What is aflatoxin B1?
Aflatoxin B1 is the most potent naturally occurring carcinogen known, and the mycotoxin with the strictest regulatory limits worldwide. This page covers where it comes from, what it does, what the limits are, and how it is measured.
Last reviewed 2026-11-11 · compiled by TripleBond Scientific Inc., Guelph, Ontario
Where it comes from
Aflatoxin B1 (AFB1, CAS 1162-65-8) is a difuranocoumarin produced mainly by Aspergillus flavus and Aspergillus parasiticus. These are warm-climate storage fungi, so aflatoxin contamination is driven as much by drying and storage conditions as by what happens in the field: moisture, temperature and insect damage during storage are the classic risk factors.
It occurs together with aflatoxins B2, G1 and G2, which is why most regulations set a limit on AFB1 individually and on the sum of all four. When a dairy animal eats AFB1-contaminated feed, it excretes the hydroxylated metabolite aflatoxin M1 in milk, which carries its own separate limits.
Commodities most affected
Maize, groundnuts (peanuts), tree nuts including pistachios, almonds and Brazil nuts, dried figs and other dried fruit, spices such as chilli and paprika, cottonseed, and the compound feeds made from them.
Why it is regulated so tightly
The International Agency for Research on Cancer classifies aflatoxins (B1, B2, G1, G2 and M1 as a naturally occurring mixture) in Group 1, carcinogenic to humans. Aflatoxin B1 is the most potent member of the group.
The mechanism is genotoxic. AFB1 is activated in the liver, principally by cytochrome P450 enzymes, to the reactive AFB1-8,9-epoxide, which forms DNA adducts. Chronic exposure is associated with hepatocellular carcinoma, and the risk is substantially higher in people who are also chronically infected with hepatitis B. Very high acute exposures cause aflatoxicosis, with acute liver failure.
Because the effect is genotoxic and carcinogenic, no tolerable daily intake is set for aflatoxins. Risk managers instead apply the ALARA principle: exposure is kept as low as reasonably achievable, and maximum levels are set at the lowest level that is analytically and practically enforceable.
Regulatory limits in brief
These are the headline figures. The full tables, with every commodity category and the source regulation for each number, are on our mycotoxin limits page.
- European Union. Legally binding maximum levels under Regulation (EU) 2023/915, typically 2 to 12 µg/kg for AFB1 depending on the commodity and whether it is destined for direct consumption, with separate levels for the sum of B1, B2, G1 and G2, and 0.025 µg/kg for aflatoxin M1 in raw milk.
- United States. FDA action levels, which are enforcement policy rather than regulation: 20 ppb total aflatoxins in food for human consumption, and 0.5 ppb aflatoxin M1 in milk.
- Canada. 20 ppb aflatoxin B1 in livestock feed, which is the one mycotoxin level in the CFIA's RG-8 guidance that is a legislated standard rather than a guideline.
How laboratories measure it
Two routes dominate. HPLC with fluorescence detection after immunoaffinity column clean-up remains a reference approach; because AFB1 and AFG1 fluoresce weakly in water-based mobile phases, post-column derivatisation — photochemical, or with bromine or iodine — or pre-column derivatisation with trifluoroacetic acid is used to enhance the signal. LC-MS/MS is now the method of choice for multi-mycotoxin panels, where aflatoxins are determined alongside deoxynivalenol, zearalenone, fumonisins and ochratoxin A in a single run. ELISA and lateral-flow kits are widely used for rapid screening at grain intake.
All three depend on a reference standard of known identity and purity. Calibration curves, recovery checks, spiking studies and method validation are only as good as the material the calibration is built on, which is why the purity specification and the analytical evidence supplied with a standard matter more than the price per milligram.
Aflatoxin B1 reference standard
Produced in our own Canadian laboratory, from analytical quantities through to gram and kilogram scale. Catalogue pricing is published for analytical sizes.
See the standard →Common questions
Is aflatoxin B1 a carcinogen?
Yes. IARC classifies aflatoxins, including aflatoxin B1, in Group 1: carcinogenic to humans. Aflatoxin B1 is the most potent of the group and is associated with hepatocellular carcinoma, with a substantially higher risk in people chronically infected with hepatitis B.
What is the difference between aflatoxin B1 and aflatoxin M1?
Aflatoxin M1 is a hydroxylated metabolite of aflatoxin B1. When a dairy animal consumes feed contaminated with aflatoxin B1, M1 is excreted in the milk, which is why milk has its own separate and much lower limits.
Which fungi produce aflatoxin B1?
Mainly Aspergillus flavus and Aspergillus parasiticus. They are warm-climate fungi and contamination is strongly influenced by drying and storage conditions, not only by field conditions.
Is there a tolerable daily intake for aflatoxin?
No. Because aflatoxins are genotoxic carcinogens, no tolerable daily intake is set. Exposure is managed under the ALARA principle, with maximum levels set as low as is reasonably achievable.
What purity does an aflatoxin B1 reference standard need?
It depends on the application. Calibration for a regulatory method needs documented identity and purity; a spiking study or recovery experiment may have different requirements. The specification should be agreed against the method, not assumed from a catalogue line.
Sources
- IARC Monographs, Agents Classified by the IARC Monographs
- Commission Regulation (EU) 2023/915 on maximum levels for certain contaminants in food
- US FDA, Guidance for Industry: Action Levels for Poisonous or Deleterious Substances
- Canadian Food Inspection Agency, RG-8 Regulatory Guidance: Contaminants in Feed