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Cool Science: Smells like skunk season

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Cool Science: Smells like skunk season

We are all very familiar with the smell left behind after a skunk has sprayed its odiferous scent. The science behind skunk smell is very interesting; from the striped skunk’s natural history to the chemical make-up of this foul-smelling defense mechanism.

The striped skunk (Mephitis mephitis) is distinctive because of the bold markings that run down the length of its body. This type of colouration is a great example of aposematism; a warning signal for potential predators. For most predators, this signal is warning enough. For others who perhaps have not encountered a skunk in the past, may continue to bother the striped mammal. When mortally threatened, they bend into a U-shape with both their head and rump facing the enemy. They then emit two streams of fluid from scent glands located just inside the anus, which turn into a fine spray that can travel up to 2 or 3 metres. The spray often burns the eyes and nasal cavities and can cause nausea. It is because of their offensive odour that skunks are rarely preyed upon by other mammals, but instead are eaten by large predatory birds like owls and hawks.

Contained within that stinky scent is a combination of chemicals, mostly sulfur-containing compounds called thiols and thioacetates. Not surprisingly, thiols are also found in other smelly materials, like rotting flesh and feces. The skunk spray itself is in the form of oil which will cling to most surfaces that it contacts. If that surface happens to be an unfortunate pet, the thiols will bind strongly and rapidly to skin proteins. This scent will stick around until the thiols break down naturally, which could take several weeks. And if the animal becomes wet, the smell is even more pungent because the thioacetate is readily converted to the smellier thiol when mixed with water.

In order to neutralize the odour both the chemical structure of the volatile compounds and the oil need to be broken down. Unfortunately, tomato juice just does not work to do this; it just makes a big mess! A simple home remedy is to mix hydrogen peroxide (3%) with baking soda and add a little dish detergent. Hydrogen peroxide and baking soda act as oxidizing agents, changing the chemical structure of the thiols into odourless sulfonic acid compounds. The dish detergent helps to cut the oil so that the by-products of the initial chemical reaction can be washed away. The most common combination of these ingredients is 3-4 parts hydrogen peroxide, 1 part baking soda and a teaspoon of dish detergent. To be most effective, this solution must be used immediately after mixing while it is still bubbling and should be applied directly to the affected areas.

In the video, I use a more concentrated hydrogen peroxide (30%) to show how reactive it is. This chemical reaction is often referred to as “elephant’s toothpaste” because the resulting foam looks like toothpaste big enough for an elephant! I mix hydrogen peroxide with dish soap and then add sodium iodide, a catalyst that drives the reaction. You can try this reaction at home with some household ingredients. The reaction won’t happen as quickly as the one in the video but it will still be impressive. Measure out 100 mL of hydrogen peroxide (3%), add ½ teaspoon of dish soap and then add 1 teaspoon of bread yeast. Try varying the amounts of materials to see if the reaction changes!

Now that’s cool science!

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