What is Aflatoxin?

Aflatoxin is a naturally occurring toxin produced by certain types of mould. It can be found on various food crops, including maize/corn, peanuts, and tree nuts. Aflatoxin can occur through ingestion of contaminated food or inhalation of contaminated dust.

Health Risks

Aflatoxin is a potent carcinogen, meaning it can increase the risk of developing cancer. Exposure to high of aflatoxin can also lead to liver damage, liver cancer, and even death. A number of countries have strict regulations in place to limit the amount of aflatoxin in food.

Mycotoxins and Their Importance

Aflatoxin is a type of mycotoxin—a poison produced by a fungus or mould that colonizes crops. These toxic compounds are secondary metabolites, meaning they aren’t directly involved in the normal growth, development, or reproduction of the organism. Different fungi produce various mycotoxins, which can cause disease and death in humans and livestock. Important mycotoxins include:

• Aflatoxin
• Ergot
• Fumonisins
• Ochratoxin
• Deoxynivalenol
• Zearalenone

Discovery of Aflatoxin

In 1960, more than 100,000 turkeys in England died from a condition called Turkey X Disease. Ducklings and pheasants showed similar symptoms, and the source was traced to contaminated peanut meal feed. In 1961, the common soil fungus Aspergillus flavus was identified as the cause. The toxin it produced was named aflatoxin.

Types of Aflatoxin

There are six main types of aflatoxin based on their chemical structures, which fluoresce differently under UV light:

• Aflatoxins G1 & G2: Fluoresce yellow-green
• Aflatoxins B1 & B2: Fluoresce blue

All four types are produced by Aspergillus flavus and Aspergillus parasiticus, although the fungi may produce varying concentrations of the toxin. Aflatoxins M1 and M2 are derived from B1 and B2, and are found in the milk of lactating animals that consume contaminated feed. Aflatoxin B1 is the most toxic of these and is of the highest concern.

Fungi Producing Aflatoxin

Aflatoxin is produced by several soil-borne fungi or moulds, with Aspergillus flavus being the most notable. Other fungi such as Aspergillus parasiticus, Aspergillus nomius, and Aspergillus niger can also produce aflatoxin. These fungi are prevalent worldwide, especially in tropical regions.

Aflatoxin production is not essential for the fungus to grow, making it a secondary metabolite. While its exact role is still under research, it’s believed that aflatoxin helps fungi survive during stressful conditions like temperature and water stress. However, the amount of aflatoxin produced varies widely, leading scientists to study why some strains are non-toxigenic and why toxin levels can fluctuate.

Conditions Conducive for Aflatoxin

The Aspergillus fungi that produce aflatoxin are naturally present in soil, posing a significant risk to groundnuts (since the nut grows underground) and other crops in almost any climate, especially hot and humid environments. Factors contributing to high aflatoxin levels include:

• End of season drought
• Insect and mechanical damage to nuts
• Insufficient crop drying
• Poor storage conditions

Health Impacts

Aflatoxin is odorless and tasteless. While the mould that produces the toxin can be visually identified, the toxin itself is invisible. Even minute amounts can cause severe health problems in humans and livestock. Acute aflatoxin poisoning (toxicosis), resulting from high-level exposure over a short period, can cause liver and kidney damage, leading to jaundice. Lower levels of exposure over a prolonged period can lead to liver cancer, with aflatoxin causing approximately 25% of global liver cancer cases. It can also exacerbate health issues related to hepatitis B and HIV-AIDS.

Safety Standards and Regulations

While it is difficult to eliminate aflatoxin completely from foods and feed, many organizations and countries have set limits on the allowable amounts. In the U.S., the USDA and the National Grain and Feed Association have established minimum total aflatoxin levels for food and feed.

U.S. Department of Agriculture standards, National Grain and Feed Association, 2014

The EU has set a limit of 4 parts per billion (ppb) for total aflatoxins in human food and 20 ppb for aflatoxin B1 in animal feed. These limits, expressed in the ppb range, involve extremely low amounts—comparable to one grain of rice in a 50 kg bag or one drop of water in a swimming pool. Ppb can also be expressed as µg/kg (microgram per kilogram).