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Myth: “All things are poison, only the dose determines the hazard”

Myth: “All things are poison, only the dose determines the hazard”

Photographer:Fotograaf: Joey Roberts

Myth busters

It all started in the sixteenth century, when the Swiss natural scientist and doctor Paracelcus wrote in one of his many works: ‘All things are poison, nothing is without poison, only the dose determines whether something is poisonous.’ This quote has been used since the twentieth century by toxicologists and industrialists in debates about dangerous and harmful substances, says Ernst Homburg, professor of History of Science. Whether it is about the effects of pesticides on the environment, or preservatives in our food, they continually argue that it is not the substance itself, but the dose that determines whether something is bad for humans and nature.

Homburg feels that this is a clever move, but those who consult the books, will see that the sixteenth-century scholar meant something else. The statement was made by the doctor as a defence, in a reaction to criticism by physicians about his new medicine against syphilis - a combination of arsenic, mercury and antimony - which they called poisonous. “He does not speak of smaller or larger, and hence more dangerous doses of a certain substance. He does not mention amounts, he writes about a ‘harmonic’ dose. His idea was that every substance contains good and bad, and it is up to the alchemy to separate the two. The separation process - Paracelcus believed that there is an alchemist in every body - determines whether something is good or not. The alchemist himself must try to imitate that.”

“I study the History of Science and I thought it was strange that the industry and toxicologists used a quote from the sixteenth century. Guys, you surely know that it meant something different back then. I am a chemist and an environmentalist from the nineteen-seventies and -eighties, I can see that this statement is used to take the sting out of the debate.

“Incidentally, it is a quote that was given a make-over in the twentieth century, in the three previous centuries, it lay in mothballs. It is interesting to know why it was brought into use again.” Homburg, who carried out research into Paracelsus's work, together with a German colleague, has some ideas about that: “It appears for the first time in the nineteen-thirties in Germany, in a debate about preservatives. There was a revival of the health cult, advocates of naturalism protested against the so-called mechanistic medicine, which was said to be based too much on physics and chemical laws. Paracelcus here received – neutral – attention as a believer in the balance of things. How clever of the industry to use the same quote as these nature freaks!”

Mythbusters is a series in which academics shoot down popular myths on complex topics



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