Aflatoxin Expert Talks Drought, Corn Blending, 2013 Weather

October 26, 2012 12:00 AM

 While experts initially expressed concern that fungi-produced chemical compounds known as aflatoxins might damage U.S. corn yields thanks to the drought, results appear mixed. 

In September, experts with the University of Illinois reported that some milk had been turned away because of unacceptable aflatoxin levels. Also that month, experts at Purdue University advised farmers to be on the lookout for the mold-like substance, whose presence can vary widely depending on environmental factors and planting time.

But the news hasn’t been all bad. Experts at Michigan State University reported this month via that aflatoxin has been less prevalent than expected.

John Leslie is a distinguished professor who heads the plant pathology department at Kansas State University. In an email interview this week, he explained why aflatoxins can be cause for concern; described its relationship with drought; and shared his thoughts on the USDA’s decision to allow blending of corn containing aflatoxins.

What is aflatoxin, and why is it a concern for corn farmers?

Aflatoxins are a family of structurally related chemical compounds synthesized by a number of species of fungi in the genus Aspergillus, with Aspergillus flavus the fungus usually of greatest interest and aflatoxin B1 usually the most important aflatoxin.

Aflatoxins are toxic to humans and many other animals at sufficiently high levels, although for humans the more common fear is their carcinogenic capabilities and the increase in liver cancer as a result of exposure to them. Long-term chronic exposure to sub-clinical levels of aflatoxins can result in partial suppression of the immune system, rendering those so exposed generally less resistant to other microorganisms to which the individual might be exposed.

Human deaths due to aflatoxins in the U.S. and other developed countries are rare because our food regulatory system usually identifies contaminated materials and restricts their entry into the commercial food and feed chains. There have been outbreaks of aflatoxin poisoning in Africa, most recently Kenya, in which several hundred people have died due to aflatoxin poisoning from eating corn containing too much aflatoxins.

There are currently major multi-national efforts to reduce the level of aflatoxin in both corn and peanuts in Africa to reduce the health problems these compounds can cause there. The most recent aflatoxin problem in the U.S. occurred a few years ago when contaminated dog food killed a number of pets.

Earlier this year, the USDA authorized states such as Iowa, Illinois and Nebraska to blend aflatoxin-affected corn with unaffected corn. Is this normal? How does this decision benefit farmers, and what should consumers know about these blends?

Maximum aflatoxin levels allowed in corn are set in the U.S., with the exact level determined by the end use for which the corn is intended. Aflatoxin can be carried through the milk of an animal that consumes corn contaminated with the toxin. Thus grain intended for dairy cattle feed, for example, is allowed to have much less aflatoxin contamination than is grain intended for beef cattle.

Blending allows the mixing of grain with a lower level of aflatoxin with grain that has higher levels of aflatoxin, i.e. grain exceeding the regulatory limit, so that the final mixture is below the regulatory threshold. USDA usually does not allow the grain to be blended and rejects the contaminated grain to keep it out of the food system.

The blends being allowed this year will still be safe and will meet all of the food regulatory standards. The blends probably will have levels of aflatoxin that are closer to the limits than might be found in other years.

The USDA decision benefits farmers by allowing them to sell a portion of their crop that they might not have been able to sell if it was not blended with grain with a lower level of contamination. For consumers, it means that the average level of aflatoxin in corn will be increased.

On average the grain will all meet the USDA standards. The problem with aflatoxins is that they often are distributed unevenly in the corn lot, with portions of the lot being relatively highly contaminated and other portions not being contaminated at all.

To the extent that the grain samples are not thoroughly mixed, there is a risk that portions of a lot may exceed the limit even though the lot as a whole is perfectly safe. The sampling techniques used to detect aflatoxins in grain samples minimize this problem, but the problem never goes completely away and becomes more important as the average aflatoxin level increases.

To what degree has aflatoxin created problems for farmers this year, compared to what some experts feared? How did the drought affect the level aflatoxin in corn, and what do you expect farmers will find as harvest wraps up?

In general, drought increases the amount of aflatoxin found in corn. A hot, dry year such as this one in which the plants are stressed may have much higher levels of aflatoxin than would be found in a "normal" year.

What can farmers expect next year with regard to aflatoxin?

The fungi that produce aflatoxin are ubiquitous in the field and will not go away, so there is the potential for an aflatoxin outbreak every year. Some corn hybrids are less susceptible to aflatoxin contamination than are others, but aflatoxin susceptibility should be only one of the factors that a farmer considers when deciding which hybrid is the best for them to plant.

The weather is the most important factor in determining whether aflatoxin contamination will be a problem. Hot, dry weather is associated with increased aflatoxin production by the fungus. If the predictions of various climate models are correct and the central portion of the U.S. will experience more hotter, drier summers, then the size of the aflatoxin contamination problem is likely to increase.

However, every year is a different event, and the amount of aflatoxin contamination will depend on that particular year's weather and not on broader changes alone.

What other comments would you like to make?

Farmers who are particularly sensitive to aflatoxin contamination as a problem might consider an alternative crop, e.g. grain sorghum, which is much less prone to aflatoxin contamination than is corn but which produces a grain that often can be substituted for corn in feeds and other products.

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