Aspergillus can produce many mycotoxins - there is a complete list on the website here.
Generally mycotoxins are not usually produced while the fungus is growing well, but once it starts to run out of food or moisture it can happen, sometimes with disastrous effects - see the news article below
Cattle Feeding: What Are Mycotoxins?
Certain species of fungi (molds) produce toxic substances called mycotoxins. These fungi may be found growing on feed, silage, or hay in the field or in storage. Most mycotoxin production occurs in the field before harvest, but poor storage practices can increase already existing mycotoxin levels. Mycotoxins can cause cattle health and productivity problems at very low dosages, parts per million (ppm) or parts per billion (ppb). Mycotoxins are not necessarily produced whenever feed or forage becomes moldy, but evidence of mold indicates a risk of toxins. Fungi growth may also be present but undetectable upon casual observation.
Hundreds of mycotoxins have been identified. Mycotoxins of greatest importance worldwide include aflatoxins, trichothecenes, fumonisins, zearalenone, ochratoxin A and ergot alkaloids. Mycotoxins are regulated by Food and Drug Administration (FDA). The FDA Center for Veterinary Medicine focuses on 5 major mycotoxins in the U.S.: aflatoxins, fumonisins, vomitoxin, ochratoxin A, and zearalenone.
Toxin producing fungi include molds from the Aspergillus, Fusarium, and Penicillium genera. Mississippi weather can be conducive to growth of molds in feedstuffs that are of concern for use in beef cattle diets. Generally, cool, wet conditions favor Fusarium species growth, while hot, dry conditions favor Aspergillus species growth.
Source: Mississippi State University Ag Extension
By far the most frequent potential problems for humans occur in stored foodstuffs such as grain and nuts, so strict storage and testing of imported food is undertaken worldwide.
There is some suggestion in the media that mycotoxins might be part of 'Sick Building Syndrome' and this was covered in the recent AAA meeting. We have complete abstracts and posters from that meeting here