Skip Navigation

9/3/2012 - 9/9/2012

Aflatoxin: Handling Corn

By Charles Hurburgh, Department of Ag and Biosystems Engineering

Corn with known levels of aflatoxin must be directed toward the appropriate feed use, with documentation to the seller of its condition. Normally, aflatoxin corn cannot be blended for the purpose of diluting the aflatoxin concentration. However, in high incidence years, FDA has generally granted a waiver to allow blending for use in livestock feed, using prescribed blending and testing procedures, and with documentation to accompany the blended grain. Iowa has asked for this waiver in 2012; FDA response is forthcoming. Under no circumstances should corn known to contain more than 20 ppb aflatoxin be offered for sale to the general market where the final use is not known at the time of sale. All U.S. export corn is tested for aflatoxin at the port, before it can be loaded on a vessel. By contract, most U.S. export DDGS and gluten feed/meal is also tested. Corn co-products are particularly sensitive because the aflatoxin is concentrated 3 to 1 from the levels of the source corn. In all cases, the very high potential error generated by any aflatoxin analysis should be considered.

The overall incidence of aflatoxin will determine the degree of testing and special handling that will be needed. If the incidence is scattered, relatively infrequent and generally at a low level (most affected samples less than 50 ppb), the normal mixing and handling at elevators will likely hold averages below 20 ppb. However, there are markets that have lower threshholds than 20 ppb (corn wet milling, ethanol plants that export DDGS, feed mills serving dairy); those markets, and their corn suppliers, may test or screen more intensively. Processors typically do not have separate storage or blending capability; these markets are more likely to reject corn based on the aflatoxin concentration.

If the incidence is more frequent and/or the levels of affected lots are higher, load by load screening should be done. The black light test is the quickest but only gives a yes or no result, with some degree of error. Test kits will cause delays in unloading as trucks wait for results before dumping. Either method will give segregation of okay and high, with the high being directed to the appropriate animal feed. If high aflatoxin corn is accepted against a warehouse receipt, the aflatoxin status will be noted on the receipt.

The most severe situation, not likely in Iowa this year, would be a high frequency of aflatoxin loads, and some values very far above 20 ppb (in the high 100s or 1000s ppb). That would mean a quantitative (test kit) result on every load with fairly complex segregation to maximize the use among livestock.



Testing every load, even with the black light method, is time consuming. Another approach is to collect a composite sample composed of portions from a series of loads or lots. For sampling into or out of a storage bin, take a random cut through the flowing stream to get at least a pound of corn from each load. Mix and divide to about 10 lbs for submission to the lab. For monitoring loads coming to a receiving point, such as an elevator or processing plant, put a portion of the sample normally taken for quality testing into a bucket, then mix and divide if needed to obtain 10 lbs for submission to the lab. The portion used for moisture testing will normally provide ½  -1 lb per load.

The composite method will estimate average levels of toxins and of other quality measures if desired.  It will not identify the highest levels or the variation of levels.  With accurate recordkeeping, possible contributors can be identified if a composite shows an unexpected value.


Charles Hurburgh is a professor in the Department of Ag and Biosystems Engineering. He can be reached at 515-294-8629 or e-mail

Aflatoxin: Testing Corn

By Charles Hurburgh, Department of Ag and Biosystems Engineering

Early harvest reports are confirming that there is some incidence of aflatoxin in 2012 corn. The highest potential is in the areas of extreme drought and in cases where August storms put corn on the ground. Three earlier ICM News articles have described the biology and the impact of aflatoxin on the grain market.

  1. Aflatoxin Detected in Fields in Central and Southern Iowa
  2. Crop Quality Issues from the Drought of 2012
  3. Aspergillus Ear Rot and Aflatoxin Production

The most sensitive corn users will be dairy, pet food, direct human consumption (snack foods, etc.) and processors that either export or sell some products to sensitive uses. Ethanol plants and corn wet mills concentrate the toxin in their protein co-product streams. Many ethanol plants export distillers grains (DDGS)  as well as sell to local feed markets.


Testing for aflatoxin

Testing for aflatoxin is very challenging  because of very high sampling error. Individual kernels can contain up to 400,000 parts per billion (ppb). With the typical weight of a kernel, one very high kernel in a 5-pound sample will cause the sample to be about 52 ppb. This individual kernel effect is why large samples and grinding of entire samples is necessary to get useful results. If the sample with the very high kernel were divided as whole corn to get 1/20 for the actual analysis, there would be 19 possible divisions with none and one that would test over 1000 ppb!  The more grain is moved and mixed the more homogenous the aflatoxin will become. Samples taken farther down the grain distribution chain are, in general,  more accurate, but action to control problems is more complicated after the first point of delivery.

Samples should not be divided as whole kernels to reach the smaller size needed for testing. A minimum of 5 pounds is required to have statistical validity; even then the sampling error for aflatoxin testing is 25-40 percent.

Most testing for aflatoxin in market channels is done with immunoassay test kits. An antibody binds with toxin that has been extracted with a solvent from a small ground sample. The antibody is also attached to a molecule that glows (fluoresces); if the flourescence is read optically, then a quantitative (actual ppb) value can be determined. If the color change is just visual at a certain level, then a qualitative (yes or no) value above the preset threshold of the kit is determined.  The USDA GIPSA has evaluated and approved test kits for various toxins. See this link for a current list of approved kits.

Test kits take 5-10 minutes per sample at a cost of about $10-15, including labor time. In high throughput operations, testing every inbound load would require additional personnel in the grading area, and will cause 10-15 minute delays for each truck before unloading.

Many buyers prefer to use off-site labs for testing; this is also true for crop insurance settlements where the adjuster has taken a sample on which to base the settlement.  A list of labs in Iowa is available on the Iowa Grain Quality Initiative website. USDA-GIPSA grading agencies, as well as several private labs and the Iowa State University Veterinary Diagnostic lab, can do toxin testing on submitted samples. 

Scanning with a black light (366nm) has been used to identify samples that potentially contain aflatoxin. Kojic acid, also formed by actively growing Aspergillus flavus, will fluoresce blue-green-yellow under the black light. A tinopal color standard (Seedburo, Inc, Chicago, IL) is strongly suggested to provide the comparison for fluorescence in the corn, because many compounds will fluoresce other colors under the black light. Historically, the black light gives about 30 percent combined false positives (glow but not aflatoxin >20ppb) and false negatives (no glow but aflatoxin >20 ppb).  However, in the 1983 and 1988 outbreaks, we found that when 5-pound samples were scanned, samples with one or more glowing particles per pound (five in a 5-pound sample) had a much higher chance of aflatoxin over 20 ppb than those with less than 1 particle per pound. The average aflatoxin of those with glowing particles but fewer than one per pound was 6 and 10 ppb for the two years respectively.  A more complete protocol for using the black light as an initial screening method is posted at


Charles Hurburgh is a professor in the Department of Ag and Biosystems Engineering. He can be reached at 515-294-8629 or e-mail

Aflatoxin: Crop Insurance

By Charles Hurburgh, Department of Ag and Biosystems Engineering, and Chad Hart, Department of Economics

Aflatoxin is covered under multi-peril crop insurance. The settlement is done as a deducted percentage of actual yield depending on the aflatoxin level. Producers will receive the grain after settlement. 

If a claim is made, the aflatoxin level will be determined in the field, before the grain is harvested and  put in storage. An adjuster will either hand harvest ears from predetermined representative locations in the field or collect samples at harvest from trucks/wagons. Strips may be left for later harvest or hand sampling, at the direction of the adjuster. Hot weather conditions can cause the levels in strips to increase beyond harvest levels. An elevator or processor can also be approved to collect and combine samples for submission to a lab, if the corn is marketed from the field. Testing must be done by lab approved by the insurance carrier, generally a disinterested third party capable of accurate mycotoxin testing. A list of labs, including the USDA-GIPSA agencies serving Iowa, is at The Risk Management Agency has posted a fact sheet on aflatoxin testing for insurance purposes. Aflatoxin levels must be above 20 parts per billion before insurance payments are impacted.

Elevators and processors typically are not approved to do crop insurance testing for aflatoxin. Complete USDA-RMA loss adjustment procedures are available. This includes sections on the adjustment of aflatoxin losses. Speak with your insurance carrier for specific instructions.

The important points are 1) that crop insurance must be called before harvest; no settlements will be made for corn already in storage ; 2) that producers getting a settlement for aflatoxin must direct the corn to an approved use for the level present, with documentation of test results and 3) that all measurements, samples, and testing must be done under the supervision of the adjuster.  Aflatoxin is an adulterant under Food and Drug Law, with specific provisions on how it should be handled, depending on determined level.


Charles Hurburgh is a professor in the Department of Ag and Biosystems Engineering. He can be reached at 515-294-8629 or e-mail Chad Hart is a grain marketing economist in the Department of Economics. He can be reached at 515-294-9911 or

This article was published originally on 9/10/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.