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Thread: Asthma and Chlorinated Pools

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    Asthma and Chlorinated Pools

    WARNING: This topic may be controversial.

    2003 Study of Indoor Chlorinated Pools

    In 2003, Dr. Alfred Bernard (and others) published this article associating indoor chlorinated pool use with a greater incidence of asthma and seeing that nitrogen trichloride may be one of the causes.

    This study made some sense in that nitrogen trichloride was shown in other studies to be a strong irritant and since Cyanuric Acid (CYA) was not used in most indoor pools and that many such pools may have had a somewhat higher (1 ppm FC or more with no CYA) chlorine level such that the nitrogen trichloride levels could be unacceptably high. This could be especially true with the lower amount of fresh-air exchange associated with modern energy-efficient indoor pool buildings. There were other studies by others later, but I'll talk about that after discussing a more recent study by Dr. Bernard.

    2008 Study of Outdoor Chlorinated Pools

    In 2008, Dr. Bernard published this article associating outdoor chlorinated pool use with a greater incidence of asthma. This study showed a large correlative increase between asthma and the number of cumulative lifetime (childhood) hours in chlorinated outdoor pools. The study used questionnaires given to parents of 14-16 year-old students in three French cities. This was a "snapshot-in-time questionnaire" study, not a longitudinal study that tracks what goes on over time to a random sample of subjects.

    There were a few strange things reported in the full study (which I paid for and downloaded) which seemed at odds with the study conclusions. First is that "when considering the whole population, no significant association emerged between asthma and the attendance at indoor chlorinated pools, whether cumulative over lifetime or during early childhood." This seems at odds with Dr. Bernard's earlier study. At the town with the indoor copper-silver sanitized pool at school, the ever asthma was 10.6% and current asthma was 5.9% (out of 357 students) while at the other towns with indoor chlorinated pools, the ever asthma was 10.3% and 9.9% and the current asthma was 6.0% and 7.1% (out of 349 and 141 students), respectively. 95+% of the students spent time in indoor chlorinated pools. In addition, roughly half spent time in residential and nonresidential outdoor chlorinated pools and these outdoor pools were the focus of the study in terms of correlations. Also, students in the two towns without copper-silver pools spent (for the median) about 80% more time in their chlorinated indoor pools than those students did in the copper-silver pool (and total time in all pools as well), yet the overall population numbers don't show an increase in asthma. So whatever conclusions this study makes with regard to outdoor chlorinated pools needs to explain 1) why this study seems to contradict the earlier indoor chlorinated pool study and 2) what uniquely makes outdoor pools (both residential and nonresidential) different.

    A second strange item was the statement in the study that "the cumulative attendance at either type [residential and nonresidential] of outdoor pools was indeed not significantly different between adolescents diagnosed with asthma and their peers without asthma." This makes absolutely no sense given the study's demonstrated correlation between the number of hours (cumulative attendance) in outdoor pools and the increased percentage of those with ever asthma or current asthma. Correlations are a two-way street: if X is correlated with Y, then Y is correlated with X. Correlations don't determine cause and effect, but if there was a correlation between cumulative time in outdoor pools and odds of asthma, then the converse HAS to be true as well -- that is, adolescents diagnosed with asthma have to have had higher cumulative attendance in outdoor pools. The only thing I can figure here is that the correlation claim between outdoor chlorinated pool time and asthma is done on a much smaller sample using students who had asthma while the converse statement I quoted above is looking at the much larger overall population.

    The study talks about why it must be the chlorinated pools causing the asthma and not that children with asthma spent more time in pools by making the quote I gave above and by noting that doctors typically recommend using indoor pools where there is warm moist air and not swimming in general. I found it interesting that apparently the questionnaire didn't ask the parents if they changed their children's time in pools or the type of pools after the diagnosis. Also, there was no attempt at analyzing the pools themselves in terms of their water chemistry. It's true that this is impossible since a historical analysis would be needed, but it would be interesting to at least get an idea of what FC, CYA, etc. levels are at the various pools that were used. Dr. Bernard does note that residential pools tend to use stabilized chlorine products, but that's about all that is said on this subject.

    2008 Meta-Analysis of Chlorinated Swimming Pool Studies

    In 2008, this meta-analysis (i.e. a study of numerous studies) showed no significant correlation between swimming during childhood and asthma. So the Dr. Bernard studies should be taken in that context. [EDIT] A recent conference described here concluded a suggestive link that was not conclusive, pointed out certain problems with existing studies, and recommended specific protocols to determine clear associations. [END-EDIT]

    Analysis

    The Dr. Bernard study published in 2008 speculates that it is the higher Free Chlorine (FC) levels typically found in outdoor pools that is the source of the problem and he speculates that it is hypochlorous acid outgassing from the pools. I had sent Dr. Bernard E-mails describing the chlorine/CYA relationship starting in August, 2007 and most recently in May, 2008 with info regarding the implications to nitrogen trichloride production. He never responded so probably didn't read it and in any event may have been too late for modifying his paper. Though it is not certain that the nonresidential pools used stabilized chlorine since sometimes they do not due to high bather loads that overwhelm the chlorine demand (so CYA isn't as helpful), the residential pools more likely than not used stabilized chlorine since it is not very economical to use chlorine otherwise in low-bather load pools exposed to sunlight. In such pools, the outgassing of hypochlorous acid is reduced by orders of magnitude due to CYA and the disinfection by-products are also reduced significantly due to the low bather load.

    So if we take Dr. Bernard's 2008 study at face value (being extra conservative), what could cause asthma in children swimming in these pools? If it's not volatile disinfection by-products (due to low bather load) and it's not outgassing of chlorine itself (due to CYA) and it's not skin absorption (CYA skin absorption is negligible so chlorinated cyanurates are probably similar) and it's not drinking the water (since chlorinated drinking water has not seen these associations), then that pretty much leaves getting chlorinated water directly into the lungs or into breathing passageways. If pool water gets into the body, then the CYA level isn't very relevant and it is the Free Chlorine (FC) level that matters in terms of total exposure. The CYA will slow down reaction rates, but it is the FC level that is the total capacity and therefore total exposure. Though hardly scientific, I have noticed when swimming in public pools that it seems far more likely for young children to 1) get water up their noses or 2) swallow pool water into their lungs leading to coughing. Whether this is due to less coordination of breathing when young or the increased head dunking, splashing, and related activity, I don't know. To be clear, the distinction is between gaseous products that are unlikely to be at issue here vs. aerosols and larger quantities of chlorinated water.

    If one wants to minimize exposure (and I'm not recommending this; just laying it out for those that want to know), then one simple thing would be to use nose plugs which would at least reduce the amount of chlorinated water going through that route. I'm not sure what one would do to reduce swallowing/gulping accidentally into the lungs. As for having a lower Free Chlorine (FC) level, that can be done at extra expense by using algicide products and possibly enzyme or non-chlorine shock products if the bather load is higher such that more oxidation is needed. Of course, one never knows what getting those products into the lungs might do so it's probably better to focus on reducing exposure to the lung of any pool water regardless of what is in it.

    Richard
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    Re: Asthma and Chlorinated Pools

    So Richard, put it in simple terms for this simpleton! Are you saying that chlorinated pools can be bad for asthmatics...as in the bleach of our BBB... or that pretty much any pool, unless it is treated with chlorine-free chemicals, is not good for asthmatics? Our nine-yr old son, who spent years 2-6 in the ER appx once per month, has had no problems with our pool since we went BBB last summer. I have asthma and have had no problem at all. In fact, neither of us has had any asthma for nearly two years now!

    So I'm a little confused, which is no big surprise!
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    Re: Asthma and Chlorinated Pools

    If one believes the study conclusions, then it's that swimming in outdoor chlorinated pools increases the risk of developing asthma. And since the same conclusions were made for "ever asthma" (i.e. ever having asthma) and "current asthma" (i.e. currently diagnosed with asthma) the implication is that the swimming doesn't help, at least for children. Your experience demonstrates otherwise at least for current asthma.

    Since the meta-analysis of many studies didn't show a correlation (i.e. did not support the Bernard study) and there were questions/issues such as those I raised, I wouldn't read too much into Dr. Bernard's study. Whether you are using bleach or another source of chlorine shouldn't make any difference; as you point out, one would have to be chlorine-free based on Dr. Bernard's conclusions (assuming the copper-silver pools was chlorine-free; he didn't say but I presume it's either chlorine-free or very low in chlorine). Since there were no measurements of pool water chemistry levels, one can't know what, if anything, is the cause.

    If your own experience is that of fewer problems with your BBB pool, that's what is most important. With the study that was done, we have no idea how those pools were managed and again, this was just one study that had some inconsistencies and is not supported by other studies overall.

    Richard
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    Re: Asthma and Chlorinated Pools

    Then I would almost have to suspect some ulterior motive in such a study, i.e., making chlorine a no-no for pools. Seems I read a report last year about some government study that was trying to do away with chlorine altogether, saying it was "dangerous" to our health. It didn't have to do with pool maintenance. I was researching TFP's claims on BBB (doing my homework, ya know) before I decided to take the BBB plunge and prove to DH that it would be ok. But I remember thinking "WOW! That would be disastrous for all the BBB'ers if they outlawed bleach!"

    Thanks for your post, Richard.
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    Re: Asthma and Chlorinated Pools

    Quote Originally Posted by chem geek
    At the town with the indoor copper-silver sanitized pool at school, the ever asthma was 10.6% and current asthma was 5.9% (out of 357 students) while at the other towns with indoor chlorinated pools, the ever asthma was 10.3% and 9.9% and the current asthma was 6.0% and 7.1% (out of 349 and 141 students), respectively.
    This says that asthma incidence among indoor pool users is not correlated with sanitizer type (chlorine v. non-chlorine) and so nitrogen trichloride would be absolved (or at least not be a significant contributor). Granted the populations are pretty small. I am a little confused because this data seems to be from the 2008 study which you said was outdoor pools? Did they look at both, in 2008?

    Quote Originally Posted by chem geek
    I found it interesting that apparently the questionnaire didn't ask the parents if they changed their children's time in pools or the type of pools after the diagnosis.
    A key piece of information. If heavy pool users have a higher incidence of asthma, "the correlation goes both ways" means that asthmatics overall are heavier pool users than the general population. But if they are drawn to pool use because of the diagnosis, then any speculation regarding the mechanism whereby pool use "causes" asthma is just totally pointless; the initial incidence of asthma would not be correlated with pool use.

    Thanks,
    --paulr
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    Re: Asthma and Chlorinated Pools

    Great research Richard,

    Fatally flawed is the term that comes to mind regarding Dr Bernard's report. Of all the report's I have read Dr Bernard is linked or mentioned so it is brilliant to have you follow this up.

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    Re: Asthma and Chlorinated Pools

    The 2008 study looked at three towns where the students had access to BOTH indoor and outdoor pools. It sounded like the schools themselves had indoor pools; one was copper/silver while the other two were chlorinated. The survey then asked about additional use of outdoor pools in two categories: public nonresidential and residential. The public nonresidential pools included those visited on holidays. Basically, virtually all of the students swam in the indoor pools (825 students out of 847) and more than half also swam in outdoor pools (514 out of 847). 339 students swam in the indoor copper-silver sanitized pool while 486 swam in indoor chlorinated pools. Dr. Bernard used multi-variate analysis to find correlations between the different pool types.

    Yes I found it very surprising that this report said there wasn't a correlation between asthma and indoor pools since that was one of the implied conclusions of the earlier 2003 study. Dr. Bernard did find such a correlation when looking at a smaller subset of those with a low exposure to outdoor pools (< 100 h) and highest indoor pool attendance (> 500 h) which had a significant increase in the risk of ever asthma and a nonsignificant increase in the risk of current asthma. He goes on to state that they "found no significant associations between any of the studies outcomes and the attendance of the copper-silver sanitised pool." However, he did not publish any specific data associated with that pool, unlike the statistical data and charts shown for the outdoor chlorinated pools.

    I think part of what is going on here is that the sample size is not that large to begin with (847 total students) so when taking smaller samples of those with ever asthma (88 students) one gets into more statistical noise and when looking at the even smaller samples of those with higher cumulative swimming hours the data can get pretty dicey.

    Dr. Bernard tries to address the issue of causation by addressing the issue of potential bias in the questionnaire and by stating that the cumulative attendance at outdoor pools wasn't significantly different between adolescents diagnosed with asthma and their peers without asthma (a statement that makes absolutely no sense given the correlations found). There were also no public outdoor pools in the studied centres so the outdoor pool use was only residential or on holidays (and given the median lifetime swimming in such holiday pools of 126 to 306 hours, that's a lot of time on holiday). Dr. Bernard found the same outdoor pool associations with asthma with nonresidential and residential pools. Dr. Bernard notes that a reverse causation would imply that parents installed pools in their backyards after an asthma diagnosis or increased their use of pools on holidays. He didn't consider that maybe those with existing pools would have their children swim more frequently after a diagnosis and that using one's own residential pool would be more convenient. He notes that "asthmatics are advised to swim not in outdoor pools but in indoor pools, in which the warm and humid atmosphere is less likely to trigger asthma symptoms".
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    Re: Asthma and Chlorinated Pools

    Well, if asthmatics are encouraged to swim in indoor pools, then of course you'd expect to find a correlation between ever asthma and indoor pool use. Maybe Dr. Bernard meant he didn't find enough correlation to suggest anything more than that? But to support that conclusion he'd need to show what sort of correlation to expect based on that encouragement, and then show that the actual correlation differed significantly from the expectation. It doesn't sound like he did that.
    --paulr
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    Re: Asthma and Chlorinated Pools

    aside from the fact that there are some fundamental flaws in the whole thing

    i would also have been interested to see what kind of result they got to base level asthma they got in a town with no access to a swiming pool, either indoor or outdoor

    guess this will be another paper to be apearing on the snakeoil websites

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    Re: Asthma and Chlorinated Pools

    It must be true. It just come over on Yahoo News...

    I love the following quote: "Bernard said that if you have a backyard pool, you should use as little chlorine as you can to safely disinfect the pool. He said that many people over chlorinate their pools to get clear blue water. "



    Sounds like someone works for Nature2.
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    Re: Asthma and Chlorinated Pools

    LOL, my husband came home tonight asking if I'd read the article. I told him that the folks on TFP have already covered it. Way to be on top of the propaganda job guys!
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    Re: Asthma and Chlorinated Pools

    I just wanted to update this thread with the latest info. The Committee on the Medical Effects of Air Pollutants (COMEAP) has put out this statement on "Asthma and exposure to chlorine and associated reaction products at swimming pools". In short, it shows that there is less of a casual link of swimming in chlorinated pools to asthma based on the more recent studies than was concluded in their earlier review in 2007 and that review showed a rather weak link.

    As they recommend, disinfection by-products should be minimized consistent with appropriate sanitation. That should always be the goal. I believe that residential outdoor pools are of the least concern due to the low bather loads, exposure to UV from sunlight, and better air circulation compared to indoor commercial/public pools which are the most problematic.
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    Re: Asthma and Chlorinated Pools

    I'd be curious to know if it mattered that it was FC or CC.....
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    Re: Asthma and Chlorinated Pools

    The issue is mostly with nitrogen trichloride, but having a higher CC doesn't necessarily mean that one will have more of this irritating chloramine. With CYA in the water, the monochloramine and dichloramine and chlorourea levels can all be higher (and all measure as CC), but the nitrogen trichloride will be lower because the active chlorine level is lower. The reports of the most problems are with high bather-load indoor pools and they aren't using any CYA in the water. The resulting higher active chlorine level produces more nitrogen trichloride. In an outdoor residential pool, the CC is usually very low (usually <= 0.2 ppm; often <= 0.4 ppm) and the nitrogen trichloride is negligible.
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    Re: Asthma and Chlorinated Pools

    Updating this thread with a 2009 study from Bernard entitled Impact of Chlorinated Swimming Pool Attendance on the Respiratory Health of Adolescents. This study was similar to his 2003 study in that it was primarily for indoor pools only where FC levels were regulated to be 0.5 to 1.5 ppm and CC levels were regulated to be < 2 ppm until 2003 and < 0.8 ppm after 2003. Since this was an epidemiological study, actual water chemistry parameters are not known and were only estimated based on regulations. This paper looked at correlations with asthma, hay fever, and allergic rhinitis. The study questionnaire was based on total lifetime cumulative swimming hours for both indoor and outdoor pools, but the primary pools accessed were indoor and unfortunately the study did not break out any differences.

    Note that the active chlorine level in pools we use with CYA is generally equivalent to < 0.1 ppm FC with no CYA and there should be far fewer volatile disinfection by-products as well.
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