Why is green the color of poison?

May 13, 2015 , Elena Laricheva

Have you ever wondered why poison is so often associated with the color green? Take movies or video games, for example: even the vials containing poison would frequently be made of a green glass. Sure, there are poisonous plants and all, but look no further than the 18^th century, when some toxic green pigments forever ruined the reputation of the color.

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Photo by patimbeau / CC BY-NC-SA 2.0

##What were those pigments?

In the late 18th century, the Industrial Revolution was in full swing. It modernized cities, but also painted them dull gray. People craved colors as never before, and the vivacious green was in special demand. One day, a Swedish scientist Carl Wilhelm Scheele prepared a bright green compound by mixing sodium arsenite with copper sulfate and named it Scheele’s green. Together with Paris green, which is its stable acetoarsenite version, it quickly became immensely popular and widely used: green colored dresses, green decorated furniture, and green painted walls of the living rooms.

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There was one drawback though, which the rats in the Parisian sewers had quickly learned. The beloved pigments of Cézanne and Monet, who excessively used them in paintings, Scheele’s and Paris green were so toxic that they were routinely used to kill the rats. So toxic, in fact, that Monet’s blindness, Cézanne’s diabetes, and even Napoleon’s death are still blamed on them.

##And why were they so toxic?

Today, scientists know that the cause of massive poisoning was not so much the pigments as the overall exposure of people to arsenic. A byproduct of mining copper and gold, arsenic was cheap to produce and abundant. Arsenic compounds were often prescribed to treat asthma and cancer, applied to a skin to improve its complexion, added to drinks to poison rivals or accidentally mixed into food.

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Photo by Nesster / CC BY 2.0

Once, a company “Humbug Willie” poisoned 200 people by selling them peppermints produced with arsenic trioxide. Not that it was intentional — a lousy pharmacy apprentice confused the substance for a sugar substitute and sold twelve pounds of it to the company.

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Photo by Wellcome Library / CC BY 4.0

Now, consider clothes, wallpaper, curtains, and candles — all dyed with Scheele’s and Paris green — and you have a recipe for an even more poisonous disaster. The pigments were often poorly applied and would easily flake off producing toxic dust. Ingested or absorbed by the skin, they are quickly metabolized. Arsenic binds to thiol (-SH) groups of enzymes, disrupts their functions and perturbs the machinery of life. Factor in trimethylarsine, (CH₃)₃As — a toxic gas produced by the mold in wallpaper that metabolizes the pigments – and you’ll understand why people were dying like flies.

poison Reaction of arsenite with thiol groups

Indeed, it was an era when a woman could easily slay a menagerie of admirers while waltzing in her green dress, when the words “sweet poison” had literal meaning, and when the green walls could kill. No wonder poison is so often associated with the color green.

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