Isn’t it safe to eat everything that grows naturally?

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Many micro-organisms and plants are very skilful in using chemical warfare agents. They produce toxins to fight off their competitors as well as using them against animals trying to eat them. Humans have also learned to utilise these toxins. As first noted by Alexander Fleming, a number of bacteria or fungi have been found to produce antibiotics capable of killing other bacteria; these include penicillins and tetracyclines. Furthermore a great number of plant toxins are in use as medicines, e.g. digitalis, curare, atropine, and morphine.


Certain fungi (microfungi) are good toxin-producers, e.g. Aspergillus, Fusarium and Penicillium. Aflatoxin B1 produced by Aspergillus flavus is a potent animal carcinogen and a probable human carcinogen.[1]

There are also many mould toxins that are toxic to the kidneys or nervous system. Dicumarol and related anticoagulant drugs preventing blood clotting were originally found in spoiled sweet clover – its consumption was found to cause haemorrhaging in cattle. Mould toxins are formed especially if there are warm and moist conditions, and these poisons are often found in peanuts, nuts, and moisture-ridden cereal.

Ergotamine used to be an important medicine in the treatment of migraine. It is extracted from Claviceps purpurea, a fungus growing in cereal grains, especially in rye, forming large black sclerotia. The fungal toxin is a potent constrictor of blood vessels. It was responsible for a number of epidemic outbreaks throughout the history. Typical symptoms have included gangrene of feet and arms, and different psychic and neurological symptoms including hallucinations and irrational behaviour. The disease was known as St. Anthony’s fire. Some investigators have even suspected that the witch-trials three or four hundred years ago were partially provoked by the weird behavioural symptoms common in ergot poisoning. Proper sifting of the grain to remove the sclerotia containing the alkaloids as well as the use of fungicides have brought this problem under control.

Bacterial toxins

Many bacteria produce toxins or other chemicals that can cause acute illnesses. The most potent of these is botulinum toxin from Clostridium botulinum. Today illnesses caused by this nerve poison are rare in industrialised countries. Botulism may be caused by poorly sterilised home-canned preserves or sausages (botulus in Latin). Since botulinum toxin can paralyse muscles for a long time, it has been used to reduce wrinkles by injecting very small doses of the toxin into the skin. Isn’t beauty dangerous!?

Several staphylococci, Clostridium perfringens, Bacillus cereus, and some other bacilli may produce toxins in food or human digestive system, and in this way cause food poisonings. There is a sad story of a food poisoning in a jumbojet somewhere over Siberia after its departure from Tokyo. Staphylococcus aureus may cause food poisoning within a couple of hours, if the bacteria present in the food have time to produce enough toxins before it is served. Now these bacteria had entered the food served during the flight, from a purulent skin lesion on the hand of the cook who prepared meals for that plane. The bacteria had ample time to multiply in the ham omelette, because the cook was so busy that he forgot to push the full cart of food into the cold store, and it stood on the counter at room temperature for 14 hours. The result was a complete catastrophe in the plane when all 196 passengers became sick with vomiting and diarrhoea within a few of hours, and queued in vain for the few toilets at an altitude of 10 kilometres. The hapless cook committed suicide, the traditional Japanese hara-kiri, after he learned of the catastrophe.

Prevention of food poisoning is based on good hygiene and proper food preparation, and adequate serving and storage temperatures and times. Bacteria may also produce so called biogenic amines which can evoke symptoms. These symptoms often start quite soon after the meal but they do not last for very long. The best known of these kinds of biogenic amines is histamine, and this is found occasionally in tuna.

Plant toxins

Most people know that some mushrooms (which in fact belong to the fungi or macrofungi rather than being plants) are poisonous, though the species vary from country to country. Perhaps one of the best known is the red toadstool Amanita muscaria, fly agaric which contains several neurotoxic alkaloids. Other members of the Amanita genus are life-threatening Amanita phalloides, death cap or deadly nightcap, and Amanita virosa, destroying angel, both of which contain the peptides phalloidin and amatoxin which are capable of killing liver cells.

Other life-threatening mushrooms are some species of the Cortinarius genus, e.g. Cortinarius rubellus (deadly webcap) and Cortinarius speciosissimus, which have caused kidney damage requiring dialysis or kidney transplants. There are interesting differences in how mushrooms are viewed in different countries. Gyromitra esculenta, false morel, is considered a poisonous mushroom in some countries, and a delicacy in others. It requires great care in its handling in the kitchen but its toxin, the liver-damaging gyromitrin, can be largely removed by thorough drying plus boiling or parboiling/blanching twice in lots of water.

There are a number of poisonous plants in the family Solanaceae (potato-family), and often even some parts of the common species contain poisonous alkaloids or glycosides, for example potato and tomato. The levels of the potato glycoalkaloids solanin and α-caconin are very low in cultivated varieties, but if the potato tubers sprout or are in sunlight and turn green, then the concentrations increase. In the Brassicaceae family (including e.g. cabbage and turnip with their many relatives) there are many species with active compounds that [2] the enzymes which are responsible for metabolising foreign chemicals and other compounds that disrupt hormonal functions.

Globally, the health effects of plant toxins often have been accentuated by poor harvest and famine. This has resulted in hurried preparations of food and making compromises in traditional ways of safe preparation. Examples are phytoagglutinins of some beans and the cyanide producing glycosides of cassava. These risks are not likely to be relevant in the developed industrialised countries.

Some risks may be expected, if as a way of avoiding the dreaded synthetic pesticides, plant cultivars are developed that contain "natural pesticides." There is no a priori reason to assume that natural pesticides would be less harmful than synthetic pesticides. There are many plant toxins that would be considered as risky, if the same criteria applied for synthetic chemicals were to be applied for these natural agents.

Natural chemicals present in food are just as risky as synthetic chemicals. The general public is less aware of these risks, and globalisation may well increase the risks associated with certain foodstuffs.

Notes and references

  1. See also the chapter "What happens when a building suffers moisture damage?"
  2. Enzyme induction means activation of enzymes by chemicals, often but not always by those that are broken down by the enzyme. This is one of the ways of the organism to be prepared to combat noxious agents that are not always present; it is more economical than having the enzymes highly active all the time.

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