E. Mycotoxins
Mycotoxins are toxic compounds produced by fungi that occur naturally in grains. When consumed at elevated levels, mycotoxins may cause sickness in humans and animals. While several mycotoxins have been found in corn grain, aflatoxins and deoxynivalenol (DON or vomitoxin) are considered to be two of the important mycotoxins.
The U.S. grain merchandising industry implements strict safeguards for handling and marketing any elevated levels of mycotoxins. All stakeholders in the corn value chain – seed companies, corn growers, grain marketers and handlers as well as U.S. corn export customers – are interested in understanding how mycotoxin infection is influenced by growing conditions and the subsequent storage, drying, handling and transport of the grain as it moves through the U.S. corn export system.
To assess the effect of these conditions on aflatoxins and DON development, this report summarizes the results from official USDA Federal Grain Inspection Service (FGIS) aflatoxin tests and from independent DON tests for all the export samples collected as part of this survey. Details on the testing methodology employed in this study for the mycotoxins are in the “Testing Analysis Methods” section.
1. Aflatoxins Testing Results
FGIS tested 412 export samples for aflatoxins for the Export Cargo Report 2013/14. Results of the 2013/14 survey are as follows:
- 381 samples or 92.5% of the 412 samples tested had no detectable levels of aflatoxins (defined as less than 5.0 ppb or the FGIS lower reporting level). This 92.5% is greater than the 77.8% of the 2012/13 export samples and 85.6% of the 2011/12 export samples.
- 25 samples or 6.1% of the 412 samples tested had aflatoxin levels greater than or equal to 5.0 ppb, but less than 10 ppb. This 6.1% is less than the 10.1% of the 2012/13 export samples and 8.1% of the 2011/12 export samples.
- 6 samples or 1.5% of the 412 samples tested had aflatoxin levels greater than or equal to 10.0 ppb, but less than the FDA action level of 20 ppb. This 1.5% is less than the 12.1% of the 2012/13 export samples and 6.3% of the 2011/12 export samples.
- 100% of the samples tested were below or equal to the FDA action level of 20 ppb, which are the same as the 2012/13 and 2011/12 export reports.
Note: Results for 46 of the 379 samples tested in 2011/2012 are excluded from the 2011/2012 distribution because the analytical method for aflatoxins used for the 2011/2012 survey did not allow the samples to be placed into ppb categories chosen for the 2013/2014 report. However, the test results for all 46 samples were below or equal to the FDA action level of 20 ppb.
Comparing the 2013/14 aflatoxin export survey results to the 2012/13 and 2011/12 export survey results suggests that there were fewer incidents of aflatoxins in 2013 than in either the 2012 and 2011 crop seasons. The higher proportion of samples with no detectable levels of aflatoxins in 2013 than in 2012 and 2011 may be due, in part, to more favorable weather conditions during the 2013 growing season when compared to similar environmental conditions during the 2012 and 2011 growing seasons. These results are consistent with the aflatoxin results from the Harvest Reports 2013/14, 2012/13 and 2011/12.
2. DON (Deoxynivalenol or Vomitoxin) Testing Results
A total of 412 export samples were tested for DON for the Export Cargo Report 2013/14. Results of the testing are shown below:
- 391 samples or 94.9% of the 412 samples tested had levels less than 0.5 ppm of DON. This 94.9% is less than the 97.5% of the 2012/13 export samples but greater than the 84.2% of the 2011/12 export samples.
- 21 samples or 5.1% of the 412 samples tested had DON levels greater than or equal to 0.5 ppm, but less than or equal to the FDA advisory level of 5 ppm. This 5.1% is greater than the 2.5% of the 2012/13 export samples but less than the 15.8% of the 2011/12 export samples.
- 100% of the samples tested were below or equal to the FDA advisory level of 5 ppm, which are the same as the 2012/13 and 2011/12 export reports.
Comparing the 2013/14 DON export survey results to the 2012/13 and 2011/12 DON export survey results indicates that there were less DON contaminations in the 2013 crop season than in the 2011 crop season and about the same as in the 2012 crop season. These results are consistent with the DON results for the Harvest Reports 2013/14, 2012/13 and 2011/12.
3. Mycotoxin Background: General
The levels at which the fungi produce mycotoxins are influenced by the fungus type and the environmental conditions under which the corn is produced and stored. Because of these differences, mycotoxin production varies across the U.S. corn-producing areas and across years.
Humans and livestock are sensitive to mycotoxins at varying levels. As a result, the U.S. Food and Drug Administration (FDA) has issued action levels for aflatoxins and advisory levels for DON by intended use.
- Action levels specify precise limits of contamination above which the agency is prepared to take regulatory action. Action levels are a signal to the industry that FDA believes it has scientific data to support regulatory and/or court action if a toxin or contaminant is present at levels exceeding the action level if the agency chooses to do so. If import or domestic feed supplements are analyzed in accordance with valid methods and found to exceed applicable action levels, they are considered adulterated and may be seized and removed from interstate commerce by FDA.
- Advisory levels provide guidance to the industry concerning levels of a substance present in food or feed that are believed by the agency to provide an adequate margin of safety to protect human and animal health. While FDA reserves the right to take regulatory enforcement action, enforcement is not the fundamental purpose of an advisory level.
A source of additional information is the National Grain and Feed Association (NGFA) guidance document titled “FDA Mycotoxin Regulatory Guidance” found at http://www.ngfa.org/wp-content/uploads/NGFAComplianceGuide-FDARegulatoryGuidanceforMycotoxins8-2011.pdf.
4. Mycotoxin Background: Aflatoxins
The most important type of mycotoxin associated with corn grain is aflatoxins. There are several types of aflatoxins produced by different species of the Aspergillus fungus, with the most prominent species being A. flavus. Growth of the fungus and aflatoxin contamination of grain can occur in the field prior to harvest or in storage. However, contamination prior to harvest is considered to cause most of the problems associated with aflatoxin. A. flavus grows well in hot, dry environmental conditions or where drought occurs over an extended period of time. It can be a serious problem in the southern United States, where hot and dry conditions are more common. The fungus usually attacks only a few kernels on the ear and often penetrates kernels through wounds produced by insects. Under drought conditions, it also grows down silks into individual kernels.
There are four types of aflatoxins naturally found in foods – aflatoxins B1, B2, G1 and G2.These four aflatoxins are commonly referred to as “aflatoxins” or “total aflatoxins.” Aflatoxin B1 is the most commonly found aflatoxins in food and feed and is also the most toxic. Additionally, dairy cattle will metabolize aflatoxins to a different form of aflatoxins called aflatoxin M1, which may accumulate in milk.
Aflatoxins are toxic in humans and animals by primarily attacking the liver. The toxicity can occur from shortterm consumption of very high doses of aflatoxincontaminated grain or long-term ingestion of low levels of aflatoxins, possibly resulting in death in poultry and ducks, the most sensitive of the animal species. Livestock may experience reduced feed efficiency or reproduction, and both humans’ and animals’ immune systems may be suppressed as a result of ingesting aflatoxins.
The FDA has established action levels for aflatoxins in milk intended for human consumption and for total aflatoxins in human food, grain and livestock feed products (see table below).
FDA has established additional policies and legal provisions concerning the blending of corn with levels of aflatoxins exceeding these threshold levels. In general, FDA currently does not permit the blending of corn containing aflatoxins with uncontaminated corn to reduce the aflatoxin content of the resulting mixture to levels acceptable for use as human food or animal feed.
Corn exported from the United States must be tested for aflatoxins according to Federal law. Unless the contract exempts this requirement, testing must be conducted by FGIS. Corn above the FDA action level of 20 ppb cannot be exported unless other strict conditions are met. These requirements result in relatively low levels of aflatoxins in exported grain.
5. Mycotoxin Background: DON (Deoxynivalenol) or Vomitoxin
DON is another mycotoxin of concern to some importers of corn grain. It is produced by certain species of Fusarium, the most important of which is F. graminearum (Gibberella zeae) which also causes Gibberella ear rot (or red ear rot). Gibberella zeae can develop when warm or moderate and wet weather occurs at flowering. The fungus grows down the silks into the ear, and in addition to producing DON, it produces conspicuous red discoloration of kernels on the ear. The fungus can also continue to grow and rot ears when corn is left standing in the field. Mycotoxin contamination of corn caused by Gibberella zeae is associated with excessively postponing harvest and/ or storing high-moisture corn.
DON is mostly a concern with monogastric animals where it may cause irritation of the mouth and throat. As a result, the animals may eventually refuse to eat the DON-contaminated corn and may have low weight gain, diarrhea, lethargy and intestinal hemorrhaging. It may cause suppression of the immune system resulting in susceptibility to a number of infectious diseases.
The FDA has issued advisory levels for DON. For products containing corn, the advisory levels are:
- 5 ppm in grains and grain by-products for swine, not to exceed 20% of their diet;
- 10 ppm in grains and grain by-products for chickens and cattle, not to exceed 50% of their diet; and
- 5 ppm in grains and grain by-products for all other animals, not to exceed 40% of their diet.
FGIS is not required to test for DON on corn bound for export markets, but will perform either a qualitative or quantitative test for DON at the buyer’s request.