‘We have learnt that chemistry is not an exact science.’ That howler came from Mario Andrada, a spokesman for the Rio de Janeiro Olympics, who was trying to explain why the organisers had had such difficulty pinning down just why the swimming pools in the aqua centre had gone a murky green and now smelt like a week old scotch egg. As I’m sure Chemistry World’s readers would agree, chemistry is indeed an exact science – provided it is conducted under proper conditions.

When the Olympic diving pool went green speculation was quickly rife as to exactly what was going on. Theories ranged from corrosion of pipes leading to the formation of various metal oxides, excess copper sulfate or a large algal bloom. These were some of the more sensible ideas. A few more outlandish suggestions included inks running from the banners in a heavy rainstorm, chemicals added to the pool to spot crafty urinators and swimmers’ fake tan.

The Olympic organisers were clearly embarrassed by the pools’ emerald hue but seemed at a loss to explain what was happening. First, organisers blamed algae but quickly changed their mind and said it was down to a drop in the alkalinity of the pool. But then they changed their mind again and concluded that a large amount of hydrogen peroxide had accidentally been added to the pool. Hydrogen peroxide reacts with the hypochlorite added to swimming pools to kill microorganisms and quickly breaks it down in an energetic reaction giving the algae free rein to multiply. Many members of the general public have found out the hard way about this potentially violent reaction when mixing different cleaning products together.

The moral of this particular story is that to reach solid conclusions on why something has happened you need good observations. For those of us on the side lines we’ve been left making informed guesses as to what’s been going on. But the pool maintenance staff should have been able to quickly tell that hypochlorite levels had fallen precipitously, but why this didn’t happen faster is probably something we’ll never know. What’s clear is that the maintenance staff were poorly prepared for a mishap. While chemistry is an exact science it’s only as good as the people operating its tools. It leaves one wondering why there wasn’t a biologist poolside with a glass slide and a microscope…