Health Effects of Chlorine

[chem geek]

I received a PM which I copy below so that this question and my response may be seen by everyone:

Hi I'm from Toronto, Canada and I read your post on pool chlorine levels in swimming pools.

I thought I might ask your views, if you have time, on the effects of chlorine on habitual swimmers like myself.

I've read some material on apparently known effects on competitive swimmers.

For years I've been swimming 7 days a week at an indoor pool for about 40 minutes straight. I shower before and after. I talked to the lifeguard and he said generally the chlorine levels are about 3ppm.

It's never been a concern for me. I've never experienced chlorine as a problem. Do you have any views from a practical standpoint on the long term health risks, e..g, respiratory problems or cancer.

I suspect that being an indoor pool there is no Cyanuric Acid (CYA) in the water. You should ask to verify that, but if that's the case then the active chlorine level is much too strong and will oxidize your swimsuits, skin and hair about 30 times faster than in your own outdoor pool with CYA, assuming you have an FC that is around 10% of the CYA level. My wife experienced this difference every year where her swimsuits would degrade over just one winter season of use in an indoor pool (with 1-2 ppm FC and no CYA) while in our outdoor pool in the summer the swimsuits would last for 6-7 years or more. Also, her skin was flakier and hair frizzier from the indoor pool compared to our outdoor pool.

The rate of disinfection by-products is also dependent on the active chlorine level, especially for the very volatile and irritating nitrogen trichloride most associated with "bad pool smell". Have you noticed a bad smell at the indoor pool or does it just smell like a faint whiff of "clean bleach". If you don't smell nitrogen trichloride, then your respiratory risk may be low and the pool may be properly managed with supplemental oxidation systems, most likely UV. Ask to see what else they are doing -- using UV or ozone and also how much water dilution they do regularly (% of pool volume and how often).

The cancer risk is low, though possibly somewhat higher than it should be unless supplemental oxidation systems are being used or unless the bather load is low. With high bather load and without supplemental oxidation system or coagulation/filtration systems to remove organics from the water, then one can get more chlorinated disinfection by-products. Also, if the fill water has high bromide content, then this is worse with regard to the amount of potential cancer-causing chemicals since the brominated THMs are the ones of concern -- chloroform is not. Even so, the risk is still rather low. See this post for a summary of epidemiological studies on chlorinated water.

 

[bobodaclown]

Great info as always.
Thank you chem geek!

 

[NickAdams]

Thank you, yes that's great information. My swimsuits do disintegrate fast at that pool. The bather load can be high at times, plus the lane swim is often preceded by a public swim with sometimes lots of kids, or by an aquafit class.

I'll follow up some of the technical points you mentioned and if I have any more to add or ask I will post to this thread.

Thank you for posting the thread and for the response, much appreciated.

Nick
Toronto

 

[NickAdams]

Tonight before my swim I asked for some info from the lifeguard and he provided it freely. Apologies in advance if anything I say below makes no sense. I'm a layman.

As you suspected, he said they do not use CYA. He did a chlorine test right then and there and it was 5ppm. He said acceptable levels are considered to be up to 10ppm. He didn't do a free chlorine reading at that moment but he said the FC reading earlier today at 2PM was about 3ppm. The PH was 7.2. He said the PH is more of a culprit in swimsuit disintegration that the chlorine level.

They do not use any supplemental oxidation systems. He quipped that they use 1970s technology. They pay close attention to the bather load and, if I heard him correctly, they add 20 gal. of water for every bather. The bather load was about 100-150 per day. However, when I go for the lane swim, it's often just a few people, like tonight, and other nights between 10-20 maximum. The fill water is just tap water. He didn't know about bromide levels in the water.

Other facts:
- He mentioned that they dump muriatic acid (?) in the pool about once a month, something do to with controlling the calcium hardness of the water.
- The pool has large ceiling windows facing south, so it gets a lot of skylight. Not sure if this is a factor.
- it's 25m rectangular pool, standard size for most public pools.
- I don't believe it gets direct outside airflow; the windows cannot be opened.
- I've been swimming there over 10 years and can say I don't recall smelling any bad pool smells or strong chlorine smells.

If you have any thoughts on the additional information above, I would be interested, if you have time. Otherwise, I already learned quite a bit just from your first reply alone. Thank you again, much obliged!

Nick
Toronto

 

[chem geek]

Thanks for the info. Some of the things he said are wrong and I comment on them below.

As you suspected, he said they do not use CYA. He did a chlorine test right then and there and it was 5ppm. He said acceptable levels are considered to be up to 10ppm. He didn't do a free chlorine reading at that moment but he said the FC reading earlier today at 2PM was about 3ppm. The PH was 7.2. He said the PH is more of a culprit in swimsuit disintegration that the chlorine level.

10 ppm with no CYA? Wow. Just so you know, in Europe the German DIN 19643 standard tries to minimize the chlorine level to avoid the side effects of high active chlorine levels including disinfection by-products. They target 0.3 to 0.6 ppm FC with no CYA if there is no ozonation and with ozonation they use 0.2 to 0.5 ppm. In the U.S. the EPA and most state minimums are 1 ppm FC with a minimum recommendation often being 2 ppm. The EPA maximum is 4 ppm but some states such as Florida go up as high as 10 ppm, but that's in part because CYA is used especially in outdoor pools. CYA significantly lowers the active chlorine level. An FC that is 10% of the CYA level is roughly equivalent to an FC of 0.1 ppm with no CYA.

He is wrong that pH is the culprit in swimsuit degradation. You have to get fairly low in pH before that becomes the main issue. It's the active chlorine level that bleaches out and degrades the fibers in swimsuits and also oxidizes skin and hair.

They do not use any supplemental oxidation systems. He quipped that they use 1970s technology. They pay close attention to the bather load and, if I heard him correctly, they add 20 gal. of water for every bather. The bather load was about 100-150 per day. However, when I go for the lane swim, it's often just a few people, like tonight, and other nights between 10-20 maximum. The fill water is just tap water. He didn't know about bromide levels in the water.

It sounds like they are using the old approach of adding high active chlorine levels to meet chlorine demand and "burn off" bather waste as quickly as possible. This tends to keep the measured Combined Chlorine (CC) level lower, but it also tends to produce more of certain disinfection by-products, especially nitrogen trichloride. However, your not smelling bad pool smell would seem to indicate that they aren't having high nitrogen trichloride levels, perhaps due to excellent air circulation since older facilities weren't so optimized on energy efficiency.

- He mentioned that they dump muriatic acid (?) in the pool about once a month, something do to with controlling the calcium hardness of the water.

The muriatic acid will lower the pH and TA levels. It won't affect calcium hardness, but perhaps he meant they do this to keep the pH and/or TA down to prevent calcium carbonate scaling.

- The pool has large ceiling windows facing south, so it gets a lot of skylight. Not sure if this is a factor.

Glass windows will filter out a lot of UV light, but that which remains will be helpful as UV breaks down chlorine into hydroxyl radicals which are powerful oxidizers and helps get rid of some chloramines as well.

- I don't believe it gets direct outside airflow; the windows cannot be opened.

They must be circulating the air somehow, but perhaps via blower units to vents.

- I've been swimming there over 10 years and can say I don't recall smelling any bad pool smells or strong chlorine smells.

That's strange given the high bather load and high active chlorine dosing level, but as I noted perhaps they have good air circulation even if it's not through windows since they don't open.

 

[NickAdams]

Excellent, thank you very much. I guess we like our pool water stronger up here, like our beer. Thanks for making me aware of international and U.S. guidelines. When I get a chance, I want to find out from city officials what the guidelines are in my city.

You're right, although he used the term calcium hardness, he did mention the muriatic acid was to remove calcium scaling.

I never thought the pool had good ventilation as it's below ground level and adjacent to an underground garage at the far end of the pool. When the storeroom door at the far end is open, I used to get a whiff of the exhaust fumes from the garage, but I believe they've since remedied that. At one point I heard they were going to renovate the windows to allow them to open but it never happened. However, it's quite possible, as you suggest, that overall the ventilation from the rest of the complex is pretty good.

One of the lifeguards says he get a rash which he showed me on his arms which he thought was from the chlorine, though I think he said it was an allergy. I had a couple of cracked molars a few years ago and had to get them capped; it never occurred to me it could be from weakened enamel from chlorine, but that possibility occurs to me now. My teeth are otherwise problem free. It so happens I have a dental appointment next week, and I'll ask my dentist what he thinks.

Thank you again. I will gather some more info about local guidelines and other pools' chlorine levels here. I would like to keep swimming every day at that pool, but if necessary I might consider other pools, or possibly cutting back the number of days per week I swim and doing something else on the other days. However, I read that it only takes one night for the chlorine to get cleared from your body. I'm betting the long term risks are not as high as they would be for competitive swimmers who might swim 2-3 times a day and also that the benefits of swimming itself might offset the other health effects. I'm not going to change my habits just yet, but I'll give it some more thought.

If you have any final thoughts, if you wish you can respond. Otherwise, I've gotten a tremendous amount out of this exchange, very much appreciated.

Nick
Toronto

 

[NickAdams]

Just a footnote: I talked to another lifeguard before my swim today and he said they've been having mechanical problem at the pool (they were shut down recently for 3-4 days) and the cholorine levels have been higher than usual. Normally he said they keep them at about 1.5 or 2.

Thanks again.
Nick

 

[chem geek]

1.5 to 2 ppm FC would be better, though still much higher than needed because there's no CYA in the water. It's closer to what my wife experienced when she swam in our local indoor community center pool, but it was so unpleasant and a pain to go there that for the first time this year we kept our pool heated for most of the winter (except perhaps the one coldest month). We didn't have much rain and had more warmer days so this might be an anomaly for this year, but she liked it a lot better since our pool has a much lower active chlorine level (around 0.1 ppm due to the CYA).

Chlorine itself is unlikely, even at 5 ppm FC with no CYA, to cause rashes, but some disinfection by-products (chloramines) can be irritating so that is more likely to be the cause unless the skin already has some damaged areas where the dead skin layer has already been removed in which case chlorine could be irritating. As for your teeth, it's low pH that is much more harmful to enamel. If a pool is using an acidic source of chlorine such as Trichlor tabs/pucks or chlorine gas (for some older commercial pools), then the pH can get too low and that is what harms teeth. The high chlorine at a normal pH probably doesn't cause any issues. In the U.S., tap water can contain up to 4 ppm FC and has no CYA.

Chlorine doesn't get cleansed from the body because it never gets into the body. Chlorine is fast-reacting with some chemicals (ammonia especially) so it reacts with the outer layers of your skin -- the Stratum corneum (horny layer) that has mostly dead skin cells that are shed. It won't penetrate very far, but high active chlorine levels will make such skin more flaky as a result as a sort of chemical exfoliation. Even if you drink chlorinated water, the chlorine reacts with your saliva before it gets to your stomach.

It is certain chlorinated disinfection by-products that react much more slowly and can penetrate more deeply. Some of these are also volatile so you can breathe them into your lungs. One group of such chemicals that have high dermal absorption and are volatile as well are the trihalomethanes (THMs). There are four of them, three of which contain bromine and are the ones of concern since they can cause cancer. In a chlorine pool where the bromide level of the water is low, these three are generally found in very low concentrations. The fourth one, chloroform, is found in higher concentrations especially in swimming pools since it's a by-product of chlorine reacting with certain organics. However, chloroform does get flushed from the body rather quickly, usually in minutes to hours as it is measured in exhaled air right after swimming and it is not carcinogenic -- it only can cause cancer at cytotoxic levels which are very, very high. See this post for technical details and links to scientific papers.

 

[NickAdams]

I will do so. Thank you very much for all the info and have a good weekend.