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That was the difficulty with DNA: how do you make that control if everything is contaminated and minor variations in protocol (like wafting your hands over the samples one too many times) changes the baseline?

It took years to figure out proper methods and many subfields have their own adjusted procedures and sometimes even statistical models. At least with DNA you could denature it very effectively, I’m not sure how they’re going to figure out the contamination issue with microplastics.

by gww9 hours ago|

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I have worked at a sequencing center before. DNA contamination is easier to mitigate because the lab disposables aren't made out of what you are testing. Disposables are almost always plastic and tend to have minimal DNA contamination. Environmental DNA contamination is largely mitigated with PCR hoods and careful protocols/practices. However, these procedures don't mitigate DNA contamination at the collection level, which is likely where the statistical models you mentioned help.

I can't imagine wafting your hands over the tubes would change the plastic amounts substantially compared to whatever negative controls the papers used. But again, I am not an expert on this kind of analytical chemistry. I always worry more about batch effects. But it does seem like microplastics are becoming the new microbiome.

by codebje10 hours ago|

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On the one hand, hundreds or perhaps thousands of studies might be wrong. On the other hand, this one might be wrong. Who's to say?

by estearum10 hours ago|

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Not even that! This study doesn't even say contamination is causing overestimation. It says that it's possible.

But as mentioned elsewhere in the thread, everyone knows that it's possible and take measure to mitigate it.

A paper that said those mitigations were insufficient or empirically found not to work would be interesting. A paper saying "you should mitigate this" is... not very interesting.

by xienze9 hours ago|

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> Not even that! This study doesn't even say contamination is causing overestimation. It says that it's possible.

From the article:

> They found that on average, the gloves imparted about 2,000 false positives per millimeter squared area.

I dunno, that seems like a lot of false positives. Doesn’t that strongly imply that overestimation would be a pretty likely outcome here? Sounds like a completely sterile 1mm^2 area would raise a ton of false positives because of just the gloves.

by estearum9 hours ago|

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The way you mitigate this is by using negative samples. Basically blank swabs/tubes/whatever that don't have the substance you're testing in it, but that is handled the same way.

Then the tested result is Actual Sample Result - Negative Sample Result.

So you'd expect a microplastic sample to have 2,000 plus N per mm^2, and N is the result of your test.

by throwup23810 hours ago|

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That has happened many times in scientific research. The aforementioned fad in DNA sequencing was one such case where tons of papers before proper methods were developed are entirely useless, essentially just garbage data. Another case is fMRI studies before the dead salmon experiment.