[jandrewrogers]

> Arsenic at 0.0025 mg/L

That is well below the noise floor. Like the similarly toxic selenium, arsenic is an essential micronutrient in animal biology. It is possible to be deficient in arsenic, though rare in practice. Natural background levels are far higher in many locales with no adverse effects.

I often see trace quantities of arsenic trotted out by the popular media for scaremongering purposes. Examples like the above are an immediate red flag.

[nradov]

Could you expand on what makes arsenic an essential micronutrient? What are the clinical signs and symptoms of severe arsenic deficiency? I've never heard of this before.

[jandrewrogers]

IIRC, severe deficiency of arsenic leads to a type of wasting. The precise role is uncertain. Based on animal models the rough estimates for human requirements are similar to selenium.

Humans get enough arsenic from water and other background sources that deficiency is virtually unknown. My understanding is that there was historical anecdotal evidence for rare arsenic deficiency from animal husbandry that caused it to be investigated.

These days they systematically test for the trace micronutrient status of e.g. heavy metals by inducing extreme deficiency using mammal models. Most of the time nothing happens but it is difficult to eliminate the possibility of contamination creating a null signal.

Probably the most surprising element for which they have suggestive evidence of biological necessity is lead.

[nradov]

Could you give us some specific citations for evidence of biological necessity for arsenic and lead? I searched on PubMed but couldn't find anything.

[jandrewrogers]

It is damn near impossible to search on Google for this literature today. Fortunately, some of the links have been posted to this site before, which is searchable. :)

Here is the first good reference I could find, which surveys some of the other literature. It mentions lead in rat models.

https://pmc.ncbi.nlm.nih.gov/articles/PMC2246629/

[pegasus]

Since maybe half a year ago, the best way to search stuff like that, by a huge margin, are frontier models like ChatGPT or Gemini. Here's what they found, the TLDR is that lead is much less likely to be essential (in extremely minute amounts) than arsenic, which has been proven to be beneficial in trace amounts for a bunch of mammals. Since those experiments cannot be done on humans, we don't know if it is the same situation in our case, but the null hypothesis at this point is that it is.

https://chatgpt.com/share/6a0d522f-5688-83eb-b80c-0f7b157fae... https://gemini.google.com/share/e2e52489a41e

[jandrewrogers]

That is an accurate summary of the literature as I remember it. Arsenic has been replicated in a bunch of animals including non-mammals. It seems to generalize well and the background is substantive. There are also plausible hypotheses for mechanisms of action. The assumption is that a common effect across a sufficiently diverse set of animals applies to humans, which is probably a good heuristic.

The evidence for lead is much more sparse. It is interesting, and plausible, but without more evidence it is more of a curiosity. For better or worse, there has been zero interest in investigating that anomaly further. People should avoid lead exposure regardless.

Thankfully elements like mercury never show up in these studies. Nothing in my chemistry training suggests that mercury by nature could ever be anything but toxic to life and the evidence seems to support that. It would be weird to find out that was wrong, though I would accept it with sufficient evidence.

[lazide]

It has no known physiological role in humans. Selenium has similar stuff going on. [https://en.wikipedia.org/wiki/Arsenic_biochemistry]

[selectodude]

It’s not hard to figure this stuff out yourself.

[AnimalMuppet]

Perhaps not. At the same time, when a person makes a claim, and several (or several hundred) people read it, it seems more efficient to ask the person who made the claim to supply the documentation, rather than making the several (hundred) people all do the looking. The looking does not have to be hard for this to be true.

Also, just in general debate terms, the one who makes a claim is the one who has the burden of substantiating it.

[nradov]

It is hard. I did some searches before commenting and couldn't find anything about arsenic deficiency. I don't know much about arsenic biochemistry so could you kindly point us to a good source?

[pegasus]

It's super easy with ChatGPT, for example. See my other reply in this thread, I've included the responses there.