Mycotoxins in a Changing Climate

Global climate change is an issue we should take very seriously now or it will threaten our future food supply. However, I am writing this in June 2020 in the middle of the coronavirus pandemic that is attracting all the attention. There are so far more than 6 million people affected worldwide and soon more than 400,000 deaths.

Most countries, but not all, have reacted with urgency to the acute situation with people movements severely restricted and huge amounts of money spent to support economies. More than one hundred attempts to develop vaccines agains the COVID-19 disease are under way to prevent future outbreaks.

Willingness to limit climate change lacking

We already have the “vaccines” or knowhow to prevent further escalation of the changing climate. Although climate change in the longer term will threaten food security, that is global access to food, and negatively impact food safety with the potential to cause much more pain and suffering, hunger and deaths, it is not getting the same attention as a novel acute disease.

There are many pathways through which climate related factors may impact food safety including: changes in temperature and precipitation patterns, increased frequency and intensity of extreme weather events, ocean warming, and changes in the transport pathways of complex contaminants.

Food security might be the more serious challenge as sufficient access to nutritious food is already an issue in many parts of the world, but long-term quality of life is also threatened by food contamination. We have already covered accumulation of arsenic as an example of heavy metal increases in food caused by climate change. Here we will cover aflatoxin as an example of an increased threat from a range of mycotoxins as fungal growth is influenced by climate change.

Mycotoxin threat will increase

Mycotoxins are compounds naturally produced by a large variety of fungi (moulds) that can cause acute effects, including death, along with chronic illnesses from long-term exposure, including various forms of cancer. It has been estimated that 25% of the world’s yearly crop production is already contaminated with mycotoxins. Mycotoxins are known to occur more frequently in areas with a hot and humid climate.

Aflatoxins, which have the highest acute and chronic toxicity of all mycotoxins, assume particular importance. Aflatoxin produced by Aspergillus flavus and A. parasiticus is a genotoxic carcinogen, but is also a potent acute toxin, and is widely distributed associated especially with maize, groundnuts, tree nuts, figs, dates and certain oil seeds such as cottonseed.

Aflatoxins are a group of approximately 20 related fungal metabolites. They are heat stable and difficult to destroy during processing. Thus exposure, both acute and chronic, can have significant impacts on vulnerable groups, especially babies and children. Four aflatoxins – B1, B2, G1 and G2 – are particularly dangerous to humans and animals.

Health effects of aflatoxin exposure

Outbreaks of acute aflatoxicosis were reported in Kenya in 2004 with 125 deaths resulting from consumption of aflatoxin contaminated maize with repeated events in 2005 and 2006. Most recently several deaths attributed to aflatoxins were reported during the summer of 2016 in the United Republic of Tanzania.

However, chronic effects are much more common. Hepatocellular carcinoma, or liver cancer, is the third leading cause of cancer deaths worldwide, with prevalence 16-32 times higher in developing countries than in developed countries. Of the 550,000-600,000 new cases worldwide each year, about 25,000-155,000 may be attributable to aflatoxin exposure. Most cases occur in sub-Saharan Africa, Southeast Asia, and China with largely uncontrolled aflatoxin exposure in food.

The geographical areas subject to aflatoxin growth in maize and wheat are expected to change with temperature increases – it is predicted that aflatoxin contamination and the associated food safety issues will become prevalent in Europe with a temperature increase of +2°C.

Changes in contamination patterns

Aflatoxin contamination causes significant loss for farmers, businesses, and consumers of varied susceptible crops. Climate change alters the complex communities of aflatoxin-producing fungi. This includes changes in space, time and in the quantity of aflatoxin-producers. Generally, if the temperature increases in cool or temperate climates, the respective countries may become more susceptible to aflatoxins. However, tropical countries may become too inhospitable for conventional fungal growth and mycotoxin production.

Although some regions can afford to control the environment of storage facilities to minimize post-harvest problems, this happens at high additional cost.

Many industries frequently affected by aflatoxin contamination know from experience and anecdote that fluctuations in climate impact the extent of contamination. Climate influences contamination, in part, by direct effects on the causative fungi. As climate shifts, so do the complex communities of aflatoxin-producing fungi. This includes changes in the quantity of aflatoxin-producers in the environment and alterations to fungal community structure.

Fluctuations in climate also influence predisposition of hosts to contamination by altering crop development and by affecting insects that create wounds on which aflatoxin-producers proliferate. Aflatoxin contamination is prevalent both in warm humid climates and in irrigated hot deserts. In temperate regions, contamination may be severe during drought.

Public health threat

As usual prevention is much better than late action to repair already existing damage. This is especially important in at risk regions such as parts of Africa and Asia where the risks of exposure to mycotoxins may increase under predicted climate change conditions.

The combination of future food scarcity and contamination of a larger part of the food supply has the potential of creating an explosive public health threat.

Mould on your food

artisan_bakery

What to do with artisan bread going mouldy?

You’ve bought a fancy artisan wholemeal bread made from only natural ingredients, no preservatives it proudly states. It was expensive so you only eat half of the bread, saving the rest for another day. It was wonderful. Two days later when you intend to eat the other half it is all mouldy.

In poorer circumstances there is no option but eat what is on offer. But in an affluent society we have the option to throw it out, even if it hurts as it was so nice.  Or you could attempt to rescue the unaffected part.

What to do?

Let’s look at the facts

Moulds belong to a large and taxonomically diverse range of fungal species that characteristically grow hyphae. The hyphae are generally transparent, so they appear like very fine, fluffy white threads over the surface, especially on food. We have tamed some moulds to become beneficial, others cause food spoilage, and yet others are seriously harmful to human health.

On the beneficial side, the most well-known mould product is penicillin produced by the Penicillium mould and used as an antibiotic to kill bacteria. Moulds are also essential components in the manufacturing of several food products, such as some cheeses, sausages and soy sauce.

On the harmful side, several moulds produce compounds toxic to animals and humans called mycotoxins. The worldwide contamination of food and feed with mycotoxins is a significant problem. According to the Food and Agriculture Organisation of the United Nation 25% of the world’s crop harvests are contaminated with mycotoxins. There are currently more than 400 known mycotoxins.

Where to find mycotoxins?

mouldy_fruit

Moulds can grow on many different types of food.

Mycotoxins can occur in a wide range of different foodstuffs. These include cereal-based products – such as bread, breakfast cereals, pasta, pastries, biscuits and snacks – groundnuts (peanuts), tree nuts, oilseeds, dried fruits, spices, coffee, wine, apple juice and milk. Mycotoxins are typically highly resistant to temperature and processing, so destruction during conventional food production does not occur.

The mycotoxins of most concern from a food safety perspective include the aflatoxins (B1, B2, G1, G2 and M1), ochratoxin A, patulin and toxins produced by Fusarium moulds, including fumonisins (B1, B2 and B3), trichothecenes (mainly nivalenol, deoxynivalenol, T-2 and HT-2 toxin) and zearalenone.

A threat to health

Mycotoxins can cause a variety of acute and chronic adverse health effects.

  • Aflatoxins, and in particular aflatoxin B1, are genotoxic and carcinogenic, and can cause liver cancer in humans.
  • Ochratoxin A causes a number of toxic effects in animal species. The most sensitive and notable effect is kidney damage. It may also have effects on foetal development and on the immune system.
  • Patulin has been shown to have various toxic effects and can harm the immune system and gastrointestinal tract.
  • Fumonisins have been related to oesophageal cancer in humans, and to liver and kidney toxicity in animals.
  • Trichothecenes can be acutely toxic to humans, causing sickness and diarrhoea, but at much higher levels than those typically present in food. Reported chronic effects in animals include suppression of the immune system.
  • Zearalenone is oestrogenic and has been shown to exhibit hormonal effects, such as infertility, particularly in pigs.

What to do with the mouldy food?

All of us have observed mould growth on food – be it on the piece of bread above or on a plum left sitting on the kitchen counter for an extended period of time. But you have no idea if this is a mycotoxin-producing mould harmful to health or just an annoyance spoiling the food.

There is a simple rule of thumb. For firm foods cut off the piece affected by the mould and eat the rest, while mouldy soft foods should be discarded.

Hard cheeses are good examples of firm foods that can be rescued. Moulds need moisture to grow and in dry cheeses like cheddar and parmesan there is not enough moisture for the mould to penetrate beyond the surface. Thus it is fine to remove a two centimeter piece of the cheese around the mould avoiding to cut into the mould.

Similarly, firm fruits and vegetables (such as cabbage, bell peppers and carrots) are fine to eat after removal of the mould.

And by all means remember that for some foods, like certain soft cheeses and processed meats, mould growth is part of the manufacturing process and they are perfectly fine.

On the other hand, mould on the surface of fluid foods such as yoghurt usually means that its mass of thread-like filaments have penetrated the item. Better discard the lot.

But how about our artisan bread, it is fairly dry but not really hard? This case is a little trickier. It might be sufficient to remove a solitary mould and eat the rest of the bread. However, with more extended mould growth the risk is higher. It might pay off to throw away the lot.

A final word of warning

pollution(Eric_Huybrechts)

Global warming will support further mould growth (Photo: Eric Huybrechts)

It is generally acknowledged that aflatoxins are genotoxic carcinogens. As a matter of fact they are amongst the most potent mutagenic and carcinogenic substances known.

A number of epidemiological studies have shown clear associations between aflatoxin exposure and incidence of liver cancer in areas with high prevalence of chronic hepatitis B, which is itself a risk factor for liver cancer.

Unfortunately, global warming will exacerbate the situation as mycotoxins occur more frequently in hot and humid climates favouring the growth of moulds.

The future might be bleak unless action is taken now to curb greenhouse gas emissions.