12 September 2019 0 By Sco

On the contrary to artificial food contaminants like pesticides, the toxins of molds are neglected by the public and their impact on health is often underestimated.

This is an english adaption of my recent article in german.

You wouldn’t eat that bread, right? Well that’s because you’re not my roommate from student days… Pic from Henry Mühlpfordt , published on Wiki, CC-BY-SA 3.0


Everybody seems to be afraid of chemistry in foods these days. Pesticides, plasticizers, artificial colourings and flavourings share a bad reputation – and in some cases, of course, quite rightly so. Organic food is the trend, the food industry is out and even the most unhealthy sweets are now coloured with vegetable dyes.

A very old phrase, however, is often ignored by health-conscious superfood disciples:

Everything is chemistry!

Whether a substance enters food by a natural or artificial way is completely irrelevant from a toxicological point of view. Nature has a repertoire of dangerous toxins that can sometimes be found in food.

However, due to public pressure, the tougher regulations regarding legal limit values and necessary controls undoubtedly apply to industrial contaminants and additives. In addition, there is much more scientific data on these chemicals, as there are lobbies on both sides who actively conduct research.

This leads to the slightly paradox situation that artificial food contaminants are widely discussed in public even if the effect on human health is so small that it can only be proven in special cases while natural problem substances are largely ignored by journalists. Who hasn’t heard of glyphosate yet?
But does anyone of you know Aflatoxin B1? You should , and it’s my duty to close this gap of knowledge.

Under these conditions it should not surprise the educated laymen among you that I, as a toxicologist, consider the natural toxins to be the greater danger.

It still surprises you, I know. But I will explain it to you. Spotlights on, I  present you the mold toxins, also known as mycotoxins.

But before we begin, let me warn you: If you want to continue cooking with canned tomatoes or eating pistachios without hesitation, don’t read any further. I have already spoiled the appetite of some of my acquaintances, and I will do it again.

Occurence and original function

Moulds, and everyone who ever forgot about food a fridge knows this, occur “ubiquitously“. This means that they grow under almost any conditions (e.g. in the refrigerator), are spread all over the world and their spores are almost everywhere. When they grow, many of them produce toxins. These are not primarily directed against humans – we are not a natural enemy of mould (some, like my former roommate mentioned above, are even natural allies). No, mycotoxins essentially have two biological functions:

Firstly, to combat everything that competes for nutrients, which means other microbes, especially bacteria. Therefore, traditional antibiotics such as penicillin also belong to the substance class of mycotoxins.

And secondly, the toxins are supposed to damage the plant tissue in order to make it easier for the fungus to penetrate its host.

As a side effect, however, many of these substances are also toxic to higher organisms, in a variety of ways that might differ from toxin to toxin.

Human exposure

… but processed foods are consumed without a second thought. Pic from Pixabay , CC0

“Fine and good, dear Sco,” I hear you saying, “maybe it concerns others, but for my part I always throw away mouldy food right away!”

That’s good and right. But who said that mould must develop in your place?
This is the reality of today’s food production: Two million tomatoes are mashed up in a fat factory and packed in cans. Do you really think they are all individually and manually examined for small black spots? One can safely assume that the Polpa is contaminated to a certain degree. Actually, we don’t have to assume, we know it.Ref The study of an esteemed colleague of mine was quite clear about that.

Of course, the tomato sauce is sterilized before shipping. This kills the fungus itself, but the chemicals it had already produced at that time are relatively indifferent to heat or UV radiation.

In the pizzeria around the corner, the good sauce is then used on your Pizza Capricciosa, and 20 bites later the mycotoxins end up in your intestines.

The tomato sauce was of course just an example, you can use any other processed vegetables and fruits instead. How many of you eat things whose raw materials you had in your hands for optical evaluation of quality?
Now you get my point.

The problem with regulations

“But there are certainly legal limits that must be observed?”

Yes of course. Eight particularly dangerous mould toxins are regulated in the EU, namely the aflatoxins B1 and M, ochratoxin A, zearalenone, a-zearalenol, deoxynivalenone, patulin and citrinine. Ref1, Ref2

Eight. Of currently over 400 known substances produced by moulds. About which there is for the most part no sufficient data to know whether and how they affect humans.

Thus, the majority of toxins are not even searched for in food (the industry only performs analyses to which they are obliged), hence the Alternaria toxins in tomatoes. And it is certainly not the case that Alternaria toxins are harmless in any case. Some of them are genotoxic in human cells and therefore potentially carcinogenic. Others activate hormone receptors and are therefore suspected of disturbing our hormonal balance. And I don’t even get started on the problem of chemical mixtures (you don’t eat a single mycotoxin, but due to multi-contaminations 100 different ones at the same time, with interactions, cumulative effects etc.).

Late-stage Alternaria growing on (and in) tomatoes. Pic by Scott Nelson, public domain.

But research is just not advanced enough to enforce regulation. And there is a simple reason for this: there is almost no economic interest in toxicology. On the contrary, new limits would cost agriculture and industry money. In contrast to our sister discipline, pharmacy, we therefore have to finance ourselves mainly from public funds, which are rather sparse for obvious reasons – after all, it’s taxpayers’ money. Accordingly, our research is underfinanced and slow compared to other disciplines.

But even in the case of substances for which limit values already exist, there are troubles. Take aflatoxins, for example. I have already written an article about them quite some time ago. In short, aflatoxins are produced by fungi that prefer to grow on nuts and legumes at tropical temperatures. Pistachios are particularly susceptible to this.

The problem is that aflatoxins are extremely potent carcinogens. Relatively small amounts of AfB1 cause liver tumors quite reliably. And if a single pistachio is affected, it is often affected in very strongly, with big doses of toxins formed. If you’re unlucky, one nut is enough.
This leads to the situation that the limits, which are actually well set, are very difficult to monitor. A whole batch of pistachios can be completely ok, and AfB1 is not detectable in the samples drawn. But the liver of one consumer, who eats the rotten nut lying in the bottom left corner of the box below millions of others, may still be damaged.

Now what?

You can’t avoid mycotoxins to 100%, but that’s not even necessary, because we are quite well prepared for a certain amount of them through co-evolution. But it doesn’t hurt to develop a certain awareness of the problem. With a few exceptions, mouldy foods belong into the garbage, especially if they are partially liquid (tomatoes) or have air holes (bread) – which enables the fungus to spread rapidly, and with it the toxins, too.

Anyone who does without processed food and cooks as freshly as possible with manual quality control is certainly better off. And please, if a pistachio looks “funny”, don’t taste it. When it comes to exotic nuts, toxicologists are paranoid (with good reason).

Otherwise, it’s the producers in particular who are responsible: mould can usually be avoided by good storage conditions. This works quite well in Western nations, poorer (especially African) states and the wild East still have some catching up to do.

Stricter limits and a little more money for our research would not be bad either, but you have no influence on that. 😉

What you can expect from this blog…

I’m sure you’ve noticed that this was just an introduction to the subject. In the coming weeks I want to introduce you to various mycotoxin groups, their occurrence and effects, and we will certainly go a little deeper into molecular biology.

Until then, cya soon!


In my blog, I’m writing my honest opinion as a researcher in toxicology, not more and not less. I am human, I make errors. Discuss and disagree with me, if you’re bringging the better arguments, I might rethink.


Finding sources in your own field, where you just write the text from memory, is always a bit special. 😉 I quoted some of them in the text, if you want further information, you can read it here: