Mycotoxins are toxic compounds produced by fungi that occur naturally in grains. When consumed at elevated levels, mycotoxins may cause sickness in animals and humans. 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 2011 Harvest Report assesses the presence of measurable levels of these two mycotoxins in corn at harvest. 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 at harvest are not the same as what might appear in export cargoes. Therefore, the objective of the 2011 Harvest Report is strictly to report on instances when aflatoxins or DON were detected in some of the samples. No specific levels of the mycotoxins are reported.
The Harvest Report review of mycotoxins is NOT intended to predict the presence or level at which mycotoxins might appear in U.S. corn exports. In addition, this report is not meant to imply that this assessment will capture all the instances of mycotoxins across the twelve states surveyed. The Harvest Report results should be used only as one indicator of the potential for mycotoxin infection. Over several years, the Harvest Reports will reflect the year-to-year pattern of mycotoxin presence in corn as the crop comes out of the field. The Export Cargo Report, which reports corn at export points, will be a more accurate indication of mycotoxin presence in U.S. corn export shipments.
Assessing The Presence oF Aflatoxins and Don
While the U.S. grain merchandising industry implements strict safeguards for handling and marketing any elevated levels of mycotoxins, interest has been expressed for early detection of mycotoxins resulting from the growing conditions during the current crop year. To assess the impact of the 2011 growing conditions on total aflatoxins and DON development, random testing of samples across the entire sampled area was conducted. One to four samples from each ASD were tested for the mycotoxins, depending on the total number of samples collected from each ASD (See the “Survey and Statistical Analysis Methods” section for explanation of ASDs.). If multiple samples were tested within an ASD, the samples came from different elevators.
A threshold referred to as the Limit of Detection (LOD) was used to determine whether or not an instance of the mycotoxin appeared in the sample. The LOD used for this report was 2.5 parts per billion (ppb) for aflatoxins and 0.5 parts per million (ppm) for DON. If any sample for either mycotoxin exceeded the respective LOD, a different sample in the same ASD was tested for the same mycotoxin. This was done for additional verification of the presence of the mycotoxin at an elevated level. Details on the testing methodology employed in this study for the mycotoxins are in the “Testing Analysis Methods” section.
A total of 95 samples were analyzed for aflatoxins. All but two samples were below the LOD of 2.5 ppb. The remaining two sample test results were also above the FDA action limit of 20 ppb. The two samples with results above the LOD came from an area that had very hot and dry environmental conditions that would have favored the production of aflatoxins.
A total of 94 samples were tested for DON, and seventy-four of the samples were below the LOD of 0.5 ppm. However, all the samples contained DON levels below the FDA advisory level of 5.0 ppm. Most of the samples that were above the LOD of 0.5 ppm for DON were from corn growing areas where the weather was cool and wet during silking.
Mycotoxin Background: General
The levels at which the fungi produce the mycotoxins are impacted by the fungus type, and the 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 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, and 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 Regulatory Guidance for Toxins and Contaminants” found at http://www.ngfa.org/files/misc/Guidance_for_Toxins.pdf.
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 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 system may be suppressed as a result of ingesting aflatoxins.
The FDA has established action levels for aflatoxins in human food, grain and livestock feed products and aflatoxin M1 in milk intended for human consumption if the levels exceed: 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 U.S. must be tested for aflatoxins. Unless the contract allows for independent laboratory testing, the testing must be conducted by the USDA/GIPSA’s Federal Grain Inspection Service (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.
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 Fusarium graminearum (Gibberella zeae) which also causes Gibberella ear rot (or red ear rot). The fungus can be spotted easily in corn because of the conspicuous red discoloration of kernels on the ear. The presence of Gibberella zeae is mostly a problem when warm, wet weather occurs at flowering. The fungus grows down the silks into the ear, and in addition to producing DON, it results in damage to kernels that are evident during the grain inspection process. DON and Gibberella ear rot is most common in the northern Corn Belt states. This may be due to the susceptibility of very early maturing corn hybrids commonly grown in these areas to the fungus.
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.