Aflatoxin and other mycotoxins, primarily from aspergillus mold, are a big concern with raw wheat flour and corn products. Rodent excreta is not difficult to sieve out. Wheat and corn for human consumption is usually randomly sampled and tested for mycotoxins but nothing requires this, though most grain sale contracts specify testing and thresholds.

Mycotoxins can cause severe illness (usually not lethal though) and are not deactivated by normal cooking temperatures.