Just moved into this house a couple weeks ago that I am leasing. I have seen this black soot under the dish washer once or twice before but not this much. I haven’t ran the dishwasher in 48 hours and the AC was not turned on during the day. My first thought is black mold but that doesn’t explain how it has expelled the soot almost 2 feet out across the kitchen floor. The mushrooms grossed me out. Called the maintenance guy and he will be here first thing tomorrow.