This summer, when I tuned in to the Rio de Janeiro Olympic games and saw cloudy green waters in the diving pools, I barely batted an eye. I thought this was merely a media stunt. The Brazilian authorities had harmlessly dyed the waters green because it fit with the country’s theme. They have a green flag, they have incredible natural greenery and so on. I soon learned that this was no dye. The waters had, seemingly spontaneously, turned green overnight.
The games’ organizers pointed the finger at an unnamed stadium worker who apparently poured copious amounts of hydrogen peroxide into the pool. Possibly this was an attempt to “super-sterilize” the pool, akin to using peroxide on a skinned knee? However, like most swimming pools, this one had already been treated with chlorine. More specifically, sodium hypochlorite (NaOCl). When NaOCl is combined with water it forms hypochlorous acid, a potent antimicrobial agent. Adding hydrogen peroxide to the mix would have reacted with the chlorine-containing NaOCl in the pool, producing NaCl, O2 and water. As NaOCl is added to kill microbes such as algae, its absence allowed them to proliferate and fill the pool.
source: BBC sports
According to a recent article in the C&En News, this response has been refuted by chemists and biologists alike. It seems impossible (or, in science terms: highly improbable) that the algae could reproduce so quickly to muddy the pool overnight. Some scientists believe it was a chemical reaction resulting from the addition of copper-containing antiseptic chemicals in improper quantities. In the presence of chlorine, copper forms a green complex. This theory even accounts for the smell reported by athletes: hydrogen sulfide, which is a by-product of this reaction.
Which solution is THE solution? Image Courtesy: Leiem, Wikimedia Commons
As the Newscripts article reports, we will never know the true solution to this chemistry mystery. All pool water, and potential analytic samples, has long gone down the drain. Nevertheless, chemists will always remember the time when their discipline had its moment in the hot Brazilian sun.
– Megan Wolf
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