Mycotoxins are poisonous substances produced by certain molds found primarily in grain and nut crops, but are also known to be on celery, grape juice, apples, and other produce.

There are many mycotoxins and scientists are continually discovering new ones. The Food and Agriculture Organization (FAO) of the United Nations estimates that 25% of the world's food crops are affected by mycotoxins, of which the most notorious are aflatoxins.

References

USDA Food Safety and Inspection Service. http://www.fsis.usda.gov/Fact_Sheets/Molds_On_Food/index.asp