Here's a very naïve example to help illustrate how you can do a "blank" (a control).

Say you're testing a sample of water in a test tube. Repeat all steps in exactly the same way, but use distilled water. You can even do all the steps and use no water! (Including having an empty container and pouring nothing from the empty container into the test tube).

By doing things like this you create samples that allow you to look for contamination. How do you know that the thing you're testing has microplastics? (Or whatever) because it has more than the blanks/controls. That's it. Congrats, you've isolated a variable in your experiment.

Btw, this is pretty common practice. In fact! Here's a video of someone doing exactly that "nothing" control looking for microplastics. Those steps are done at 10:20.

https://youtube.com/watch?v=oDDQjEpuFfQ

▲ crazygringo 2 days ago | parent | next [-]

> Repeat all steps in exactly the same way, but use distilled water. You can even do all the steps and use no water!

This is where I get lost. Maybe I don't understand what a blank is.

If you have access to distilled water that you have excellent reason to believe is free from what you're detecting, then great. But my point is we don't have access to animal flesh guaranteed to be free of microplastics, do we? Because they're everywhere in the environment.

And if you use no water at all, it seems like you're missing the entire vector of contamination from acquiring and transporting the water. E.g. if the water container is producing contamination, then your blank of no water isn't revealing the source of contamination! The blank isn't helping at all.

I don't have any issue with the concept of a blank sample when they're feasible. My issue is, I don't see how you can produce a blank sample of animal tissue without microplastics specifically because microplastics are everywhere in nature, and I don't see how a slide with zero animal tissue at all is a useful blank.

▲ godelski 19 hours ago | parent | next [-]

  > If you have access to distilled water that you have excellent reason to believe is free from what you're detecting

Don't make assumptions.

  > we don't have access to animal flesh guaranteed to be free of microplastics, do we?

Don't make assumptions.

These two assumptions could potentially be at odds.

  > And if you use no water at all, it seems like you're missing the entire vector of contamination from acquiring and transporting the water.

Don't use water? Use another liquid that doesn't interact the same way. I gave examples, they are clearly non-exhaustive.

I don't have an answer for you for the exact process but I'm also not a scientist working on these experiments. But the people who are doing the experiments are. They know the answers to these questions. A lot of it is going to be detailed in the papers but some won't be because it's more common knowledge among the niche, but you'd likely learn it if you pursued a PhD in the domain

	▲	crazygringo 15 hours ago \| parent [-]
		Just so you know, the tone of your comment is extremely off-putting. I don't have the slightest idea why you're rudely telling me "don't make assumptions", especially if you don't have additional information to add. And the suggestion to "pursue a PhD in the domain" if I want answers is exceedingly obnoxious. If you don't have helpful answers, you don't need to leave a comment. You don't need to say that you don't have answers but add a bunch of rude sentences while you do it. Better to just not reply at all.

▲ BlarfMcFlarf 2 days ago | parent | prev [-]

It doesn’t have to be an identical material, just one that has similar properties in attracting and holding contaminants.

	▲	crazygringo 2 days ago \| parent [-]
		So if you're studying slices of e.g. brain to look for microplastic particles, what would be a material with similar properties, that you would then go through the same steps of preserving, preparing, slicing, mounting, etc.? I'm genuinely curious. Are there standard widely used stand-in materials for animal flesh, for plant materials, etc.?

▲ 2 days ago | parent | prev | next [-]

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▲ vel0city 2 days ago | parent | prev [-]

> Repeat all steps in exactly the same way, but use distilled water.

But how do you know your source of distilled water isn't also contaminated?

▲ mattkrause 2 days ago | parent | next [-]

The point is that blank lets you measure that level of "background" contamination, which you then use to correct the measurements made on actual samples.

Suppose you measure around 100 plastic particles per unit in your blank and 1000 in a sample of A. This suggests that A enriches (sheds, etc) microplastic particles. On the other hand, if you found (say) 101 particles/unit in a sample of B, you'd conclude B doesn't do that.

▲ 2 days ago | parent | next [-]

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▲ vel0city 2 days ago | parent | prev [-]

But in your example you still don't know if it was your testing process that shed 100 plastic particles or if your distilling process shed 100 plastic particles, meaning you don't actually know if B was or was not the source of the plastic particles. Was it your testing process that introduced those 100 particles, was it the distilling process that introduced them, 50/50, or something else?

B would be inconclusive against what you'd hope to be some kind of background, as its not significantly more but one couldn't conclude the source didn't shed that 100 because you don't actually know if in the blank the 100 particles of contamination was definitely your testing process or the source material genuinely having 100 particles of contamination.

I do agree though, in the A case one could pretty easily conclude whatever generated that sample is adding way more particles than an attempt at a baseline/background.

	▲	godelski 19 hours ago \| parent [-]
		`> B would be inconclusive against what you'd hope to be some kind of background` Correct. And this is why scientists use null hypothesis testing. You disprove things in science, not prove them. I think that's why you're confused. In the first situation you disproved that it comes from the background

▲ godelski 2 days ago | parent | prev [-]

You continue reading the comment and use the other version of a blank

▲

vel0city 2 days ago | parent [-]

So why even bother mentioning the distilled water? And if you're testing an aqueous process don't you pretty much need some fluid to put through the process?

	▲	godelski 20 hours ago \| parent [-]
		I gave the second example to try to avoid this type of response. It's not that hard to grasp. You don't need some fluid