To Swim or Not To Swim

May 30, 2009 3:16 PM

i like to swim, but friends have been lecturing me about the dangers of chlorine -- that it's been linked to cancer, that it's god-awful for your health and well-being, even if not cancerous. does anyone have an informed opinion on this issue?
posted by LittlePumpkin to health & fitness (36 comments total)

Your friends are full of crap.

If chlorine causes cancer we'd all have been dead long since. Chlorine is half of table salt. You consume grams of it per week and have your whole life.
posted by Chocolate Pickle at 3:27 PM on May 30

Chlorine gas will kill you quickly. Swimming in normally chlorinated water is harmless.
posted by Inspector.Gadget at 3:30 PM on May 30 [2 favorites has favorites]

Just anecdotally, as a kid I spent every summer, all summer, in the pool. I am still alive and healthy.

The only thing I did notice was that all my blonde friends had green hair all summer, but that's about it.
posted by OolooKitty at 3:32 PM on May 30

i have never heard of any such thing. i have worked in the pool industry, i know many people who have pools, including doctors.

i think, in this case, the burden of proof is on your friends. the general accepted position is that chlorine in pools are safe. anyone suggesting otherwise needs to produce sufficient evidence to overcome the presumption of safety
posted by Flood at 3:32 PM on May 30 [1 favorite has favorites]

even if it was a little bit dangerous i would think you would be making up for it with the health benefits of the exercise.
posted by katieanne at 3:38 PM on May 30

Here's the MSDS for chlorine gas. Note section 11:

"Not Classifiable as a Human Carcinogen"

In high concentrations chlorine is quite deadly, but the primary means of toxicity is conversion to hydrochloric acid in presence of water, leading to burns. The main risk is inhalation, leading to lung damage.

But that's at concentrations WAAAAAAY higher than anything you'll be exposed to in a swimming pool. In which they don't use chlorine gas anyway.

What they use is hypochlorite, otherwise known as "bleach". Its active sterilization effect is to break down into a chloride ion and an oxygen radical. The radical attacks bacteria, and the chloride ion goes into solution -- and it is EXACTLY the same chloride ion as you'd get if you dissolved table salt in the water.

Here's the MSDS for sodium hypochlorite. Note section VII:

"This material is not considered to be a carcinogen by the National Toxicology Program, the International Agency for Research of Cancer, or the Occupational Safety and Health Administration."
posted by Chocolate Pickle at 3:38 PM on May 30 [4 favorites has favorites]

there are some recent studies that are showing a link between indoor swimming pools and development of asthma in children - but that is not really what you are talking about.
posted by dripped at 3:41 PM on May 30

Drinking straight chlorine is bad. But you'd have to guzzle gallons of pool water to have serious implications on the level scientifically tested for, so you're good to go as long as you're not putting pool cleaner right in your eyes.
posted by StrikeTheViol at 3:43 PM on May 30

Your tap water has chlorine in it too.
posted by b1tr0t at 3:46 PM on May 30

And since most water systems deliver chlorinated water, and have for generations, I'm sure i'd be dead by now if chlorine were deadly. I use chlorine to keep my pool healthy, and have to add it often since the sun and heat cause it to dissipate. Otherwise, the green and mustard yellow algae would take over, and bacteria would grow. Swimmers are problematic for pools than well kept pools are for swimmers.
posted by path at 3:48 PM on May 30

I'm sure your friends mean well, but they need to do some research. Herein lies the dangers of relying on anecdotal evidence. If you can't shake the fear of chlorine instilled by your friends, keep your swimming to lakes and oceans. Oh, wait, those are filled with toxins and carcinogens as well. When it comes down to it, life is "pick your poison", because no matter what, SOMETHING is going to kill you, eventually.
posted by zerokey at 4:08 PM on May 30

Chlorinated water in water systems used to be based on chlorine gas, but now most water systems use chloramine.
posted by Chocolate Pickle at 4:15 PM on May 30

If there was anything to it, we'd see elevated incidents of cancer and other health problems among professional and Olympic swimmers, who are in the pool multiples of times more than an even regular swimmers.
posted by The Deej at 4:17 PM on May 30

Agreed that chlorine dissolved at the low concentrations in tap water and swimming pools is relatively harmless.

But, regarding this:

Your friends are full of crap. If chlorine causes cancer we'd all have been dead long since. Chlorine is half of table salt. You consume grams of it per week and have your whole life.

Table salt does not contain any chlorine. Table salt is (mostly) crystalized sodium chloride. Molecular chlorine is reactive and toxic. How this affects you is dependent on concentration. Chloride ions (the "half" of sodium chloride you attempted to refer to) are inert.
posted by randomstriker at 4:42 PM on May 30 [3 favorites has favorites]

I've read studies that stated that when chlorine destroys organic material (I guess bacteria and stuff like that), it produces hazardous compounds (trihalomethanes) which are, among other things, cancinogenic. This may be what your friends are referring to. I'm not a doctor or a scientist, but I'd say the danger is pretty low for healthy individuals. If you're worried, just avoid drinking from the pool (yuck).

I'm sorry I can't provide references because I'm about to leave the house, but you can find these studies by googling "trihalomethanes". I think one of the studies was done by the Orgegon Department of Human Services. The EPA also has information on this.
posted by blisterpack at 4:49 PM on May 30 [1 favorite has favorites]

That's "Oregon" not "Orgegon".
posted by blisterpack at 4:50 PM on May 30

thanks for the answers - there certainly ARE studies that suggest a link between swimming-pool chlorine and a greater risk for cancer/other negative health effects - what i'm hoping for is an informed or even expert take on whether the studies might be poorly conducted, contain a very small sample sized, or what have you - something that would mitigate the result - like everyone else on here, i don't WANT swimming in a pool to be bad for me, and don't mean to be alarmist - but i also don't want to assume that "because we've been doing it forever it must be safe..."
posted by LittlePumpkin at 5:12 PM on May 30

When mark spitz, summer sanders, michael phelps, and natalie coughlin start getting cancer...start worrying. Until then your friends ARE full of crap...and lazy.
posted by hal_c_on at 5:32 PM on May 30

LittlePumpkinPoster: "there certainly ARE studies that suggest a link between swimming-pool chlorine and a greater risk for cancer/other negative health effects "

Which studies, specifically, are you thinking of? That would be helpful if you want people to debunk or confirm them.
posted by The corpse in the library at 5:33 PM on May 30

blisterpack: I've read studies that stated that when chlorine destroys organic material (I guess bacteria and stuff like that), it produces hazardous compounds (trihalomethanes) which are, among other things, cancinogenic.

Wiki that says pretty much the same thing. It sounds to me like if you aren't drinking the pool water, there is no real risk, and if you aren't a child there is even less risk.

It isn't a definitive answer, but there are three relatively serious looking cites, just for those two paragraphs. Personally, swimming in a puddle of bleach grosses me out, but I'm squeamish sometimes.
posted by paisley henosis at 6:12 PM on May 30

here's one:

http://www.ncbi.nlm.nih.gov/pubmed/18595407

there are some here too, but also a bunch of "quotes" without much support:

http://curezone.com/art/read.asp?ID=21&db=3&C0=7
posted by LittlePumpkin at 6:35 PM on May 30

The UC Berkeley Wellness Newsletter has research reviews online and they did mention in one of their issues a review of chlorinated water studies, so you could do a dedicated search there.

Or Medline Plus, the NIH website, you can do a dedicated search there and find a wealth of the latest clinical reviews on almost any medical topic.

Happy hunting.
posted by effluvia at 6:41 PM on May 30

here's one: http://www.ncbi.nlm.nih.gov/pubmed/18595407

Um....that link goes to a published report about the increased cancer risk from trihalomethanes, not Chlorine; it also concentrates on results in a very specific area of China. That link doesn't have anything to do with chlorine being a risk element itself, only in how the chlorine is affecting the trihalomethanes.

there are some here too, but also a bunch of "quotes" without much support: http://curezone.com/art/read.asp?ID=21&db=3&C0=7

That appears to be an alternative-medicine public forum. Not that there is no truth whatsoever to alternative medicine, but judging from the rest of the forum, it looks like the person who wrote that second article may have An Agenda.

In short, the first link is about something different and the second link is by someone with a bias. Neither count as "proof" that chlorine in pools cause cancer.
posted by EmpressCallipygos at 7:12 PM on May 30 [3 favorites has favorites]

I learned to swim before I learned to walk. I spent 90% of the summer in the pool throughout childhood. I swam competitively for seven years. When I have pool access, I still swim at least once a week.

I have never, not ever, had any doctor express any concern for my health for any reason other than swimming without a lifeguard or a buddy can be a safety hazard for me personally (I have epilepsy). I worry more about swimming in the ocean and developing skin cancer from sun exposure (many, many a time I have burned despite putting on sunscreen) than I do about any form of carcinogens that may be lurking in a pool.

Next time you go in for a routine visit, just ask your doctor what they think the risk is for chlorine. They'll probably be able to give you an opinion of whether or not this is just hype or if the health benefits of swimming outweigh the risk of possible carcinogen exposure.
posted by grapefruitmoon at 8:09 PM on May 30

A decent Google search for the asthma bit might start with: chlorine pool asthma site:gov. I'm willing to buy a mild asthma link (the swim team people I knew seemed to have an awful lot of it, made me wonder ever since) and some obvious skin irritation.

As to cancer, there's probably more skin cancer generated by people swimming outside, in the icky icky sun. That would have to be factored out of any study.
posted by adipocere at 8:22 PM on May 30

Your friends are full of crap.

for the nth time
posted by caddis at 8:58 PM on May 30 [1 favorite has favorites]

Not that there is no truth whatsoever to alternative medicine

No need to back off. Idiots are idiots, and the sooner they are exposed as such, the more benefit will accrue to public health. For future reference, OP, the minute you see "alternative medicine" start demanding the results of double-blind clinical trials. You're right to question the unattributed quotes, but be skeptical also of the "evidence" anyone presents to back up spurious, unscientific ideas.
posted by Inspector.Gadget at 9:05 PM on May 30 [1 favorite has favorites]

I'm willing to buy a mild asthma link (the swim team people I knew seemed to have an awful lot of it, made me wonder ever since) and some obvious skin irritation.

Yes, my ex-girlfriend had chlorine induced asthma. She only had asthma attacks related to pool exposure. Easy enough, her doctors advised her to stay out of the pool. This was a specific case related to an underlying condition though and not any long-term risk from the chlorine itself.

A lot of asthmatics also have asthma induced by running, FWIW. If you haven't had an asthma attack from the pool and don't have underlying asthma, you're not at all likely to suddenly develop respiratory problems from chlorine.
posted by grapefruitmoon at 9:06 PM on May 30

Nth-ing the "friends full of crap"...my mother swam every day for more than twelve years...if it did anything bad for you at all, it sure as heck would have happened to her (which it didn't).
posted by james.nvc at 9:07 PM on May 30

Chlorinated water (which contains chemicals) is safer to swim in than non-chlorinated water (which grows pathogens). That's why people chlorinate.

If your friends are suggesting you should go swimming in the creek instead of the pool, go for it. Creeks are great. If your friends are suggesting you shouldn't swim at all, thwack them.

warning: getting thwacked is bad for your health and well-being
posted by fantabulous timewaster at 9:40 PM on May 30

thanks for the answers - there certainly ARE studies that suggest a link between swimming-pool chlorine and a greater risk for cancer/other negative health effects - what i'm hoping for is an informed or even expert take on whether the studies might be poorly conducted, contain a very small sample sized, or what have you - something that would mitigate the result - like everyone else on here, i don't WANT swimming in a pool to be bad for me, and don't mean to be alarmist - but i also don't want to assume that "because we've been doing it forever it must be safe..."

Seriously? Seriously?

Sure, covalent chlorine is a problem. But, ionic chlorine is FOUND IN FUCKING TABLE SALT. Pour some table salt into a glass so that it dissolves. You have now created exactly the same chloride ions that might be found in a pool. The ocean is, you know, full of salt... which has all dissociated.

Oh, wait, this just in... if previous in-thread info is correct, and hypochlorite is what's used as pool chlorine... well, then you're not really worried about chlorine. You're worried about the hypochlorite ion (which is polyatomic). I certainly hope you don't wash your clothes with bleach. Or any bleach alternative, which have very similar chemistry.

Why aren't you worried about the oxygen in the hypochlorite ion? Oh, that's right... you think oxygen is a harmless gas, good for you even. So, of course, you'd never believe me if I talked about oxygen toxicity, or about oxygen free radicals. Did you know that ozone, which will painfully kill you in nearly the same way as chlorine gas, is just oxygen? It's O₃ instead of O₂, but it's still oxygen, right? Hell, one can commit suicide with just a tank of regular ol' medical grade, pure, breathable O₂ if you push the percentage (technically partial pressure) of O₂ just a few percent above Earth normal.

The names of the elements involved is irrelevant. The actual compound is what's key. So is the application. Buying into a blanket claim of "chlorine is bad" is about as insightful as buying into a blanket claim that "circles are bad". Well, chlorine is bad as a gas when you inhale it into your wet lungs (not a problem if we weren't so much water), but it's quite necessary for making my french fries tasty.

Furthermore, as to your actual question of whether pool bleach is going to hurt you: of course it is. Everything hurts us. But, I can guaran-damn-tee you that the pool chlorine is hurting you far less than the sun does on a daily basis--did you put on sunscreen before you drove your car (with glass windows) to the store. Far less than the smog does. Far less than your lunch did--and I don't give a shit what you ate or how free its range was.

In addition, you haven't actually shown any studies that link pool chlorination to cancer. What you have provided is a study that links trihalomethanes to cancer. Since trihalomethanes are already well-known carcinogens, the study is about as original as one saying "guns are linked to shootings". The only interesting part of the study was that some swimming pools have surprisingly high concentrations of trihalomethanes. These aren't added to the water; they're either forming spontaneously, or there's some other unexplored common factor (contaminated treatment chemicals, bad equipment, etc.). My guess is, given that the only study you've provided took place in China, that the water quality of the sample locations was particularly poor. So, I can't say that I'm at all surprised that swimmers in China get more cancer. But, I'd also be very surprised if many of these same swimmers didn't also swim in the ocean and the rivers... exposing themselves to all sorts of shit that isn't in the reporting.

If you really want to put your mind at ease, go take a couple of chemistry courses. Like, two of them. Chem I and Chem II are sufficient to keep you from ever worrying again about this sort of (to the educated at least) blatantly ignorant bullshit. It'll also help you to spot the things that really are dangerous and cummulatively harmful...
posted by Netzapper at 2:15 AM on May 31 [1 favorite has favorites]

>Not that there is no truth whatsoever to alternative medicine

No need to back off. Idiots are idiots, and the sooner they are exposed as such, the more benefit will accrue to public health.

I only say that because there is alternative medicine and there is alternative medicine. To some, chiropractics is an alternative medicine. I said what I said just to differentiate between "my chiropractor actually helped my bad back when my GP couldn't" and "this 100% ionized vitamin pill will cure my malaria."
posted by EmpressCallipygos at 5:06 AM on May 31

Athsmatic here - I get it from allergies, exercise, whatever. The second i step into a chlorinated pool i get at least a mild attack. Always take my inhaler as i know it's coming now.

Cancer no, but it's definitely something to be aware of, if you have a vulnerable respiratory system or something, from my experience anyhow.
posted by greenish at 7:45 AM on May 31

I suspect the health benefits of swimming far outweigh any problems with chlorine. Chlorine has been used for a long time. If the health benefits were dire, it would be documented by now.
posted by theora55 at 9:01 AM on May 31 [1 favorite has favorites]

I used to swim almost daily in my teens and twenties, no physical effects except my eyes, which would burn like hell for hours if I didn't use goggles. This wasn't restricted to my most common pool either. I never swim without goggles in a pool now.
posted by vanar sena at 1:07 PM on May 31

So two things: 1. Chlorine & associated chemestry and 2. Indoor pools & air quality.

So in reverse order: Indoor pools. People who spend lots of time inside an indoor pool, swimmers and even those not swimming, like lifeguards (who are notrious for their aversion to actually getting any water on them), have higher rates of asthma than the general population. See an article here, or actual research here. Now there is a number of causes for this, including chlorine, but also includes those stupid fountains, bubblers & hottubs, which all aerosolize the fun stuff that then is gets sucked into our lungs.

The water fountains, for example, are pushing water with all sorts of the usual pool water stuff in it - chlorine, skin, sweat, and of course urine. At night, when the fountains and other toys are turned off, their pipes will sit full of uncirulated water over night - and pool chemistry is predicated on being constantly circulated. The chlorine (or whatever chemical proxy is being used) in the standing water will rapidly pass out - leaving just nasty water behind. In the morning the crew comes in, turns on the pump - and pushes all that nasty water into the air - and then you get to breath some of that in. Yum. And the less you know about what is in hottubes the more likely you are to actually use them. It isn't a threat to your health with the hot tubes, they're just a little gross.

The issue with chlorine isn't cancer - in concentrated form it causes massive and terrible chemical burns, and was even used as a weapon along with mustard gas but in a pool it is measured in parts per million, and is not a major health threat at that level.

Aside: the eyes are especially sensitive to the PH of the water - burning or irritation are generally the result of ph being off, not chlorine. Now, high chlorine, which is acidic, is often associated with the ph being way off, so the association of chlorine smell = eye burning water is often correct, but not always. Usually the smell is from the hottube. I have swam in pools with 10 or 20 times the normal amount of chlorine (the test kits aren't great at the high end) but properly buffered with good ph and didn't suffer from burning eyeballs or cancer.
posted by zenon at 3:51 PM on May 31 [3 favorites has favorites]