This post is an update of my suggestion from before, which I think would work well with the mk3 update germ system
This suggestion would add a new "germ" to the game called Dust.
Dust would be produced by machinery, breaking blocks, and living things(way slower over time)
As with most of the other germs dust will not cause significant harm but It would make it harder to breath, more so than other germs, to the point where your dupes could start taking small amounts of damage.
I'm not sure how hard this would be to do in game, if there is another way to handle it let me know; Dust would not grow in the sense like other germs but rather It would be produced in set amounts by its producers and wont go away on its own. It would also try to settle on the bottom of your base.
Dust would be eliminated by touching water in which case It would turn into mud(new liquid), with steam it would produce polluted dirt. With mud your dupes would be slowed down when walking through it and have a chance to slip(causing a sprain debuff slowing your dupe down for a little bit) . mud would also inflict a muddy status effect that would cause a moral penalty until your dupe takes a shower.
Mud can also be evaporated into polluted dirt and steam.
If anyone has any suggestions to add to this idea I would love to hear!
Edit one: Animals could make "mud" occasionally.
Edit two: Gain a little bit of immunity based on the mining level.