That chlorine smell at the pool? It’s pee
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Hey, it's Flora, and you're listening to Science Friday. On a hot summer day, there is nothing better than a dip in a cold pool. But you know who can ruin that for you? A scientist who studies pool chemistry. What chemical reactions are happening in that swimming pool? My next guest has researched this for decades, including at the Paris Olympics pool, and is here to share his findings. Dr. Ernest Blatchley is a professor of environmental engineering at Purdue University. Welcome to Science Friday. Thanks for being here.
Thank you for the invitation.
Is it fair to say that a swimming pool is an active chemistry experiment?
It's really a reactor. People jump in the pool and they leave various things behind that might have been on their skin, including sweat, deodorants, things that they apply to their skin like makeup or sunscreen. There's also chlorine in the pool and people urinate or pee in the pool more often than you would think.
What do you mean more often than I would think? Have you quantified this?
I have not personally, but I think if you were to do a survey, I have done this sort of informally. If you were to do a survey of people who swim in a pool, first of all, ask them to close their eyes so that they can't see the responses of other people in the room. But ask them how many people pee in the pool. You'd see, I don't know, three quarters of the people in the room are going to raise their hand.
Are you surveying adults?
Yes.
Okay. I don't know that I want to know this. Okay. So keep going.
Well, if you were to talk to competitive swimmers, for example, they commonly will not get out of the pool. And yet all of them, or virtually all of them, have one or two water bottles waiting for them at the end of the lane when they're resting between sets. Do the math. So it's just the way it goes.
Okay. So I'm hearing that there's lots of different ingredients. Why is it a reactor? What happens with those things we leave behind and the chlorine?
Well, so we use chlorine in pools to inactivate microbial pathogens that could cause other problems. And chlorine is pretty good at that. But chlorine also reacts broadly. It's a very reactive chemical, and it's going to react with many things that are present in pools.
How does urine affect pool chemistry and the chlorine smell?
And among those, let's just say, human body fluids that I described a few minutes ago, there's a lot of compounds that contain organic nitrogen. And it happens that organic nitrogen in particular reacts very rapidly with chlorine and And some of the products of those reactions are unpleasant and have potentially adverse human health effects.
Give me an example.
Perhaps the sentinel compound among the various compounds that we and others have identified is a chemical called trichloramine. You're probably familiar with this chemical, at least by its smell. So if you're ever around an indoor swimming pool, especially one that's not operated particularly well, there's oftentimes this sort of chlorine odor that most people will recognize. That is, in fact, largely attributable to trichloramine.
I'm not smelling the chlorine. I'm smelling trichloramine.
You're smelling a product of chlorination. Exactly. Exactly. So that chemical is interesting because it's volatile, which means it has the ability to escape from the liquid phase to the gas phase. So it's going to end up in the air that we breathe. It is a chemical that's known to cause problems for the human respiratory system, and it also causes things like corrosion. So if you look around in an indoor pool, oftentimes you'll see stainless steel that is, well, stained. It's been corroded, and much of that corrosion is attributable to trichloramine. So think about a chemical that has the ability to corrode stainless steel. probably not going to do nice things to your lungs either.
What about your skin? Do we have to worry about it on our skin?
Yeah, there are some people whose skin is irritated by chloramines broadly, including trichloramine. But that it's a pretty, I don't honestly know the sort of medical explanation for this, but that's pretty variable among people.
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