So in wildlands with undisturbed soil profiles- we have Soil cryptobiotic crusts.
https://www.fs.fed.us/rm/pubs_other/rmrs_2014_warren_s002.pdf
These are ecologically tremendously important mix of organisms who occupy the upper few millimeters of soil (soil is a living thing). This ecosystem is destroyed thru plowing or bulldozing soil. Humans kill soil and turn it to dirt.
Dirt does not typically have crusts, but may have spores or propagules from the soil crusts.
Mold is a type of fungi, and fungi are part of these crusts. Cyanobacteria are also very important.
These crusts are most apparent in winter when hydrated...you can SEE the dark blue green soil algae (now cyanob)...in between other cool organisms including mosses, lichen, etc.
But a mold growing in soil crusts is not likely to be the species of mold growing in your drain pipe.
So assumptions that 100% of anything called mold is making some sensitive folks sicker-I merely wonder about that..what exactly in mold IS it...would be certainly an interesting question to answer.