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).