Aspergillus niger is a common fungus which causes a disease called black mold on fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food. It is found in soil and indoor environments, where its black colonies can be confused with those of Stachybotrys. Some A. niger strains produce potent mycotoxins called ochratoxins. A. niger spores have wide ranging applications in the fermentation industry and in wastewater treatment. They may pose health hazard if inhaled by people with compromised immunity. Enhanced SEM. Image width: 21.4 micrometers. Magnification: 4673x if the image is printed 10 cm wide.