Mars city question

[Vitto]

While completely isolated self sustaining ecosystems may currently be beyond our grasp, it doesn't mean we can't come close

But would a colony on Mars be really a closed enviroment? If it is just a scientific mission for "plant the flag" or a demostrator for a Earth-Mars transport then I guess it could be completely close, relatively speaking.
Instead, if we are talking of a true colony, with the goal to grow and expand, I guess you should have in place all the tech to extract (at least) CHNO from the enviroment and replenish any shortage in your base.
I admit that refining trace elments to produce things like processors or sensor could be a problem without a refinery.

Toxic molds have been detected on both Mir and the ISS, for example, although in very small concentrations so far.

In the worst case scenario I guess you could flush the atmosphere and freeze/dehydrate to death the bastard.

But getting a Mars base to the point where it can grow its own food (at least in principle), source its water from the planet, and produce its own air should be doable with tech that is less advanced than what a full on 'Biosphere Mars' would require.

If you work with aeroponics, if we'll use that to grow food and not something more pratical like a in-vitro system, you can probably remove almost any toxin with a good membrane in your working fluid.
Solid wastes can be incinerated so you should be good with that too unless your toxins are atomic in nature (e.g.: arsenicum).

It's also possible to separate toxins (so they can be safely stored) using biological mechanisms; it might not even be necessary to do any bioengineering to achieve that. A good example is milk vetch, which is very good at extracting selenium from the soil.

Assorted toxins can be removed by bioremediation:

Bioremediation - Wikipedia

Frontiers | Potential Biotechnological Strategies for the Cleanup of Heavy Metals and Metalloids | Plant Science (frontiersin.org)

Got a biotech degree so I know the argument discretly well. A problem with bioremediation is that is NOT intensive, at least using the classical microrganism or plants/algae, so IMHO it's really not viable in a compact base where space is scarce. Dedicating plants to remove toxins from your effluent is a real waste if you're not to eating them, again IMHO.

Still, it is indeed dirty cheap for what it does: removing heavy metals from a soil in an industrial setting would be an expensive pain in the ass. Collecting plants, burning them and vitrifing their ashes is much better from the point of view of the bottom line
 
Anyway, using biobased products to do the job is entirely possible if you use purified enzymes so you can get an increase in volumetric productivity of a few order of magnitueds.

I presume that an advanced purification plant could remove any molecular toxin without any problem so the deal is with the toxic elements: you could remove those using affinity ligands (reusable), or turn them into insoluble compounds, or filter them through an appropiate membrane. Not necessary with a biotech method.

One of the sets of problems for initial colonization will be to provide all the on-site support needed to solve potential problems which would be fatal if they have to wait for solutions that could be six months or more away.

After the fact, of course, many people will complain about all the “waste” of sending equipment and consumables that were never needed.

You would be mad to start colonization without one or more rescue package in close orbit ready to deploy in case of trouble. If you need something critical from Earth you're screwed the time it get there...