[kragen]

But the claim in question is one of the best-known and most thoroughly established claims in all of toxicology. Asking for scientific research supporting the biocompatibility of PTFE is akin to asking for scientific research supporting biological evolution or the claim that people have landed on the moon: it's a sure sign that the person making the demand has a pre-existing flimsy pretext for rejecting literally all the research in the relevant field, which did indeed turn out to be the case; see https://news.ycombinator.com/item?id=32517203.

[blix]

If it's truly such a well established claim it should be trivial to find and link a study actually demonstrating its safety when ingesting small amounts over a large period of time. No such study was linked. Probably because longitudinal studies are extremely rare.

It's not a rejection of all research to say that some questions remain unanswered. In fact, I'd say it is the foundation of good science to understand which claims are supported by evidence, and which claims are not.

[kragen]

There are half a dozen studies per year, going back decades, assessing the safety of PTFE in implants. Many of them are longitudinal. Chemists routinely boil PTFE in acids such as hydrochloric and sulfuric for hours without degrading it even slightly; such degradation would contaminate their reactions.

I bet you can't find a study demonstrating natural selection in the split-leaf philodendron, either, but that isn't a good reason to go around saying "some questions remain unanswered" about whether the split-leaf philodendron is an exception to the laws of evolution.

[blix]

The two comment threads are the same discussion so I'm merging my responses.

> I bet you can't find a study demonstrating natural selection in the split-leaf philodendron, either, but that isn't a good reason to go around saying "some questions remain unanswered"

It absolutely is! The criterion for whether a question has been answered is whether that question has actually been asked, studied, and answered. In cases where there is no specific evidence, you attempt to make assumptions that extend existing evidence into spaces that it does not explicitly cover. But these aren't answers; they are educated guesses. Some guesses are better than others, and really the fundemental act of science is feeling out these hypotheses and deciding which ones are sturdy and which are shaky.

So for example consider the claim 'PTFE doesn't affect human health when ingested, because there is strong evidence that is safe in implants and is chemically inert in acids.' This claim relies on two assumptions in the absence of quality direct supporting evidence: (1) Safety in one biological context directly transfers to other biological contexts and (2) Chemically inert compounds cannot affect human health. There is mounting evidence against ~both~ of these assumptions, and so claims based on them should be treated with caution, and probably as warranting further study. This is no witch-hunt, this is simply using critical thinking and available evidence to gauge the validity of assumptions, and updating the validity of claims based on changes in the validity of underlying assumptions. This process ~is~ the scientific method.

> Nanometer-sized pores matter enormously, (...) but not in ways that make other forms of amorphous silica more toxic than silica gel.

Try replacing your morning cheerios with silica gel and let me know the results. The pores in silica gel are specifically interesting because they allow silica to readily form hydrates. The human body has a lot of water in it. There are absolutely health effects that depend on the physical shape of silica in addition to its chemistry compared to say, consuming an equal mass of fully dense quartz particles.

You'd probably have to eat a lot of silica gel to really feel the effects, but there are other more accessible and serious health concerns that are driven by nanometer or smaller physical effects. The reaction between diet coke and mentos is primarily physical, driven by nanometer-scale surface roughness on the candy. Proteins sometimes fold in abnormal shapes, and in the right circumstances, the presence of a chemically identical but differently-shaped protein can induce other proteins to change shape as well, leading to prion diseases such as Mad Cow and CJD, both of which can be acquired via ingestion of the trigger protein shapes.

The claim that nanometer-sized structural changes in a compound can have no effect on human health when ingested is demonstrably false. Obviously, this calls directly into question the dependent claim that chemically inert compounds can have no possible impact on human health when ingested.

[kragen]

Yes, you can dehydrate your tissues by eating dehydrated silica gel. But when hydrated it's a Generally Recognized As Safe food additive in quantities up to 3% (5% in the EU). You can probably eat a lot more than that but it will grind up your teeth. (By the same token, someone could strangle you with a PTFE cord, a fact that has no bearing on its toxicity.)

Quartz is not amorphous silica, and unlike amorphous silica, it's carcinogenic if you inhale it.

You don't get nanometer-sized structural changes in teflon by scraping it off your skillet with a spatula. You're being ridiculous.

I'm interested to hear what response you get from biologists when you propose to them that natural selection might be inoperative in the split-leaf philodendron. I imagine they'll wish they had a PTFE cord handy.

[blix]

> Quartz is not amorphous silica, and unlike amorphous silica, it's carcinogenic if you inhale it.

Crystalline silica is still silica.

> You don't get nanometer-sized structural changes in teflon by scraping it off your skillet with a spatula. You're being ridiculous.

The words of someone who has not spent time analyzing electron microscopy of fracture surfaces :) It absolutely does without any possible shred of doubt. But that's not even the point; the point is that the fine physical structure of compounds can matter in biological systems. If you accept this, that it is plainly obvious that chemical inertness of a compounds is an obviously insufficent condition for safety.

> I'm interested to hear what response you get from biologists when you propose to them that natural selection might be inoperative in the split-leaf philodendron. I imagine they'll wish they had a PTFE cord handy.

If you spend a lot of time around people with science PhDs, you will quickly learn that most of us are keenly aware of how little we actually know and how much of it is guessing. Murdering people over disagreements is the domain of religions, not science. Sadly for many these two are interchangable.

[kragen]

Conceded. I guess I was wrong. Too bad I was so arrogant about it!