PS. Great site, after we bought this house I was reading about all the ill affects chlorine has on health and how you should put a whole house carbon water filter in your main water line so you would not absorb chlorine through your skin. If I read Chem Geek correctly chlorine is not absorbed through the skin. He is very knowledgeable and documents his references frequently to support his position. I was thinking about filling the pool in until I read a lot of his posts. If Richard has any time to comment on chlorine being absorbed through skin and ingestion of chlorinated (non filtered) water as a health hazard I would be very interested. He is this sites greatest asset, not that everyone else isn't, but very impressed with his knowledge and stick to the facts approach. I just do not know where he finds all the time to type this, let alone research it. Thank you everyone for your time and willingness help.
Chlorine and Skin
Chlorine
does react with skin and does so fast enough that very little gets through more deeply to be absorbed. So I wouldn't say that chlorine is not absorbed through the skin so much as chlorine reacts with ammonia and other organics in sweat and skin such that chlorine itself does not penetrate deeply. The issue is never about chlorine itself anyway, but rather the disinfection by-products from chlorine, so some of those chlorinated organics. The same is true for drinking water with chlorine. The issue is not the chlorine itself, but rather the chlorinated organics and by the time the drinking water reaches your stomach, it is no longer chlorine but instead chlorine reacting with your saliva and organics.
Chlorine Disinfection By-Products
So for the downsides of chlorine the best threads to read would be
Asthma and Chlorinated Pools which basically concludes that there isn't a linkage except possibly in the most heavily used pools with professional swimmers and
New Chlorine Scare that I start with my post in that thread where here the correlations are more legitimate but again show that the problems are primarily related to high bather load and higher chlorine levels (no CYA used) and higher bromide levels (brominated organics worse than chlorinated ones) and even then they aren't that strong. This latter point regarding bromine is also discussed at length in the thread
The forgotten alternative sanitizer for pools and spas... where someone was promoting iodine instead of chlorine or bromine yet that is the worst halogen by far if one is to choose among the three. I will say that there have been poorly run commercial/public high bather-load pools including many used for swim meets and other competition that have been a problem for swimmers, but it doesn't have to be that way and not all such pools operate poorly (in general, Europe does a far better job in this area than the U.S.). A fairly detailed summary of chlorine health risks mostly from a drinking water perspective is in the document
Environmental Health Criteria 216 "Disinfectants and Disinfectant By-Products" and the conclusions are the following:
Epidemiological studies have not identified an increased risk of cardiovascular disease associated with chlorinated or chloraminated drinking-water. Studies of other disinfectants have not been conducted.
The epidemiological evidence is insufficient to support a causal relationship between bladder cancer and long-term exposure to chlorinated drinking-water,THMs, chloroform or other THM species. The epidemiological evidence is inconclusive and equivocal for an association between colon cancer and long-term exposure to chlorinated drinking-water, THMs, chloroform or other THM species. The information is insufficient to allow an evaluation of the observed risks for rectal cancer and risks for other cancers observed in single analytical studies.
Studies have considered exposures to chlorinated drinking-water, THMs or THM species and various adverse outcomes of pregnancy. A scientific panel recently convened by the US Environmental Protection Agency reviewed the epidemiological studies and concluded that the results of currently published studies do not provide convincing evidence that chlorinated water or THMs cause adverse pregnancy outcomes.
Chlorine in the Home
The risk of chlorine exposure in terms of health problems is very low, but there may be some individuals who are more sensitive to certain chemicals so if one wants to minimize exposure then one certainly has a rational reason to do that. For drinking water, it is trivial by using a carbon block filter such as from
Multi-Pure though in practice most people aren't drinking most of their water from the tap. As for showers, that is more of a challenge due to the hotter water since a carbon filter won't work in that situation so what is done there is to use a reducing agent in a shower filter. The reason a shower might be more of an issue is that if it's hot and steamy than you are breathing in more chlorine or chloramine (depending on what your water district is using) so you can create chlorinated organics in lung tissue so closer to getting them into the bloodstream compared to their creation in skin or in the stomach where acidic conditions may destroy some of them. Again, overall risk is very low, but if you wanted to focus on something then that would be the most relevant with regard to tap water. You could use a whole house filter if you wanted to, but that's obviously a lot more expensive.
Chlorine in Pools -- CYA makes all the difference
The main difference with the chlorine in pools managed in the way this forum describes is that there is Cyanuric Acid (CYA) in the water that significantly cuts down the active chlorine (hypochlorous acid) level by literally more than an order of magnitude -- about a factor of 10 or more compared to pools with no CYA. The active chlorine level in pools at the levels recommended on this forum are equivalent to less than 0.1 ppm FC with no CYA. The chlorine bound to CYA does not absorb through the skin (see
this paper) nor does it react with it as quickly as chlorine -- it reacts no faster than 1/150th the rate (see
this paper). So skin reaction or absorption in pools with CYA is almost a non-issue, but it's not zero as is obvious by the fact that one can smell chloramines on the skin if one is sweaty, but the reaction with organics in the skin is indeed very slow compared to pools with no CYA. The CYA doesn't help with regard to ingestion of pool water since the chlorine is released from CYA as it gets used up, but one does not ingest very much pool water -- certainly no where near the quarts of water one consumes each day (including that in food). As for volatile organics, the bather load in most residential pools is so low that these are negligible and in outdoor pools the UV in sunlight keeps some of these very low due to direct destruction (such as with dichloramine) or preventing their formation in the first place (such as destruction by hydroxyl radicals formed when chlorine breaks down from the UV in sunlight). There is also usually wind to carry away volatiles near the surface, especially as compared to indoor pools.
Chlorine in Spas
Probably the larger risk is with residential spas since the bather load is far higher there. Most people start their soak with a lower level of chlorine so that it isn't as noticeable and in practice that results mostly soaking with monochloramine that doesn't react to produce nearly as many disinfection by-products. Also, CYA is used so again the direct action of chlorine during soaking is minimized. So the issue is more what happens after one doses with chlorine after a soak where the disinfection by-products are then formed. The volatile ones can be outgassed if one opens up the spa and runs jets to air it out before getting in, but there will still be remnants of these chemicals plus the non-volatile ones left in the water. These will build up until the next water change. This is still low risk, but on the spectrum of risk it's higher than in residential pools because of the higher bather-load and the hotter water that volatizes more and the skin is more porous at hotter temperatures as well. Some alternatives to reduce this low risk are to use an ozonator that will oxidize more of the bather waste or to use some (not only, since it's not a disinfectant) non-chlorine shock (MPS) though it isn't a great oxidizer for some things (like ammonia or monochloramine) or use some enzymes. If one wants a non-halogen system, then Nature
2 with its silver ions and used with MPS is an EPA-approved disinfectant combination for spas, but usually requires some chlorine usage once a week or so to keep the water clear.
Relative Risk
One should have some perspective on the kind of risks we are talking about in terms of disinfection by-product exposure. Roughly speaking even in the high bather-load pools of the Barcelona studies we are talking about lifetime cancer risk increases in the 1 in 50,000 or lower range if one were to swim every day. The EPA targets roughly 1 in 1,000,000 for their drinking water contaminant goals. The lifetime risk in outdoor residential pools will be lower than the Barcelona pools so probably somewhere in between the 1 in 50,000 to 1 in 1 million range. The risk in spas might be closer to the Barcelona numbers or possibly higher than that worst case, but still probably not any higher than 1 in 10,000 and that would be a stretch since no studies show anything approaching that level. To put all of this in perspective, the overall cancer incidence (not death) rate is roughly 1 in 220 each year with a lifetime risk of roughly 40% (i.e. 1 in 2.5). If one really wants to try and avoid cancer, there are a lot of areas in one's life one can look at long before worrying about drinking water, showering/bathing, or swimming especially since the latter with exercise helps improve health and reduce disease risk substantially more than any increase from use of chlorine, most especially in outdoor residential pools.
To give you an idea of what we do at home, we have a Multi-Pure filter on a separate tap water line in the kitchen and use Britta portable water containers elsewhere such as in the bathroom. I say "we", but it's really for my wife and not so much for any health reason as for the fact that she doesn't like the taste of the water unless it is filtered. We don't have anything on the shower heads nor any whole house filter and I use chlorine in our pool with CYA where my wife swims nearly every single day for swim therapy.
