Swimming Pool Chemistry ... Not Pretty With a heat wave scorching the Northeast, a dip in the pool may sound like just what the doctor ordered. But before diving in, consider the chemistry. Engineer Ernest Blatchley reveals many things you didn't want to know about swimming pools and the chemical reactions occurring in them.

Swimming Pool Chemistry ... Not Pretty

Swimming Pool Chemistry ... Not Pretty

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With a heat wave scorching the Northeast, a dip in the pool may sound like just what the doctor ordered. But before diving in, consider the chemistry. Engineer Ernest Blatchley reveals many things you didn't want to know about swimming pools and the chemical reactions occurring in them.


It's hot, really hot. The temperature has topped 100 degrees. It's like a furnace outside. But there is some relief: the swimming pool just down the block, the refreshing oasis in that blacktop jungle.

So you don your swimsuit, and you ooh-ah your way across the hot pavement and jump into that chlorinated, cooling comfort. Oh, life is good - or is it? Have you considered what you're diving into?

(Soundbite of music)

FLATOW: My next guest studies the chemical reactions that occur in swimming pools, and it's worse than you thought. Ernest Blatchley is a professor of engineering at Purdue University, and he joins us by phone from West Lafayette, Indiana. Welcome to SCIENCE FRIDAY.

Professor ERNEST BLATCHLEY (Engineering, Purdue University): Well, welcome, thank you.

FLATOW: You know, we put we were having fun with the swimming pool, put a little "Jaws" music in there, but your research shows that there are chemicals in swimming pools that we should be worried about. There's like a chemical soup going on in there.

Prof. BLATCHLEY: Yes. And I think we're largely responsible for it.

FLATOW: We? You mean we as individuals going in there?

Prof. BLATCHLEY: Sure, the people who use pools.

FLATOW: Tell us about why that is.

Prof. BLATCHLEY: Well, people's, let's say, social habits have evolved such that a lot of people don't worry about perhaps using the pool as a urinal as opposed to what we might ordinarily use as a urinal or a toilet. And also, people don't remove things from their skin that perhaps they should just by taking a shower. So when those things end up in pools, they end up reacting with, among other things, chlorine to produce some interesting chemicals.

FLATOW: What kinds of chemicals are we talking about?

Prof. BLATCHLEY: Well, there's a group of chemicals called the chloramines that are generated by pretty much any chemical in water that contains nitrogen. That's a bit of a generalization. But there are some other disinfection byproducts that are generated, for example, cyanogen chloride, dichloroacetonitrile, the halo forms. These are things that show up in drinking water as a result of very similar reactions. But not surprisingly, they end up in swimming pools as well.

FLATOW: And is it because of the chlorination in the pool?

Prof. BLATCHLEY: Yes. You could say that. I think without chlorine these chemicals wouldn't be generated.

FLATOW: Mm-hmm. Is there something, a sickness that we might not suspect we have but, you know, can affect us if we're in a swimming pool?

Prof. BLATCHLEY: Well, there are - there have been - first of all, the CDC has developed a division that looks into what they refer to as recreational water illnesses. They - so they developed that term, recreational water illness, to describe these things. And these are conditions that are attributable to exposure to microorganisms or chemicals in pools or sometimes combinations of these things. And they range from, you know, skin rashes to eye and skin irritation, to respiratory problems. And there have been suggestions, although they haven't necessarily been proven, that there is possibly a link between some of these chemicals and the promotion of asthma in some people.

FLATOW: Hmm. And so, there are microbial diseases in the water also?

Prof. BLATCHLEY: Sure. Microorganisms like warm water so - and sometimes we leave them behind for various reasons.

FLATOW: And so, when they say to you, and you see this at the pool all the time, take a shower before you come in here, they really mean it?

Prof. BLATCHLEY: I think it's a good idea. I think, yes, they do really mean it. I don't know that they always understand why. But we're hoping to take some of the work that we've done in the lab and in swimming pools and translate it so that the public can understand why it's important to do this.

I think most people take it for granted that, you know, swimming pools are going to be clean. And that, you know, if they jump in without taking a shower, it probably won't make any difference.

FLATOW: Mm-hmm. Talking about swimming pool hygiene this hour on SCIENCE FRIDAY from NPR. I'm Ira Flatow talking with Ernest Chip Blatchley.

So what do you say to somebody who wants to, you know, go to the swimming pool? Should they be fearful of getting some sort of illness from the pool?

Prof. BLATCHLEY: I'm glad you brought that up. I mean, in a general sense, I think, no, they should not. I think most pools most of the time are really pretty clean and the benefits associated with swimming in most circumstances, you know, outweigh the risks. But I think people can do some just basic things that could improve swimming pool chemistry and air chemistry, especially in indoor swimming pools, that would benefit not only themselves but the other people who use the pool and the people who work in those pools.

FLATOW: Mm-hmm. Such as?

Prof. BLATCHLEY: Well, taking a shower is a good idea. I mean, it really does make a difference in terms of removing some of the chemicals from your skin that ordinarily would be just removed when you dive in...

FLATOW: Right.

Prof. BLATCHLEY: ...or jump in. And, you know, a really important one, although it may surprise a lot of people, maybe it won't surprise a lot of people, is that, you know, people should urinate not in the pool. Use the bathroom. There's a remarkable amount of urine that ends up in pools, most of it voluntarily, let's say, introduced...


Prof. BLATCHLEY: ...because nobody is going to know.

FLATOW: A lot of people with baby diapers, too.

Prof. BLATCHLEY: Yeah. There's not much you can do about that. And, you know, even if people displayed what I would consider to be ideal hygiene practices in swimming pools, there's still going to be some of these compounds that are going to end up in pools. But we could do a much better job of limiting the amount of these chemicals that go into pools.

FLATOW: Of course, if some of these chemicals, the soup, the result of what's going on in the pool gets sprayed up into the air, you breathe that stuff in too, I would imagine.

Prof. BLATCHLEY: Sure. So swimming, I mean, is kind of an interesting, let's say, pathway for exposure to chemicals that are in water because, you know, when go swimming, you're, first of all, you're immersed in the water, but you're also probably breathing air right above the air-water interface.

FLATOW: Mm-hmm.

Prof. BLATHLEY: And probably you're going to ingest some water while you're there. So there's opportunities for exposure from at least three different pathways. And the one that you mentioned about, you know, release to gas phase, is particularly important with respect to the respiratory ailments that have been linked one way or another to swimming, especially in indoor swimming pools.

FLATOW: Let me get a quick call from Melissa(ph) in Denver. Hi, Melissa.

MELISSA (Caller): Hi. Thanks for taking my call. A freaky topic. Two questions for your guest. One, I - in my condo complex where I live, they switched over from the chlorine-based chemicals to clean the pool to a saltwater system. And my first question was, is that any better or is it any worse?

Prof. BLATCHLEY: It's hard to say at this point. It's not really a lot different because what they're doing there is they're generating the chlorine by a process called electrolysis. So they've added the salt to the pool and then they re-circulate that water through an electrolytic cell and they generate the chlorine that way. So, really, a lot of the same chemistry is going to be taking place. It's a little bit different just because of the salt that's present in the pool, but not a lot.

FLATOW: But what if you had a saltwater pool instead of freshwater?

Prof. BLATCHLEY: Well, I think that's actually what she's referring to.

FLATOW: That's what that is.


FLATOW: So no one is just getting seawater being pumped into their swimming pool.

Prof. BLATCHLEY: Not that I'm aware of, but I haven't done a complete survey so I don't know that so...

(Soundbite of laughter)

FLATOW: Someone writes: Does potassium peroxide monomer sulfate fix what's going on in there?

Prof. BLATCHLEY: So there are peroxide chemicals that are used in addition to chlorine, and that's usually how they're added. And I'm not sure, honestly, how much difference there is between a pool that uses chlorine alone and a pool that uses chlorine plus a peroxide chemical. So I don't really know the gory details of how the chemistry plays out under those.

FLATOW: All right. We won't - and we won't ask you to talk about something you don't know about. But I want to thank you for taking time to be with us today.

Prof. BLATCHLEY: You're welcome.

FLATOW: Ernest Blatchley, professor for engineering at Purdue. He joined us from West Lafayette, Indiana.

We're going to take a break. Come back. We're going to talk about, well, stuff that's lurking in the garden. Forget the pool. We're now moving to the garden. And, oh, my pesto preparation is in trouble so maybe yours is too. Stay with us. We'll tell you why after this break.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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