Aflatoxins in Corn

By Heather Benedict, Agronomist Specialist

One of the big topics in agriculture this harvest has been the presence of aflatoxins in corn.  Aflatoxins are compounds produced by the Aspergillus molds.  While some molds like the Penicillum molds produce beneficial compounds like penicillin, the Aspergillus flavus produces toxic compounds known as aflatoxins.  Although there are several compounds produced by this mold, the most toxic is the B1 compound.

The aflatoxins produced by the Aspergillus mold are toxic to humans and livestock.  These compounds are carcinogenic, or cancer causing.  In humans, as little as 20 parts per billion (ppb) can be carcinogenic.  In livestock, the toxins can affect their liver and their ability to grow and thrive.  Because of the effects of these compounds their presence in the corn is carefully regulated by the USDA.  The corn used for human consumption is scrutinized closely for the aflatoxins, and the corn used for livestock is also carefully regulated.

Although the corn grain contaminated by the aflatoxins can be used for ethanol production the toxins remain in the by-products.  In fact, the levels of the toxins are concentrated in the by-products.  Ethanol processing facilities often do not take corn contaminated by the toxins because they will then be unable to sell the dry distiller grain by-products to livestock producers.  If the facilities do accept the corn the price for the grain will reflect the fact the by-products are essentially useless.

The levels of the aflatoxin that are considered toxic to humans and livestock are extremely low.  For humans the level of 20 ppb is toxic.  For livestock, the acceptable limits are determined by the class and size of the animal.  This is because younger animals or breeding animals are more susceptible to the effects than older larger animals. Cattle in feedlots can tolerate as much as 300 ppb of the aflatoxins.  While the acceptable levels of the compounds vary among organisms, the levels are still very low.  An example of one part per billion is one drop of ink in the largest semi tanker truck full of water. 

There are several methods used in testing for aflatoxins.  One of the most common is using a black light on the grain, however, while this method may show the presence of the mold it is not useful in determining the presence or amount of toxin present in the grain.  Other methods of testing are more useful in determining if the molds have produced toxins and how much may be present in the grain.

It is important to determine if there is A. flavus or the aflatoxins present when the grain is harvested.  The Aspergillus molds are greenish yellow to yellowish brown powdery mold growing on or between the corn kernels. The A. flavus can attack the corn in the field.  It is able to invade through the corn silks or in association with insect damage to the ears.  Drought and heat stress are associated with higher levels of infection.  While the molds may be found in the field they are able to grow extremely well when corn is combined in a bin.  The kernels come into contact with each other and can spread the contamination.  Because the temperature in a grain bin is unlikely to drop quickly enough to affect the growth of mold, it is imperative that the moisture levels be lowered quickly for harvested grains.  The optimum moisture is 13% or below.

            Corn growers need to contact their insurance providers to determine the levels of the aflatoxins in their field before harvesting this year.  Many of the insurance companies need to determine the probability of infection before the grain is deposited in a bin or taken to elevators.

            This year we can see that the drought and mild weather during the past winter continues to affect the harvest.  Corn growers need to check for aflatoxins in the grain they harvest.  The stalks and silage should be checked for nitrates before being fed to livestock.  This year it is more important than ever to test both the grain and by-products of corn before using them for feed.