When certain types of fungus grow on food, they produce minute amounts of toxins called mycotoxins. Some of these fungi (primarily Aspergillus flavus) produce the very lethal mycotoxins called aflatoxins. Aflatoxins are remarkably potent, often causing disease even when ingested in minute amounts. Chronic exposure to aflatoxins can damage the liver causing liver cancer.
Peanut is a legume that is notorious for the growth of aflatoxins.
Food Quality Division provides analysis for aflatoxin that includes Aflatoxin B1, Aflatoxin B2, Aflatoxin G1 and Aflatoxin G2.