Ordinary Lab Gloves May Have Skewed Microplastic Data
nautil.us140 points by WaitWaitWha 5 days ago
140 points by WaitWaitWha 5 days ago
I had strong echoes of a naieve lab experience in the 1970s: testing for organophosphates in seawater at the Forth Estuary was basically impossible except for gross amounts, because the standard analytical glass washing we used contaminated the glassware. You have to maintain a completely independent suite of glassware from pipettes all the way through to reaction vessels, and chromatography cells, and wash them with chromic acid, or special formulations.
(I don't work in this field any more, I was a lowly bottle washer and lab tech on a job creation scheme, I am sure the field has moved forward)
Similar issues plagued tests of iron concentration in seawater. Sample collection was contaminating the samples for years, until a procedure to collect a non-contaminated sample was developed by John Martin. He was able to finally figure out that actually most ocean water was iron deficient (that is to say: iron was the limiting factor in phytoplankton growth). Testing for environmental contaminants, especially in things that are commonly used by human civilization is really tricky.
People seem to be misunderstanding this paper. It doesn't claim that any previous papers have overestimated contamination. That would only happen if scientists didn't routinely use blanks as a comparison, which they do. E.g. "A procedural filter blank was created during each sample batch and analysed alongside the samples, to enumerate potential contamination that could have been introduced during the extraction process."
https://eprints.soton.ac.uk/476076/1/1_s2.0_S014765132300286...
This is an overstatement of the protection that blanks provide. As it says, they only (potentially) provide insight into contamination caused during the extraction process.
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.
If microplastics are everywhere in flesh/brains/etc., how do you construct a blank without them? Isn't that the very issue here?
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.
> 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.
> If you have access to distilled water that you have excellent reason to believe is free from what you're detecting
> we don't have access to animal flesh guaranteed to be free of microplastics, do we?
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.
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
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.
> Just so you know, the tone of your comment is extremely off-putting.
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"
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 don't need to ... add a bunch of rude sentences while you do it.
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.
It doesn’t have to be an identical material, just one that has similar properties in attracting and holding contaminants.
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.?
> 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?
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.
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.
> B would be inconclusive against what you'd hope to be some kind of background
I don't think I'm the one confused, as I'm not saying things like:
> On the other hand, if you found (say) 101 particles/unit in a sample of B, you'd conclude B doesn't do that
I'm fully aware of null hypothesis testing.
I interpreted that sentence as more casual language. Maybe I'm wrong to assume that. But I didn't write it either.
Either way, the difference didn't matter to answer your question. Them getting that part wrong doesn't make the other part wrong nor hard to understand.
> I'm fully aware of null hypothesis testing.
You continue reading the comment and use the other version of a blank
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?
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
So then maybe don't give the first if you know its a flawed example? Its not that hard to grasp.
> You don't need some fluid
Entirely depends on your testing procedure, and not something always true. Like in the video you posted he pretty much needs to have some kind of fluid through the process. Otherwise, he'd be missing out on contamination in the process of artificial mastication, running through the filtration process, etc. Sure, examine a dry and plain filter as well to see what the filters look like and ensure they're not just completely covered in particles as well, but you're then missing out testing quite a lot of the rest of the process.
> So then maybe don't give the first if you know its a flawed example?
> Its not that hard to grasp.
> Like in the video you posted he pretty much needs to have some kind of fluid through the process.
But if he used a different process he could have used it dry. There's a lot of ways to skin a cat. Different ways create different constraints.
So I'm confused here, did you just want to argue or did you actually want to understand? Because at this point it seems like you understand. And frankly, I don't want to argue