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 sorghum 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 sorghum value chain – seed companies, sorghum growers, grain marketers and handlers, as well as U.S. sorghum 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. sorghum export system.
ASSESSING THE PRESENCE OF AFLATOXINS AND DON
To assess the effect of the above-mentioned conditions on aflatoxins and DON development, this report summarizes the results from offcial U.S. Department of Agriculture (USDA) Federal Grain Inspection Service (FGIS) aflatoxin tests and from independent aflatoxin and DON tests for all the export samples collected as part of this survey.
A threshold established by FGIS as the “Lower Conformance Level” (LCL) was used to determine whether or not a detectable level of the mycotoxin appeared in the sample. The LCL for the analytical kits approved by FGIS and used for this 2015/2016 Export Cargo Survey was 5.0 parts per billion (ppb) for aflatoxins and 0.5 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.
A total of 182 export samples were analyzed for aflatoxins for the 2015/2016 Export Cargo Survey. Results of the 2015/2016 survey are as follows:
- One hundred seventy-five (175) samples or 96.2% of the 182 samples tested in 2015/2016 had no detectable levels of aflatoxins (defined as less than or equal to the FGIS LCL limit of 5 parts per billion (ppb)).
- Five (5) samples or 2.7% of the 182 samples tested in 2015/2016 had aflatoxin levels greater than 5 ppb, but less than or equal to 10 ppb.
- Two (2) samples or 1.1% of the 182 samples tested in 2015/2016 had aflatoxin levels greater than 10 ppb, but less than or equal to the Food and Drug Administration (FDA) action level of 20 ppb.
- 100% of the samples tested in 2015/2016 were below the FDA action level of 20 ppb.
Most sample test results (98.9%) were less than or equal to 10 ppb, and a high percentage of sample test results (96.2%) were less than the FGIS LCL of 5.0 ppb.
RESULTS: DON (DEOXYNIVALENOL OR VOMITOXIN)
A total of 182 export samples were tested for DON for the 2015/2016 Export Cargo Survey. Results of the testing are shown below:
- All one hundred and eighty-two (182) samples, or 100.0%, had no detectable levels of DON (all samples tested less than or equal to the FGIS LCL of 0.5 ppm).
- None of the sample test results (0), or 0.0% of the 182 samples, tested greater than 0.5 ppm, but less than or equal to the FDA advisory level of 5 ppm.
- None of the sample test results (0), or 0.0% of the 182 samples, tested greater than the FDA advisory level of 5 ppm.
1. Background: General
The levels at which the fungi produce mycotoxins are influenced by the fungus type and the environmental conditions under which the sorghum is produced and stored. Because of these differences, mycotoxin production varies across the U.S. sorghum-producing areas and across years.
Humans and livestock are sensitive to mycotoxins at varying levels. As a result, the 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 scientifc 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”, which can be found at http://www.ngfa.org/wp-content/uploads/NGFAComplianceGuide-FDARegulatoryGuidanceforMycotoxins8-2011.pdf.
2. Background: Aflatoxins
The most important type of mycotoxin associated with sorghum 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 plant and often penetrates kernels through wounds produced by insects.
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 type of aflatoxin in food and feed and is also the most toxic. Additionally, dairy cattle metabolize aflatoxins to a different form of aflatoxin called aflatoxin M1, which may accumulate in milk.
Aflatoxins express toxicity in humans and animals primarily by 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 effciency or reproduction, and both humans’ and animals’ immune systems may be suppressed due to aflatoxin ingestion.
The FDA has established action levels for aflatoxin M1 in milk intended for human consumption and for total aflatoxins in human food, grain and livestock feed products (see table below).
The FDA has established additional policies and legal provisions concerning the blending of grain with levels of aflatoxins exceeding these threshold levels. In general, FDA currently does not permit the blending of grain containing aflatoxins with uncontaminated grain to reduce the aflatoxin content of the resulting mixture to levels acceptable for use as human food or animal feed.
If required by the buyer, sorghum exported from the United States will be tested for aflatoxins by FGIS. Sorghum above the FDA action level of 20 ppb or the buyer’s specifcation cannot be exported unless other strict conditions are met. These requirements result in relatively low levels of aflatoxins in exported grain.
3. Background: DON (Deoxynivalenol or Vomitoxin)
DON is another mycotoxin of concern to some importers of sorghum grain. It is produced by certain species of Fusarium, the most important of which is F. graminearum (Gibberella zeae). Gibberella zeae can develop when cool or moderate and wet weather occurs at flowering. Mycotoxin contamination of sorghum caused by Gibberella zeae is often associated with excessive postponement of harvest and/or storage of high-moisture sorghum.
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 sorghum and may have low weight gain, diarrhea, lethargy and intestinal hemorrhaging. Additionally, DON 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 sorghum, 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 sorghum bound for export markets, but will perform either a qualitative or quantitative test for DON at the buyer’s request.