Aflatoxin M1 (AFM1) is a mycotoxin, a naturally occurring toxin produced by certain molds, that can be found in milk. Its presence is a food safety concern because dairy products are widely consumed by people of all ages. The toxin enters the food supply when livestock consume contaminated feed, making it an issue that connects agriculture and animal health.
The Origin of Aflatoxin M1
Aflatoxin M1’s story begins in fields where specific molds, primarily Aspergillus flavus and Aspergillus parasiticus, grow on agricultural commodities. These molds thrive in warm, humid climates and are frequently found on crops used in livestock feed, such as corn, cottonseed, and peanuts. Under these conditions, the fungi produce a parent toxin known as aflatoxin B1 (AFB1), a potent carcinogen.
The pathway into milk is a biological process within the dairy animal. When a lactating animal consumes feed contaminated with AFB1, the toxin is absorbed into its bloodstream and transported to the liver. Inside the liver, metabolic processes convert AFB1 into its metabolite, aflatoxin M1.
A portion of this AFM1 is then secreted into the animal’s milk. The process from ingestion of contaminated feed to the appearance of AFM1 in milk can happen within 12 to 24 hours. The amount of AFM1 in the milk is directly related to the concentration of AFB1 in the feed, with studies showing that approximately 0.3% to 6.2% of the ingested AFB1 is transferred into milk as AFM1.
Foods Contaminated with Aflatoxin M1
The primary vehicle for human exposure to Aflatoxin M1 is milk from animals that have ingested contaminated feed. While the focus is on cow’s milk due to its global prevalence, this can also include milk from goats and sheep. The presence of AFM1 is not limited to liquid milk; it is also found in dairy products made from contaminated milk, including cheese, yogurt, butter, and milk powder.
Because AFM1 is a stable compound, it persists through processing. Its resistance to heat means that pasteurization and other thermal treatments do not eliminate or reduce the toxin’s concentration. This stability ensures that if the raw milk is contaminated, the resulting dairy products will be as well.
This presents a concern for infant formula, which is often milk-based. The stability of the toxin means that powdered formulas can still pose an exposure risk if the original milk source was contaminated.
Health Risks and Vulnerable Populations
The International Agency for Research on Cancer (IARC) classifies AFM1 as a Group 1 carcinogen, meaning it is carcinogenic to humans. The primary health risk from long-term exposure is an increased risk of liver cancer. AFM1 is also genotoxic, as it can damage DNA, which may lead to mutations and cancer.
While the liver and kidneys are especially susceptible, aflatoxins can impact all organ systems. Although AFM1 is less potent than its parent compound, AFB1, its presence in a dietary staple like milk makes human exposure a significant issue. Exposure has also been linked to immunosuppression, which can weaken the body’s ability to fight off infections.
Infants and young children are the most vulnerable population. Their high consumption of milk relative to their body weight means they can ingest a proportionally larger dose of the toxin. Additionally, their developing metabolic systems may struggle to process and eliminate toxins effectively. This combination places them at greater risk for adverse health effects, including stunted growth and delayed development.
Regulation and Safety Standards
To manage the risks associated with Aflatoxin M1, regulatory agencies around the world have established strict limits for its presence in milk and dairy products. In the United States, the Food and Drug Administration (FDA) has set an action level of 0.5 parts per billion (ppb) for AFM1 in milk intended for human consumption. Milk found to contain levels exceeding this limit is considered adulterated and cannot be sold.
These regulatory efforts extend to the animal feed itself. The FDA also stipulates a maximum level of 20 ppb for aflatoxin B1 in feed for lactating dairy cattle to control the toxin at its source. By limiting the amount of the parent toxin in animal diets, the subsequent contamination of milk with AFM1 is minimized.
Regulatory standards can vary internationally, reflecting different risk assessments. The European Union, through the European Food Safety Authority (EFSA), has implemented more stringent limits. The maximum level for AFM1 in raw milk, heat-treated milk, and milk for the manufacture of milk-based products is set at 0.05 µg/kg. For infant formulae and follow-on formulae, the EU limit is even lower, at 0.025 µg/kg, due to the heightened vulnerability of this population.