Black sand/ iron sand

I am interested to know peoples' experiences with black sand used with axolotls.
I recently joined a local (NZ) Facebook group for axolotl keepers. The topic of substrate came up, and I mentioned black sand, at which point a very vocal member immediately jumped down my throat (New Zealand internet groups are really big on the whole "shaming people publicly" thing, which is why I generally stick to International groups rather than local NZ groups - they tend to more civil)
Without going into the nastiness of the replies, the member (actually the moderator) seemed to have an unshakable belief that iron sand causes liver failure in axolotls.
While I know that excess dietary iron (especially from supplements) in mammals can cause liver failure, I can find no evidence that iron sand causes liver failure in axolotls. NZ iron sand is a hematite sand, and as far as I am aware, the iron is bound, and therefore inert.
Her response was that "everyone who uses black sand has liver failure in their axolotls", although she was unable to give any specific examples, and didn't seem to personally know of any instances.
As far as I can find, some people who use black sand experience liver failure with their axolotls, but many people who use black sand don't. Some who DON'T use black sand experience liver failure with their axolotls. I tend to think that it is not the black sand that is the issue.
Also, if so many people were having liver issues with their axolotls in conjunction with using black sand, I expect many of them would be (metaphorically) jumping up and down and screaming about it, which would invariably lead to a lot of internet posts on the issue, yet I have not been able to find ANY post on the issue.
Does anyone have any actual evidence or experience with this issue?
What is the experience of people who have used black sand?
Thanks :happy:

Hello urbanfrog I’m sorry to hear about your experience, these people are in a position to advise but use it negatively to massage their egos. Ignorant self opinionated people who drive others away from our hobby. I know these remarks are hurtful as I’ve had them too which resulted in me leaving two Facebook Salamandra groups. I’ve considetsble experience and an extensive collection.This place seems ok although I’ve seen some over inflated egos here too so I don’t contribute much these days.
factual statements need citing with a credible author. Liver damage? Are there lab tests? I keep my axolotls on black sand as I like the contrast. It’s volcanic and rinsed free of any soluble chemicals etc but I know there are dyed sands available. I believe this sand originated from beaches rather than a by product from industry. It is fine like silver sand. I don’t use it deeper than 1cm as I’d be concerned with pockets of anaerobic bacteria. I’ve used this sand in my show tank for twenty years or more. Breeding and rearing tanks don’t have a substrate which makes them easy to syphon off muck each day.
I’ve not used iron based sands because they’re not available but I have read nothing to suggest they are harmful. Mind you, I've seen streams polluted by iron run off (reddish deposits and discolouration) and not much lives in that. As you point out, the iron is bonded and unlikely to enter the water of your aquarium and in any case, water changes would dilute this. I’m sure a Google scholar search would find credible information.
This mentions iron toxicity.
http://www.jstor.org/stable/1443954?seq=1#page_scan_tab_contents
You keep researching and enjoying your animals and sharing ideas and don’t be put off by these people.