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.
As in 2011 and 2012, the 2013 harvest samples were tested for aflatoxins and DON for this year’s report. Since the production of mycotoxins is heavily influenced by growing conditions, the objective of the Harvest Quality Reports is strictly to report on instances when aflatoxins or DON are detected in the corn crop at harvest. No specific levels of the mycotoxins are reported.
The Harvest Quality Reports review of mycotoxins is NOT intended to predict the presence or level at which mycotoxins might appear in U.S. corn exports. Due to the multiple stages of the U.S. grain merchandising channel and the laws and regulations guiding the industry, the levels at which mycotoxins appear in corn exports are less than what might first appear in the corn as it comes out of the field. In addition, this report is not meant to imply that this assessment will capture all the instances of mycotoxins across the 12 states or three Export Catchment Areas (ECAs) surveyed. The Harvest Quality Reports results should be used only as one indicator of the potential for mycotoxin presence in the corn as the crop comes out of the field. As the Council accumulates several years of the Harvest Quality Reports, year-to-year patterns of mycotoxin presence in corn at harvest will be seen. The U.S. Grains Council Corn Export Cargo Quality Report 2013/14 will report corn quality at export points and will be a more accurate indication of mycotoxin presence in the 2013/14 U.S. corn export shipments.
1. Assessing the Presence of Aflatoxins and DON
A weighted and systematic testing at least 25% of the targeted 600 samples across the entire sampled area was conducted to assess the impact of the 2013 growing conditions on total aflatoxins and DON development in the U.S. corn crop. The sampling criteria, described in the “Survey and Statistical Analysis Methods” section, resulted in a targeted number of 179 samples tested for mycotoxins.
A threshold referred to as the Limit of Detection (LOD) was used to determine whether or not a detectable level of the mycotoxin appeared in the sample. The LOD for the analytical kits used for this 2013/14 report was 2.5 parts per billion (ppb) for aflatoxins and 0.3 parts per million (ppm) for DON. Details on the testing methodology employed in this study for the mycotoxins are in the “Testing Analysis Methods” section.
2. Aflatoxins Testing Results
A total of 179 samples were analyzed for aflatoxins in 2013. This is about the same number of samples (177) tested for aflatoxins in 2012. Results of the 2013 survey are as follows:
- One hundred seventy six (176) samples, or 98.3% of the 179 samples, had no detectable levels of aflatoxins (below the 2.5 ppb LOD). In 2012 and 2011, 78.0% and 97.9% of the samples tested had no detectable levels of aflatoxins, respectively.
- One sample, or 0.6% of the 179 samples, showed aflatoxin levels greater than or equal to the LOD of 2.5 ppb, but less than 5 ppb.
- No samples, or 0.0% of the 179 samples, showed aflatoxin levels greater than or equal to 5 ppb, but less than 10 ppb.
- One sample, or 0.6%, of the 179 samples, showed aflatoxin levels greater than or equal to 10 ppb, but less than or equal to the FDA action level of 20 ppb.
- These results denote that 178 samples, or 99.4% of the 179 sample test results in 2013, were below or equal to the FDA action level of 20 ppb, compared to 88.1% and 97.9% of the samples tested in 2012 and 2011, respectively.
- One sample, or 0.6% of the 179 samples, tested above the FDA action level of 20 ppb. The 2012 and 2011 percentage for samples with aflatoxin levels exceeding 20 ppb were 11.9% and 2.1%, respectively.
Comparing the 2013 aflatoxin survey results to the 2012 and 2011 results suggests that there were fewer incidents of aflatoxins among all Agricultural Statistical Districts (ASDs) in 2013 than in the 2012 crop seasons and about the same as in 2011. The lower proportion of samples with aflatoxin levels exceeding the FDA action level in 2013 and 2011 than in 2012 may be due, in part, to more favorable (less stressful) weather conditions when compared to similar environmental conditions in 2012 (see the “Crop and Weather Conditions” section for more information on the 2013 growing conditions). Weather during spring 2013 and 2011 was cool and wet compared to a more extensive drought in 2012.
3. DON (Deoxynivalenol or Vomitoxin) Testing Results
A total of 179 samples were analyzed collectively for DON in 2013. This is about the same number of samples (177) tested for aflatoxins in 2012. Results of the 2013 survey are shown below: One hundred sixty four (164) samples, or 91.6% of the 179 samples, tested less than the 0.5 ppm.
- Fifteen (15) samples, or 8.4% of the 179 samples, tested greater than or equal to 0.5 ppm, but less than or equal to the FDA advisory level of 5 ppm.
- All 179 samples, or 100%, tested below or equal to the FDA advisory level of 5 ppm.
- The 2013 percentage for samples that tested below 0.5 ppm (91.6%) is about the same as in 2012 (96.0%), but higher than the 78.7% observed in 2011.
- In 2013, 100% percent of the samples tested at or below 5 ppm, which is the same as was observed in 2012 and 2011. Comparing the 2013 DON survey results to 2012 and 2011 survey results indicates that there were less DON contaminations in 2013 than in the 2011 crop season and about the same as in the 2012 crop season.
4. Mycotoxin Background: General
The levels at which the fungi produce the mycotoxins are impacted 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. In some years, the growing conditions across the corn production regions might not produce elevated levels of any mycotoxins. While in other years, the environmental conditions in a particular area might be conducive to production of a particular mycotoxin to levels that impact the corn’s use for human and livestock consumption. Humans and livestock are sensitive to mycotoxins at varying levels. As a result, the U.S. Food and Drug Administration (FDA) have 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 Regulatory Guidance for Toxins and Contaminants” found at http://www.ngfa.org/ wp-content/uploads/NGFAComplianceGuide-FDARegu latoryGuidanceforMycotoxins8-2011.pdf.
5. Mycotoxin Background: Aflatoxins
The most important type of mycotoxin associated with corn grain is aflatoxin. There are several types of aflatoxin produced by different species of Aspergillus 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 aflatoxin 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 aflatoxin in food and feed and is also the most toxic. Research has shown that B1 is a potent naturally occurring carcinogen in animals, with a strong link to human cancer incidence. Additionally, dairy cattle will metabolize aflatoxin to a different form of aflatoxin 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 short-term consumption of very high doses of aflatoxin-contaminated 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 aflatoxin M1 in milk intended for human consumption and aflatoxins in human food, grain and livestock feed (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 aflatoxin 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. This results in relatively low levels of aflatoxins in exported grain.
6. Mycotoxin Background: DON (Deoxynivalenol) or Vomitoxin
DON is another mycotoxin of concern to some importers of corn. It is produced by certain species of Fusarium, the most important of which is Fusarium graminearum (Gibberellazeae) which also causes Gibberella ear rot (or red ear rot). Gibberellazeae 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 Gibberellazeae 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 co-products for swine, not to exceed 20% of their diet,
- 10 ppm in grains and grain co-products for chickens and cattle, not to exceed 50% of their diet, and
- 5 ppm in grains and grain co-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.