This page of our Control guide contains a walkthrough for a side mission called What a Mess: Even More Mold. You will learn, e.g. where to find the mold.
To start the mission, pick-up the note from the board found in Janitor's Office To receive this mission, you need to complete the previous one, called What a Mess: Clear the Mold.
Walkthrough: We're back for some more mold. Travel to NSC Coolant Pumps in the Maintenance. Clear the area from enemies, and then use levitation to access a higher-level area. You'll find mold here.
The next source is between the columns, near the corridor full of mold on the walls.
Another targeted mold is on the wall not far from a hanging scaffolding.
Another source of mold is above the hanging scaffolding.
Your next target is on the wall, next to a corridor full of mold.
The next source of mold is literally a little further away, on the next wall.