What toxic substance might be present in moldy corn at harvest?

Aflatoxin is a toxic substance that can be produced by certain types of mold, particularly Aspergillus species, which often develops in corn that has been damaged or improperly stored. When corn is harvested in conditions that promote mold growth, such as high moisture levels or physical damage, aflatoxin can accumulate and pose a serious health risk to both livestock and humans who consume the contaminated corn. It is a potent carcinogen and can lead to various health issues, making it a significant concern in agricultural practice and food safety.

While other substances like nitrates, Salmonella, and E. coli can also be associated with crops, they arise from different environmental conditions or contamination sources rather than from the mold growth itself present in moldy corn. Nitrates are typically linked to high fertilization rates and certain environmental factors, while Salmonella and E. coli are more associated with bacterial contamination rather than mold. Hence, aflatoxin is specifically noted for its presence in moldy corn, making it the most relevant answer for this question.