The creatures on this world tend to favour arsenic as a replacement for phosphorous in their biology. There's an overabundance of it in the ground soil, and very little phosphorus.

The equivalent of mushrooms on this world pack their spores with arsenic as an essential chemical nutrient for their spawns survival.

field of mushrooms with a dark brown cloud of spoors rolling off like smoke

Is it possible that the resultant arsenic spore cloud would be dense enough to cause arsenic poisoning to anyone who breaths it in, over an appreciable amount of time, say a couple of hours? Assume that unlike the above gif, the spores become well mixed in the air (this may or may not impact how much arsenic they can contain), and the cloud rises to at least a few metres. More like the mist seen here

Mushroom spores are, from some googling, about 40 micrograms in weight, and the LD50 of 13 mg/kg. Some mushroom spores contain phosphorous at levels of 10-20 g/kg, so the arsenic in a single spore was a 1-to-1 replacement, each spore would contain 0.8 micrograms.

At those levels you'd need 16,250 spores per KG of person to get an LD50. A human of 80kg would need 1.3 million spores, and "a single basidiomycete mushroom is capable of releasing over 1 billion spores per day". That means in an hour something like 41 million spores per hour if it was released evenly throughout the day. It feels like this is more than enough spores.

However I don't know if my substitution of arsenic for phosphorous makes much sense, nor how dense the cloud of spores (spores per volume of air) would be?

Is this arsenic spore cloud something that could reasonable be lethal?

Please note: this question is tagged

This tag should clue in any potential answerers based on it's tag wiki: "Asks if a given concept is realistic in a given context. Answers should say yes or no, with supporting info. " (emphasis mine). As such I am not soliciting discussion or suggestions on ways to improve this concept. The context above should be taken as an inviolable fact, and not something to be iterated on as part of this question.


2 Answers 2



Firstly, as far as I can tell, the substitution of makes sense. Although it is unlikely that all the phosphorus would be replaced by arsenic and your fungus will still much prefer phosphorus to arsenic, given that (it seems like) the idea of arsenic based life on Earth was seriously considered in the scientific community, it is definitely plausible. The only problem with your substitution that I can find is that because arsenic has a higher atomic weight than phosphorus, there would actually be about 2 micrograms per spore, so only around 7,000 spores per kilogram are required to reach the LD50.

Under ideal conditions, say 0.1m/s wind (I have to assume some wind or I cannot find a mechanism for the spores to get off the ground), if your patch is roughly a square with side length 2 meters (as in the gif), the spores will spend around 10 seconds in the patch. If that patch has 1000 mushrooms (this seems reasonable to me given the density of mushrooms in the gif) and each mushroom produces a billion spores a day, at any given instant, there will be around 10 million spores the patch.

If the updrafts are perfect (I am still assuming ideal conditions), the spores might be vertically spread out uniformly over the 2m or so of our theoretical person's height. If the person breaths in 7ml of air per kilogram per breath, they would need to inhale 700 times before they get the LD50. This would take around 45 minutes, but given a larger patch (that takes longer for the person to cross and has a higher density of spores), the arsenic could make it impassable. Given a 1m/s walking speed, and no holding of breath while walking on the patch, the patch would need to be 70 meters wide to give the LD50 to someone walking through it. Of course, the person would encounter a bit of arsenic while approaching the patch, so this width could be even smaller with a favorable wind direction. Also, even if it is not necessarily fatal, breathing while in a smaller patch could cause a lot of nasty symptoms that could last for months.

  • $\begingroup$ This is a great answer. Thank for shoring up my calculations and finishing it off with more information! $\endgroup$ Commented Jul 2, 2021 at 22:52

It would be a rough world for earth humans, spores or no.

Concentrated arsenic spores would be very bad for humans. edit: Could they be lethal for earth humans: YES. Windblown dust from arsenic-laden soil would also be bad for humans over a longer period. The whole world would be poisonous for earth humans. Just inhabiting this world will pretty much guarantee arsenic poisoning eventually.

But probably not for the natives. edit: Could arsenic spores be lethal to creatures adapted to this high arsenic world: PROBABLY NO. If the high arsenic soil is how this world is everywhere, life native to this world would probably be adapted to high arsenic levels (even if not to the degree that these fungi are) and so arsenic spores would not be as hazardous as they would be to creatures from our world.

This might be a good world for earth humans with syphilis. Maybe there could be a spa where syphilitic folks come for a time to soak in warm springs, huff some arsenic spores, participate in drum circles, write inspirational poetry. That sounds good.

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    $\begingroup$ Thank you for answering, however this is a [reality-check] question: "Answers should say yes or no, with supporting info." As it stands I don't see your supporting information, this is more of a large comment as it stands? $\endgroup$ Commented Jul 3, 2021 at 17:11
  • $\begingroup$ @Pureferret - I thought my first sentence "would be very bad for humans" would be interpreted to mean "yes". I will add "Yes" to be clear. I thought is was important to make a distinction between poisonous for earth humans and poisonous for natives of that world. I do not think I can make that any clearer than the second paragraph dose. $\endgroup$
    – Willk
    Commented Jul 3, 2021 at 18:14
  • $\begingroup$ It was more the support for that conclusion I felt was lacking. Have you see the (currently only) other answer? $\endgroup$ Commented Jul 3, 2021 at 18:34

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