Completely incorrect. Overheating (aka "burning") completely destroys the molecule, and releases small molecule gases, like hydrogen fluoride. These have no relation to PFAS, they can't turn back into PFAS, and they look nothing like PFAS.

It's like saying that the smoke from burning wood is, in fact, wood.

And again, this has nothing to do with PFAS or PFOA. The principle cause is a complete breakdown of teflon into fluorinated small-molecule gases, such as hydrogen fluoride and tetrafluoroethylene. You're literally burning the coating off. It has as much relationship to PFOA as wood smoke has to wood.

...which has absolutely nothing to do with the PFOA that you might reasonably be concerned about. Teflon is chemically inert. It's literally used for human body implants. Teflon-coated pans are not your enemy. Fire-fighting foam, on the other hand -- you probably shouldn't bathe in it.

Any test that "detects" teflon in the generic category of "PFAS" is a hopelessly flawed test [1]. Unfortunately, a great many of these papers don't make the distinction, whether intentionally or due to incompetence, or simply because it's far easier to do that, and it gets better headlines.

[1] Important aside: historically, several of the major manufacturers of teflon had problems with PFOA contamination around the factories due to manufacturing processes. This is unrelated to your personal use of a Teflon pan, and also, the process has been changed. If you want to argue that the new process is also polluting, fine, make that argument -- but don't assert that the use of the final product is itself unsafe.

The dollar is trading pretty much at 30-year historic highs relative to all other currencies. You have to go back to ~2000 to find a stronger era, and then the 1980s before that.

https://www.marketwatch.com/investing/index/dxy

Comments URL: https://news.ycombinator.com/item?id=47597151

Points: 9

# Comments: 3

[1] https://www.multpl.com/shiller-pe

The entire point of a control is to test for that sort of contamination (or more generally, for malfunctions in the experimental workflow). In the case of a negative control, specifically, you're looking for an "positive" where one should not exist. If an experiment is set up such that you can obtain differential contamination in the controls but not the experimental arms, as you've described, then the entire experiment is invalid.

> What I was trying to say is that if the control is either mis-measured, for example by accidentally counting stearates as microplastics, or contaminated, then the summary outcome may underestimate or understate the prevalence of microplastics in the test sample, even though the measurement over-estimated it.

The control cannot be "mis-measured", any more or less than the other arms can be "mis-measured". You treat them identically, otherwise the control is not a control. Neither example you've given are exceptions: if the assay mistakes chemical B for chemical A, then it will also do so for the non-controls. If the experimental process contaminates the controls, it will also contaminate the non-controls.

What you're missing is that there's no absolute "correct" measurement -- yes, the control may itself be contaminated with something you don't even know about, thus "understating" the absolute measurement of whatever thing you're looking for, but the absolute measurement was never the goal. You're looking for between-group differences, nothing more.

Just to make it clearer, if I were going to run an extremely naïve experiment of this sort (i.e. detection of trace chemical contamination C via super-sensitive assay A) with any hope of validity, I'd want to do multiple replications of a dilution series, each with independent negative and positive controls. I'd then use something like ANOVA to look for significant deviations across the group means. This is like the "science 101" version of the experimental design. Any failure of any control means the experiment goes in the trash. Any "significant" result that doesn't follow the expected dilution series patterns, again, goes in the trash.

(This is, of course, after doing everything you can to mitigate for baseline levels of the contaminant in the lab environment, which is a process that itself probably requires multiple failed iterations of the experiment I just described.)

Most of the plastic contamination papers I have read are far, far from even that naïve baseline.

This paper used “light-based spectroscopy” [1]. Many others use methods that depend on gas chromatography or NMR. A relatively infamous recent example used pyrolysis GCMS to make low-concentration measurements (hence: nanomolar), which they credulously scaled up by some huge factor, and then made idiotic claims about plastic spoons in brains.

Relatively little quantitative science in this area depends on counting plastic particles in microscopic images, but it’s what gets headlines, because laypeople understand pictures.

[1] as an aside, the choice of terminology here is noteworthy. A simple visual light absorption spectra is also “light based spectroscopy”, but is measuring the aggregate response of a sample of a heterogeneous mixture, and is conventionally converted to molar equivalents via some sort of calibration curve (otherwise you can’t conclude anything). But there could be other approaches that are closer to microscopy, which they also discuss. “Particles per square millimeter” is also a unit of concentration (albeit a shitty one, unless your particles are of uniform mass).

Anyway, the point is that these kinds of quantitative analyses are all trying to do measurements that are fundamentally about concentration, which is why I chose the words that I did.

When you are taking measurements at the detection limit of any molecule that is widespread in the environment, you are going to have a difficult time of distinguishing signal from background. This requires sampling and replication and rigorous application of statistical inference.

> Another thing to consider is that papers generally compare against baseline/control samples,

Right, that’s what a control is.

> and overestimating microplastics in baseline samples may lead to a lower ratio of reported microplastics in the test samples, not higher.

There’s no such thing as “overestimating in baseline samples”, unless you’re just doing a different measurement entirely.

What you’re trying to say is that if there’s a chemical everywhere, the prevalence makes it harder to claim that small measurement differences in the “treatment” arm are significant. This is a feature, not a bug.

We’ve reached the absurd point where all sides of the political spectrum have sacred cows, and an exceedingly poor understanding of scientific reasoning, and all sides also try to dunk on the others by claiming scientific authority.

Comments URL: https://news.ycombinator.com/item?id=47440515

Points: 29

# Comments: 2

No, "we" are not doing that. You are asserting this, and I am saying that you are confusing the completely historically normal function of a newspaper editorial staff with "propaganda". Newspaper owners have, since newspapers have existed, controlled the editorial slants of their papers.

The New York Times does similar things regularly -- but on the left -- and James Bennet famously was pushed out from the Times in 2020 for having the temerity to publish an editorial from a sitting US Senator, because that Senator said something right-wing, and AG Sulzberger (chairman of the Times) demanded his resignation for it.

https://www.politico.com/news/magazine/2023/12/14/james-benn...

> You called the Washington Post opinions section propaganda in another post.

I did not.

> It seems like we all agree about Jeff Bezos turning the options section into his own personal propaganda outlet

No.