[nritchie]

This is why it is good lab procedure to always "run a blank." A blank is simply a sample that is constructed exactly like a real sample but without the thing you are studying. This way you quickly learn about contamination from tools/gloves/environment etc.

[crazygringo]

If microplastics are everywhere in flesh/brains/etc., how do you construct a blank without them? Isn't that the very issue here?

[godelski]

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]

> 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]

  > 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]

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.

[godelski]

  > Just so you know, the tone of your comment is extremely off-putting.

Didn't mean too, but if we're speaking about tone then it's worth noting you're being overly defensive. When you were trying to seek clarification you're approaching it in a combative way. As if from the stance that you're right and I'm wrong. I'll admit my patience quickly thins when talking on the internet as I just don't want to argue.

Also, you're well known here (why I'm responding now) and I think that also makes it important that you help set the culture here. To act in good faith like the guidelines illustrate. I'm not accusing you of arguing in bad faith (there's a lot of middle ground) but you should take just a few more seconds to consider an alternative interpretation (e.g. if your instinct was to interpret my ask for stronger good faith as an accusation of bad faith then you interpreted as the weakest version rather then the strongest)

I have a point here. It is that nuance and small details matter.

  > I don't have the slightest idea why you're rudely telling me "don't make assumptions"

I'm sure I could have said it better, by my tone was neutral. I'm not a LLM, and I'm not going to preference everything with "brilliant" or "great question", I'm just going to respond. *I'm not calling you dumb*, I'm just pointing out your error.

The problem with your understanding is that you are making erroneous assumptions. This needs to be pointed out to get you unstuck.

In science it's all about assumptions. People frequently throw around the term "from first principles" but you don't really hear that from scientists. First principles are hard to find. You derive them. Your first principles are your axioms. Your assumptions. They always exist, explicitly or implicitly. The problem is you probably didn't recognize you were making assumptions. That's fine though, because it's common. It's hard to avoid.

  > If you don't have helpful answers

You're right. But the thing is I was being helpful. Maybe not in the way you wanted, maybe not optionally, but I'm human.

  > You don't need to ... add a bunch of rude sentences while you do it.

I didn't.

Theres no name calling.

There's no attack.

There's not even an implication that you're dumb.

I did assume you don't have a PhD in chemistry or biology, but I'm pretty confident given your question (was I wrong?). I also said I don't have that qualification (but I do have lots of experimental science training) and that there were things I don't know either. So if you interpreted me as calling you dumb for not having that background then you need to recognize I would have been saying that about myself too! And that you didn't need this comment to infer that.

  > Better to just not reply at all.

Maybe. But that could apply to your own comment. You wrote yours to try to resolve things, right? That's why I left this comment too. But it's up to you how you interpret it.

[BlarfMcFlarf]

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

[crazygringo]

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.?

[vel0city]

> 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]

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.

[vel0city]

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]

  > 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]

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

[vel0city]

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]

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

[thephyber]

The point isn’t to have 0 microplastics according to the test.

The point of the blank is to identify the base level given the current testing environment. Then you test again with the variable.

If the majority of the microplastics contaminants were introduced in the blank, the variable would show minimal, if any, bump.

[fercircularbuf]

I don't believe the point is to construct a blank without them. Rather, the point is to capture what is already there (contaminants) so you can calibrate during the real sample.

[margalabargala]

Exactly.

If you run a blank and it has no fewer microplastics than the thing you are studying, then that tells you something.

[timr]

Well, in this case, it tells you that you may have contaminated the sample with your lab setup.

[SarahC_]

That's EXACTLY what the blanks for! It lets you see what to expect with "All things being the same - just not with the sample in place."

You sure you're a coder?

[bn-usd-mistake]

> Be kind. Don't be snarky. Converse curiously; don't cross-examine. Edit out swipes.

https://news.ycombinator.com/newsguidelines.html