Copper Turned The Olympic Pools Green, Not Algae
It’s been a week of emerald schadenfreude at the Rio Olympics. The smell of rotten eggs and those glistening green pools were truly a spectacle to behold. So were the brave athletes who swam in them — I probably wouldn’t have.
But all good things must come to an end, and so our verdant pools have been drained. That brings us to ask the question; what the heck happened? Green swimming pools aren’t a typical hallmark of the summer Olympics. We also heard reports that the whole room smelled like fart, that swimmers eyes were irritated, and blonde hair was turning green in the water. So really, what was the deal?
The official story (as we’ve been told) is that the pools were green because they were full of algae, after someone neutralized the chlorine with 160 liters of hydrogen peroxide by mistake.
That sounds plausible, and certainly embarrassing for the Rio officials, but I don’t believe it. The water was the wrong shade of green, and too clear to be algae. Also, the whole room smelled like poo gas. Algae won’t do that. I think it was copper (II) sulfate.
It’s pretty common to add both chlorine and copper (II) sulfate to pools to keep them clean and control algae. Copper (II) sulfate is purchased as a blue powder, but in pools, it combines with chlorine to form copper (II) tetrachloride, which is very green and known to irritate eyes. Normally, it’s added in very small amounts so you don’t notice the color, but if you add too much, it can turn entire pools bright green like we saw in Rio.
As a bonus, copper sulfate and chlorine also make hydrogen sulfide, which is the smell of rotten eggs and some very nasty farts. Copper (II) sulfate and hydrogen sulfide are toxic too, for those keeping score.
So how did that much copper (II) sulfate get added? Your guess is as good as mine.
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Credits
Editing: Benita Lee
Stoichiometry: Dan Mark
