A global evaluation of the impact of mycotoxins contaminants on food safety

What are mycotoxins?

Mycotoxins are poisonous substances produced by fungi – a group of organisms that contains moulds, yeasts and mushrooms. In particular, fumonisins and aflatoxins which are produced by molds of the genus Fusarium and Aspergillus respectively, are mycotoxins of public health significance.

Aflatoxins are known to cause cancer of the liver in humans, and fumonisins are thought to be possible cancer promoters of aflatoxin carcinogenicity. While the evidence for their adverse health effects in humans is currently inconclusive, there are concerns that exposure to fumonisins may contribute to various serious adverse health outcomes such as cancer, and birth defects. There is also some evidence and concern that there might be additive or synergistic actions that occur when both types of mycotoxins are present, potentially increasing their carcinogenicity.

Fumonisins can also have significant health effects in livestock and other animals and aflatoxins pose a significant economic burden, causing an estimated 25% or more of the world’s food crops to be destroyed annually.

What are the food products that can contain mycotoxins?

Several types of aflatoxin (14 or more) occur in nature, but four – aflatoxins B1, B2, G1 and G2 - are particularly dangerous to humans and animals.

A number of different types of fumonisins are also known, but fumonisins B1, B2 and B3 are the major forms found in food.

Fumonisins and aflatoxins are frequent contaminants of maize and, to a lesser extent, of rice, sorghum, wheat, and cereal-based foods prepared from these commodities. Food crops can become contaminated both before and after harvesting. Aflatoxins, but not fumonisins, are also common contaminants of ground nuts (e.g. peanuts) and tree nuts (e.g. almonds, pistachios, Brazil nuts).

Dairy milk and its processed products may also be contaminated, following the geographic pattern of contamination of aflatoxins.

These two mycotoxins occur worldwide, but exposure to both is more likely in areas where these foods are routinely consumed. Co-exposure can either occur from the same food being contaminated with both mycotoxins, or within diets or meals from different foods, each contaminated with one or the other.

What are the consequences of exposure to mycotoxins to human health?

Acute poisoning at high contamination levels of aflatoxins can be life threatening. Aflatoxins are also among the most carcinogenic and mutagenic (DNA damaging) substances known, and they cause immunosuppression and possibly stunting.

Fumonisins are associated with a wide range of health effects in animals, especially on the liver and kidney, however the data currently available for the health effects of fumonisins in humans are limited.

Regarding aflatoxin–fumonisin interactions, the co-occurrence of the two types of mycotoxins could include possible antagonistic, additive or synergistic effects. However, there is not yet adequate information to facilitate an understanding of the role and extent of such co-exposure as a contributing factor in some human diseases. Since there are also few reports on dietary co-exposure, it is difficult to have a clear picture of these risks.

What are the problems with mycotoxins detection and sampling?

Detecting aflatoxicosis (acute aflatoxin poisoning) in humans and animals is difficult due to variations in clinical signs and the presence of confusing factors such as suppression of the immune system caused by an infectious disease.

To detect aflatoxins in food and feed, a variety of methods are available. However, since the distribution of molds is not even in bulk shipments and stored grain, a proper sampling procedure is very important to ensure a representative sample. These recommended sampling methods are a problem especially for subsistence farmers in rural areas who do not produce enough grain to spare the quantities needed for accurate testing. Thus, there is a need to develop for aflatoxins, rapid, low-cost, low technology, accurate detection methods in order to improve surveillance and control in rural areas.

To detect fumonisins in maize and maize by-products, many methods have been developed. Some of these methods are expensive and laborious. However, studies to develop a fumonisin detection procedure that is simple, rapid, and inexpensive are ongoing.

How can mycotoxins be controlled in the food supply?

Overall, an integrated (or systemic) approach, whereby aflatoxins are controlled at all stages from the field to the table, is required for reducing the possibility of mycotoxins contamination.

Both pre and post-harvest control measures are available but better procedures are required.

• Pre-harvest controls include plant breeding practices, enhancement of host plant resistance, transgenic crops, and biological control methods. Particularly for aflatoxins, biological control – where another, non-toxic mold is introduced into the field to take the place of the toxic varieties – is already showing promise.
• Post-harvest technologies include proper drying and storage of potentially affected crop products, as well as development of appropriate alternative uses to retain at least some economic return on value of any damaged crop. 

What can national authorities do with the support of WHO to reduce food contamination by mycotoxins?

WHO, in collaboration with FAO, analyses the scientific knowledge available and evaluates the risk in order to define safe exposure levels. Based on these risk assessments, maximum levels for aflatoxins and fumonisins in different foods are recommended.

These elements form the basis for the Codex Alimentarius Commission, which creates harmonized international food safety standards to protect the health of consumers and ensure fair trade practices.

• For aflatoxins, in various nuts, grains, dried figs and milk the maximum levels of contamination allowed are in the range of 0.5 to 15 μg/kg. 
• For fumonisins, the maximum levels in grain from raw maize and in maize flour and meal are 4000 and 2000 μg/kg respectively.

To prevent and reduce the risk of aflatoxin in food for humans or animals, the Codex Commission has also developed a Code of practice, which describes in detail appropriate preventive measures.

These Codex Alimentarius recommendations, their maximum levels, and Code of practice serve then as guidance for national authorities for their regulations to limit mycotoxins contamination.

What can consumers do to protect themselves against mycotoxins exposure?

As fumonisins and aflatoxins do not always occur in the same food, WHO has developed specific recommendations on how to avoid each of these mycotoxins in the diet.

Some foods are potentially contaminated with moulds producing aflatoxins which do not just grow on the surface but penetrate deep into food which are therefore possibly harmful when consumed.

Maize will occasionally be contaminated with fumonisins, and consumers living on a maize-based staple diet need to pay extra attention to minimize exposure to these toxins. But since most measures to avoid fumonisins contamination take place before harvest, the consumer has only few opportunities to minimize this possibility of exposure.

To reduce exposure to aflatoxins and fumonisins, the consumer is advised to:

• buy maize, wheat and other grains, butter and nuts as fresh as possible and only from reputable brands; 
• carefully inspect whole grains and nuts for evidence of mould, and discard any that look mouldy, discoloured, or shriveled; 
• buy grains and nuts as fresh as possible; 
• make sure that foods are stored properly and are not kept for extended periods of time before being used;  
• try to ensure his/her diet is diverse.

References:
Aflatoxins – Food Safety Digest, WHO, 2018 www.who.int/foodsafety/Food_Safety_Digest_Aflatoxins_EN.pdf?ua=1
Fumonisins – Food Safety Digest, WHO, 2018 www.who.int/foodsafety/Food_Safety_Digest_Fumonisins_EN.pdf?ua=1
Co-exposure to Fumonisins and Aflatoxins – food Safety Digest, WHO, 2018 www.who.int/foodsafety/Food_Safety_Digest_Fumonisins_aflatoxins_EN.pdf?ua=1
including elements of the report: Evaluation of certain contaminants in food: eighty-third report of the Joint FAO/WHO Expert Committee on Food Additives. WHO technical report series ; no. 1002, 2017. http://apps.who.int/iris/bitstream/10665/254893/1/9789241210027-eng.pdf