Airborne Microplastics

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MichaelG.
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Airborne Microplastics

#1 Post by MichaelG. » Thu Oct 21, 2021 9:31 am

The quoted numbers are still mercifully small … but the paper linked in this story is interesting; and perhaps should prompt further investigation by we amateurs:
https://theconversation.com/plastic-pla ... obe-168787

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A new study published this year has found microplastics in soils collected from sand in the Kavir and Lut deserts of Iran, with an average abundance of about 0.02 microplastic particles per gram of sand. Given little evidence of any large plastic objects in these areas, the particles were probably deposited in the desert by the wind.
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Re: Airborne Microplastics

#2 Post by microcosmos » Fri Oct 22, 2021 3:51 am

Thanks for the alert. It's really interesting to me as it combines the microscopical exploration of both soil and microplastics.

I see from the abstract (I can't access the full text) that they used micro-Raman spectroscopy and SEM to identify and characterize the synthetic fibres in the soil. They probably observed them using an optical microscope as well, since that's probably what the Raman apparatus would have been attached to.

For amateurs, I think a polarizing microscope alone can already identify the fibres through their birefringence value (derived from the interference colour and the diameter or thickness which is easy to measure using the eyepiece micrometer). If more precision is needed, one can use de Sénarmont or Berek compensators to precisely measure the retardation of the fibre. The advantage of using the specialized compensators is that one can accurately measure the retardation even if there is any colouring dye in the fibres that obscures their true interference colours.

I will find a chance to explore this one day!

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Re: Airborne Microplastics

#3 Post by MichaelG. » Fri Oct 22, 2021 8:16 am

Glad to see it’s of interest

Unfortunately; the terms of my access do not permit me to share the document … but I am hopefully permitted brief quotation:
.
■ RESULTS

Examples of MPs retrieved from the desert soils and as viewed under the binocular microscope are shown in Figure 2. The majority of particles were fibers of varying lengths, thicknesses, and colors that were often coiled or twisted. Of the 21 MPs retrieved from Kavir and Lut soils and analyzed for polymeric makeup by μ-Raman spectroscopy (and comprising 18 fibers and three fragments), 11 were identified as PET, seven were Nylon, two were polystyrene, and one was polypropylene.

Under the SEM, and as exemplified in Figure 3, the surfaces of some of the fibers examined appeared smooth but with adhered particulates returning EDX peaks (e.g., Al, Ca, Cl, Fe, Mg, Ti, Zn) characteristic of soil and, possibly, residual salts (including ZnCl2) that formed during sample processing. Other fibers, however, along with fragmented MPs, appeared to have undergone significant and heterogeneous weathering and fragmentation, resulting in surfaces that were rough and irregular and, in some cases, pitted and notched, but that still contained evidence of adherent or trapped soil particulates. A summary of the numbers and types of MPs identified in the 300 g soil samples collected from the different locations and geomorphological features in the Lut Desert in September 2019 is given in Table 1. There were 67 MPs in total, with fibers dominating shape or form (96%) and the three nonfibrous MPs classified as fragments. Features with the greatest numbers of MP were the hillsides of the yardangs and two out of the four moving sands. Moreover, yardang hillsides and moving sands were the only features where MP fragments were observed …
8450B98A-CC9A-4D38-B949-8DE5F3FA3197.jpeg
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.

As I first mentioned … these appear to be mercifully small quantities
I would also hypothesise that the SEM results may also indicate that the moving sands are doing a good job of grinding-up the micro-particles. … But is that a ‘solution’ or just another aspect of the problem ?

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Re: Airborne Microplastics

#4 Post by microcosmos » Fri Oct 22, 2021 8:50 am

Thank you for the screenshot and quotes - nice to see the micrographs and some of the detailed findings.

Just as a thought experiment, if I were to go out and collect soil samples for a similar analysis, one of my first problems would probably be how to identify the microplastics in the soil. If it is a scientific study, I will have to identify all the microplastics, not just those that I can easily pick out. I guess I would need to explain how I ensured that the sampling wasn't biased towards fibres.

The fibres are relatively easy owing to their shape, but the more spherical/irregular microplastics would be trickier as they blend in with the natural soil particles. They probably explained it elsewhere in the paper, but if I were doing this then I would be wondering whether illumination methods like bright-field or dark-field would be suitable (by detecting the different transparency and smoothness of the microplastics from the soil particles), or whether polarization is needed for detecting the undulose extinction of manufacturing strain in the plastic.

Would AI help? Perhaps the software could use object segmentation to identify the soil particles and then further identify their optical properties. This could give a more rigorous/objective analysis and much larger sample size for statistical analysis than doing it by eye. I think Zeiss and probably Leica already has software that can be adapted to this application, while Nikon and Olympus' AI software are more tuned to life sciences I think. Or an amateur microscopist could programme his/her own neural network. But there's also the challenge of having enough training data.

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Re: Airborne Microplastics

#5 Post by EYE C U » Fri Oct 22, 2021 10:03 pm

i have micro plastic spheres all over the place..all that spray paint dust.

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Re: Airborne Microplastics

#6 Post by microcosmos » Sat Oct 23, 2021 2:18 am

EYE C U wrote:
Fri Oct 22, 2021 10:03 pm
i have micro plastic spheres all over the place..all that spray paint dust.
Are they considered plastic? What do they look like under the scope? Do they require reflected light (if some of the ingredients are opaque oxides etc.)?

Interesting. I wonder how widespread micro-paint pollution is. We use millions of litres of paint and painted things get weathered all the time.

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Re: Airborne Microplastics

#7 Post by EYE C U » Mon Oct 25, 2021 12:33 am

ACRYLIC PAINT IS PLASTIC BASICALLY...IF THE DRIED IN THE AIR, AND MOST DO YES THEY ARE ROUND...

TRY SQUIRTING SOME SPRAY PAINT 6 FY OVER A SLIDE AND SEE

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Re: Airborne Microplastics

#8 Post by microcosmos » Mon Oct 25, 2021 2:11 am

EYE C U wrote:
Mon Oct 25, 2021 12:33 am
ACRYLIC PAINT IS PLASTIC BASICALLY...IF THE DRIED IN THE AIR, AND MOST DO YES THEY ARE ROUND...

TRY SQUIRTING SOME SPRAY PAINT 6 FY OVER A SLIDE AND SEE
As you already have lots of spray dust at your place, it would be great if you could post some micrographs when you have time - if they're acrylic maybe they're transparent and will show strain polarization, although the pigment in the paint may mask the interference colours or even make it opaque.

I don't have any spray paint at home and am not ready to buy a whole can to spray it all over my place just to make a slide :lol:

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Re: Airborne Microplastics

#9 Post by microcosmos » Mon Oct 25, 2021 2:25 am

Well I just found a collection of paint micrographs:

http://www.microlabgallery.com/results.htm?cx=001258474697822866463%3Awhoad_i24ri&cof=FORID%3A9&q=paint&sa=Search

There's a reference in one of the links - Crown, David A., THE FORENSIC EXAMINATION OF PAINTS AND PIGMENTS, Charles C. Thomas Publisher, 1968.

That website has lots more. I remember visiting it when I was replying to a thread on dispersion staining some time ago.

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Re: Airborne Microplastics

#10 Post by patta » Mon Oct 25, 2021 5:35 am

Experiment:
- clean carefully a slide;
- leave the slide outside, either in the house or on the terrace;
- after a couple of days, put the slide under the microscope, best if polarizing;
- wonder and surprise! thousands of micro-particles: dust, spores, fibers, plastic, sand... asbestos... airborne viruses... soot clogs... fried oil droplets... pollen...

Definitely interesting!
Last edited by patta on Mon Oct 25, 2021 5:49 am, edited 1 time in total.

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Re: Airborne Microplastics

#11 Post by microcosmos » Mon Oct 25, 2021 5:47 am

Thanks for the idea, I’ll try it! Do you know if there’s any kind of strain-free adhesive to make particles stick better and not get blown off the slide by wind?

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Re: Airborne Microplastics

#12 Post by patta » Mon Oct 25, 2021 5:56 am

Maybe a droplet of oil? Many particles will stick to it, then, a coverslip and it's mounted.

Or water: I have some buckets outside, it is marvelous to see that they don't get filled only by clean rainwater, but any sort of dirt; and then you find diatoms, ciliates, worms... where the heck they come from?
Spontaneous generation of life, had its reasonable grounds!

Other, a plastic slide, may keep particles adhering by electrostatic force.

Or "dust trap", protect the collecting slide with some walls, luke put it on the bottom of a tube.

Sorry far digression from the topic..

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Re: Airborne Microplastics

#13 Post by microcosmos » Mon Oct 25, 2021 6:40 am

Thanks. I think it's quite relevant to the topic, going by the title of it. Apologies if not - I started off this digression!

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Re: Airborne Microplastics

#14 Post by MichaelG. » Mon Oct 25, 2021 7:48 am

microcosmos wrote:
Mon Oct 25, 2021 6:40 am
Thanks. I think it's quite relevant to the topic, going by the title of it. Apologies if not - I started off this digression!
.

Plenty relevant enough for me ^^^

Most of us are unlikely to be sifting the desert sands … but we could, and should, be doing local research.

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Re: Airborne Microplastics

#15 Post by microcosmos » Sun Nov 14, 2021 5:57 am

It's been about three weeks since I put the slide out near the front door with a drop of olive oil, and I put it under the microscope yesterday.

There were particles and fibres although not very many, as Singapore is a city with relatively good pollution control of particles of optical microscopy size range.

I decided to do a quick revision of forensic microscopy on this fibre:

fibre.JPG
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Potentially useful characteristics for fibre identification that can be seen in bright-field include the colour, texture/scale patterns and internal structures (if any) of the fibre. Also the refractive index in the fast and slow directions, which needs to be measured using oils of different refractive index or using dispersion staining, which I'll have to come back to later.

The fibre appears to be of circular cross-section, given its mostly constant width (the thinning out you see above I think is due to damage rather than non-circularity), which is useful for calculating birefringence later. Using the calibrated eyepiece micrometer I measured the fibre diameter/thickness to be 13.5 μm.

By rotating the stage in cross-polarized light I determined that the fibre has straight extinction. This is a sometimes useful clue because some fibres, such as cotton, never go extinct due to their molecular structure.

I also grabbed the chance to use my Berek compensator. I had just taken it apart to make a design modification and reassembled/recalibrated it, so I was keen to put it through its paces:

Image

First, determining the sign of elongation, which helps narrow down the fibre possibilities. The fast ray of my Berek compensator is in the NE/SW direction (opposite to most fixed-wavelength plates) and the fibre's interference colours were subtracted when its length was parallel to that direction, so it's positive elongation (length slow):

Image

Most (but not all) fibres are positive elongation.

Next, I measured the exact retardation value, which is the really fun part of the Berek compensator that involves vernier goniometer readings, checking a table of values from the slide rule era and multiplying the preliminary result by the machine constant that is unique to each compensator:

fibre_retardation.JPG
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The calculated retardation value was 706 nm. This, with the measured thickness of the fibre, gives a birefringence value from the Michel-Lévy chart of around 0.048. This can be compared with the reference values of known fibres, which can be animal, plant or synthetic. Natural fibres tend to have higher birefringence than man-made ones, although there are overlaps.

Some of the information I give above came from this book:
Wheeler, B. P. 2021. Practical Forensic Microscopy: a Laboratory Manual 2nd ed. Wiley.

Another interesting reference:
De Wael, K. 2021. Microscopy in Forensic Fibre Examinations: a Practical Photo Atlas and Training Tool. Cobalt Blue Coaching.

As mentioned earlier I'm quite interested in the fact that it is possible to identify fibres using a simple optical polarizing microscope, without expensive facilities like Raman spectroscopy or SEM.

I have to move on to a more urgent project for now but I'll try to come back to this and analyze the other stuff on the slide.

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Re: Airborne Microplastics

#16 Post by MichaelG. » Sun Nov 14, 2021 6:07 am

Many thanks for the report and the links

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Re: Airborne Microplastics

#17 Post by crb5 » Sun Nov 14, 2021 4:09 pm

Here is our paper on detecting microplastics with basic microscopes. After a year's publishers embargo, it should now be downloadable for free at https://pubs.acs.org/articlesonrequest/ ... ZQ7PYDDMMW. You will likely need to register for ACS (American Chemical Society) but I do not have problems with spam from them.

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Re: Airborne Microplastics

#18 Post by MichaelG. » Sun Nov 14, 2021 9:58 pm

Thanks for the link, crb5 … but it appears that I can only register if I am already a member/subscriber :(

MichaelG.

.
Update: __ If this is the paper https://pubs.acs.org/action/showCitForm ... ed.8b00392
I managed to get it via the University Library :ugeek:
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Re: Airborne Microplastics

#19 Post by crb5 » Mon Nov 15, 2021 3:11 am

If this is the paper https://pubs.acs.org/action/showCitForm ... ed.8b00392
No, but it is the same journal. The reference is https://pubs.acs.org/doi/10.1021/acs.jchemed.0c00518

When you click on "Don't have an ACS ID? Create one today" the form asks for a Customer/Member number but there is no asterisk against this line, so you can leave it blank. You just need to say your are 18 years or older!

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Re: Airborne Microplastics

#20 Post by MichaelG. » Mon Nov 15, 2021 6:42 am

Ahh … Thank you

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Re: Airborne Microplastics

#21 Post by PeteM » Mon Nov 15, 2021 7:52 am

Here's another angle on airborne detritus - the impact on the productivity of solar cell arrays:

https://www.nature.com/articles/s41598-019-56868-z

The lead author hopes to crowd source a sort of global dust monitoring system. The same might be done with airborne plastics. We're now trying out an under $1K scope configuration including plan infinity Olympus optics, a modified stage to hold the sample coupons, a heads up display, and including the cost of a 15mp mirrorless camera. The images will to be fed to automated particle counting software.

FWIW, here's a darkfield image from one of their dust test coupons. 100x, single shot, no stacking. It should get a bit crisper once I get a remote release for the camera. The test slide is a thick low iron glass (as used in solar panels), 40mm x 40mm square, that's been left out to gather dust for a week or so:
.
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Dust_100x_darkfield2 reduced.jpg
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Re: Airborne Microplastics

#22 Post by 75RR » Mon Nov 15, 2021 11:49 am

PeteM wrote:
Mon Nov 15, 2021 7:52 am
Here's another angle on airborne detritus - the impact on the productivity of solar cell arrays:
Be interesting to see how 'Dust' is changing over time.

A scale bar on that image would be eye opening.
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Re: Airborne Microplastics

#23 Post by MichaelG. » Mon Nov 15, 2021 6:35 pm

PeteM wrote:
Mon Nov 15, 2021 7:52 am
Here's another angle on airborne detritus - the impact on the productivity of solar cell arrays:
.

That looks an interesting and useful project, Pete

Thanks for the link

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Re: Airborne Microplastics

#24 Post by MichaelG. » Mon Nov 15, 2021 7:07 pm

crb5 wrote:
Mon Nov 15, 2021 3:11 am
The reference is https://pubs.acs.org/doi/10.1021/acs.jchemed.0c00518
That worked fine, thanks
“Access through Institution”

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