me that nylon fibers are particularly noxious, for reasons that appear related to what they release as they break down.)

This should come as no surprise, as chronic exposure to large amounts of almost any type of dust causes lung problems.  Sometimes the diseases have names, such as black lung for coal dust, mesothelioma for asbestos, siliconiosis (sp?) for silicon dust, and so on.  Sometimes, fiber will damage the lungs, but there is no specific name, for example, damage caused by breathing wood dust in a woodworking environment.  Name a dust, and an excess probably causes problems.  Toner?  Yep.  Fiberglass?  Yep.  And so on.

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Is there any epidemiological evidence for the effect of lower levels of exposure?

No.   Not that I found. 

First, it’s a good bet that most people will have some microplastic in their lungs.  One small study in London (reference), using lung tissue samples that had been removed from people for various reasons.  It looks like they found a small number of microplastic particles in every sample they tested, although the number was not hugely higher than the background rate in the test lab.  By contrast, another study (reference) found 24 microplastic fibers total, in a sample of about 100 bits of lung tissue, but those fibers were more likely to be found in tumors than in normal lung tissue.

But in terms of linking population-level exposure to disease rate, I haven’t seen much.  And the studies of factory workers suggest why.  Where there appears to be an association between synthetic fiber exposure and cancer, say, we’re talking about modest increases (50% higher risk) for relatively rare cancers.  If the massive exposure you’d get from working in a textile mill has only a modest impact, you may not be able to see much impact from the vastly lower exposure of the general population.

That said, there are some hints.  There was a nice in-vitro study where polyester fibers inhibited the healing of lung “organoids”.  And one of the studies of lung tissue found that plastic fibers were more likely to be found in lung tumors than in healthy lung tissue.

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Addendum:  Water filtration versus air filtration.

This is just a note-to-self that I now need to look up how water filtration works.

With COVID, I got up to speed on how air filters and N95 masks filter out aerosols. It’s not at all obvious, and it’s nothing like passing material through a fine-mesh filter.

For example, the hardest particle to capture is about 0.3 microns.  That’s why N95 masks are rated as producing a 95% reduction in 0.3 micron particles.  They actually produce a greater reduction in particles both larger and smaller than 0.3 microns.

I’m pretty sure that water filtration cannot possibly work the same way.  For example, 3M Filtrete material takes advantage of Brownian motion of particles in the air, in order to bring the most difficult-to-capture particles (0.3 micron) into contact with the electrostatically-charged filter material.  Well, that’s not going to work in a dense fluid like water.  Brownian motion won’t move particles far enough.

But I just plain don’t know.  For example, the Brita filter at the start of this posting is rated for capturing particles in the 0.5 to 1.0 micron (micrometer) range.  Is this like an air filter, so I can be assured that it captures even higher percentages of particles larger and smaller than that?  Or does that mean it simply doesn’t capture particles below 0.5 microns?

I just have a hunch that if you poured water through an N95 mask, it wouldn’t filter the water.  But I need to get up to speed on the basic science.