Does Chlorine Cause Cancer?

Any thoughts that constant exposure to chlorine might be a contributing environmental factor to cause cancer?
The science says chlorine in of itself isn’t the problem. The problem is disinfection by-products (DBPs) and the worst of the worst are caused by urine and body fluids containing ammonia, forming chloramines. Chlorine consumes bad stuff in the water, and has to be flushed out once it turns to chloramine. If you smell chlorine that is usually chloramine gas trying to release into the air. If it’s allowed to sit unchecked in the water it is really bad. There are solutions: breakpoint chlorination, ORP, and proper ventilation are stressed in pool operations training courses.
Up until recent years swimming pools were basically run by hand. Think about how many times someone asks here on the message board “how many times a day should I check?“.  The pool should be checked as much as possible and continually electronically monitored if possible to prevent chloramine from forming. Every time the bather load increases the risk increases and the chemical strategy has to be changed, but most of the time that’s not happening. Most of the time at the end of the day the swimming pool guy comes and throws some “super shock” in the pool and that’s about it.  The swimming pool industry is huge and has a big lobby believe it or not and nobody wants to talk about the fact that DBPs have been linked to cancer within repeated and long term exposure. Where as: Total Chlorine = Free Chlorine + Combined Chlorine. Combined Chlorine is the bad stuff and there are lots of ways to deal with it, but there’s no easy magical solution. The way a swimming pool works is complex, but must be understood to create a healthy environment for it’s users. Unfortunately most swimming pools are not run properly.
Here are some cited relevant studies taken from an email sent by Dr. Bruce Becker April 18th 2016 via ATRI list.
Hang, C., et al. (2016). “Occurrence and health risk assessment of halogenated disinfection byproducts in indoor swimming pool water.” Sci Total Environ 543(Pt A): 425-431.
Swimming pool disinfection byproducts (DBPs) have become a concern in many countries all over the world. In this study, the concentrations of several categories of DBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HKs) and trichloronitromethane (TCNM), in 13 public indoor swimming pools in Nanjing, China were determined, the correlations between DBPs and water quality parameters as well as between different DBP categories were evaluated, and the health risks of the DBPs to human were examined. The results indicate that the DBP levels in the swimming pools in Nanjing were relatively high, with HAAs as the most dominant category, followed by THMs, HANs, HKs and TCNM sequentially. Bromochloroacetic acid (BCAA), trichloromethane (TCM), dichloroacetonitrile (DCAN), and 1,1,1-trichloropropanone (1,1,1-TCP) were the most dominant species among HAAs, THMs, HANs, and HKs, respectively. For all the different categories of DBPs, the concentrations in the pool disinfected with ozonation/chlorination were lower than those in the pool disinfected with chlorination. The DBP levels were generally not affected by the number of swimmers and the DBP levels on different dates were relatively stable. Besides, the chlorine residual seemed to be a critical concern in most of the swimming pools in this study. Moreover, there were some correlations between DBPs and water quality parameters as well as between different DBP categories. It is to be noted that the predicted cancer and health risks of the DBPs in these swimming pools were generally higher than the regulatory limits by USEPA, and thus DBPs in these swimming pools should be concerned.
Walse, S. S. and W. A. Mitch (2008). “Nitrosamine carcinogens also swim in chlorinated pools.” Environ Sci Technol 42(4): 1032-1037.
Highly carcinogenic N-nitrosodialkylamine (nitrosamine) disinfection byproducts were quantified in chlorinated swimming pools, hot tubs, and aquaria. N-Nitrosodimethylamine, the most abundant nitrosamine detected, was measured in swimming pools and hot tubs at levels up to 500-fold greater than the drinking water concentration of 0.7 ng/L associated with a one in one million lifetime cancer risk. Temperature, enclosure, amine and nitrite precursor loading, and the use of disinfection schemes with reduced chlorine doses contributed to statistically significant variability in its occurrence. N-Nitrosodibutylamine and N-nitrosopiperidine were also detected but together represented <5% of the total analyte distribution. The presence of N-nitrodimethylamine at levels comparable to N-nitrosodimethylamine points to a competition between the nitration and nitrosation of amines in chlorinated recreational waters. Since nitrosamines can cause bladder cancer, the significance of our measurements needs clarification with respect to recent epidemiological results that are suggestive of a link between swimming in chlorinated pools and bladder cancer.
Zwiener, C., et al. (2007). “Drowning in disinfection byproducts? Assessing swimming pool water.” Environ Sci Technol 41(2): 363-372.
Disinfection is mandatory for swimming pools: public pools are usually disinfected by gaseous chlorine or sodium hypochlorite and cartridge filters; home pools typically use stabilized chlorine. These methods produce a variety of disinfection byproducts (DBPs), such as trihalomethanes (THMs), which are regulated carcinogenic DBPs in drinking water that have been detected in the blood and breath of swimmers and of nonswimmers at indoor pools. Also produced are halogenated acetic acids (HAAs) and haloketones, which irritate the eyes, skin, and mucous membranes; trichloramine, which is linked with swimming-pool-associated asthma; and halogenated derivatives of UV sun screens, some of which show endocrine effects. Precursors of DBPs include human body substances, chemicals used in cosmetics and sun screens, and natural organic matter. Analytical research has focused also on the identification of an additional portion of unknown DBPs using gas chromatography (GC)/mass spectrometry (MS) and liquid chromatography (LC)/MS/MS with derivatization. Children swimmers have an increased risk of developing asthma and infections of the respiratory tract and ear. A 1.6-2.0-fold increased risk for bladder cancer has been associated with swimming or showering/bathing with chlorinated water. Bladder cancer risk from THM exposure (all routes combined) was greatest among those with the GSTT1-1 gene. This suggests a mechanism involving distribution of THMs to the bladder by dermal/inhalation exposure and activation there by GSTT1-1 to mutagens. DBPs may be reduced by engineering and behavioral means, such as applying new oxidation and filtration methods, reducing bromide and iodide in the source water, increasing air circulation in indoor pools, and assuring the cleanliness of swimmers. The positive health effects gained by swimming can be increased by reducing the potential adverse health risks.
Villanueva, C. M. and L. Font-Ribera (2012). “Health impact of disinfection by-products in swimming pools.” Ann Ist Super Sanita 48(4): 387-396.
This article is focused on the epidemiological evidence on the health impacts related to disinfection by-products (DBPs) in swimming pools, which is a chemical hazard generated as an undesired consequence to reduce the microbial pathogens. Specific DBPs are carcinogenic, fetotoxic and/or irritant to the airways according to experimental studies. Epidemiological evidence shows that swimming in pools during pregnancy is not associated with an increased risk of reproductive outcomes. An epidemiological study suggested an increased risk of bladder cancer with swimming pool attendance, although evidence is inconclusive. A higher prevalence of respiratory symptoms including asthma is found among swimming pool workers and elite swimmers, although the causality of this association is unclear. The body of evidence in children indicates that asthma is not increased by swimming pool attendance. Overall, the available knowledge suggests that the health benefits of swimming outweigh the potential health risks of chemical contamination. However, the positive effects of swimming should be enhanced by minimising potential risks.
Villanueva, C. M., et al. (2007). “Bladder cancer and exposure to water disinfection by-products through ingestion, bathing, showering, and swimming in pools.” Am J Epidemiol 165(2): 148-156.
Bladder cancer has been associated with exposure to chlorination by-products in drinking water, and experimental evidence suggests that exposure also occurs through inhalation and dermal absorption. The authors examined whether bladder cancer risk was associated with exposure to trihalomethanes (THMs) through ingestion of water and through inhalation and dermal absorption during showering, bathing, and swimming in pools. Lifetime personal information on water consumption and water-related habits was collected for 1,219 cases and 1,271 controls in a 1998-2001 case-control study in Spain and was linked with THM levels in geographic study areas. Long-term THM exposure was associated with a twofold bladder cancer risk, with an odds ratio of 2.10 (95% confidence interval: 1.09, 4.02) for average household THM levels of >49 versus < or =8 micro g/liter. Compared with subjects not drinking chlorinated water, subjects with THM exposure of >35 micro g/day through ingestion had an odds ratio of 1.35 (95% confidence interval: 0.92, 1.99). The odds ratio for duration of shower or bath weighted by residential THM level was 1.83 (95% confidence interval: 1.17, 2.87) for the highest compared with the lowest quartile. Swimming in pools was associated with an odds ratio of 1.57 (95% confidence interval: 1.18, 2.09). Bladder cancer risk was associated with long-term exposure to THMs in chlorinated water at levels regularly occurring in industrialized countries.

Sick Patient in the Pool

Q:   Two connected and similar questions that have been taken from the ATRI list serve. 

#1 Emergency respond please!!

Just had a patient call to tell me she has an outbreak of shingles. She was in the pool Wednesday!
My question is:
DOES CHLORINE KILL THIS TYPE OF VIRUS?? Should I increase chlorine levels?


#2  We have a new patient sent to us by an orthopedic physician asking for pool therapy.  The patient is very obese and shared that she has ongoing yeast infections in the skin folds of her body.  She is also a diabetic.  Is there some kind of a barrier cream that can be applied to the affected areas or is it not advisable for her to enter our pool.

Our population is primarily seniors and we are concerned for their well being.

Has anyone had experience with this type of yeast infections? And what have you done for them?



#1   As long as you kept residual free chlorine in your pool during and after the use of the pool you are ok and don’t need to do anything. You do want to check you maintenance log and see if the PH and CL were/are up to par. If there was not a free CL residual of one, and a correct PH level you will want to contact the health department. In that case, they will tell you what to do next. It really doesn’t matter what the bug is that your trying to kill: yeast, fungus, virus, bacteria they are no match for the oxidative / disinfection properties of free chlorine in conjunction with proper PH levels. That’s why people keep halides in their pools, to keep it safe for everyone who uses it. Of course there is always the exception such as in the case of diarrheal discharge. This is all covered in my upcoming AFO course.


#2   With regard to this person with fungal issues: If they have open sores they should not enter the pool. Otherwise, chlorine will protect pool users from transmittable illness because it kills microbes instantly, BUT you have to make sure this person baths properly with soap thoroughly before they get in. If someone gets into the pool dirty it can bring down the free residual CL quickly and that’s a big problem, one that could manifest all of your deepest fears. Does the pool have an automatic feeder monitoring ORP to keep up with the demand for chlorine to disinfect the pool? If it does and if your aquatic facility operator is keeping up with the water it’s really no different than any other day at the pool.

I have an upcoming Aquatic Facility Operator course coming up in Phoenix, Arizona November 12th and 13th geared towards to aquatic fitness community. Please consider coming if you work in the water and would like to learn about swimming pools in plain easy to understand language. This course will be eligible for continuing education credit.

My Pool is Humid – Do I need a fan?

Q: Anybody have recommendations about what fans to use in pool areas to circulate the air?


A: It is not so much a question of what fan you need but rather how you manage your indoor air. The following is an excerpt from the Aquatic Facility Operator Manual:

Air Temperature Control – Proper air temperature control must be maintained in the natatorium, through air heating and cooling, to ensure year-round comfort while minimizing pool-water evaporation. Improper temperature management can result in excessive humidity levels and unnecessary pool-water heating . Temperatures and relative humidities are sometimes maintained by simply bringing in, and heating large amounts of outdoor air and exhausting equal amounts of warm, humid air- an expensive process. (an illustration is given page 20-4) Recommended air temperatures are often just 2 F degrees above the water temperature. With low humidity and little air movement, this might feel cold.”  (Williams, 20-4)
This section is preceded by an explanation of the result of excess humidity which is distilled water. Distilled water accumulating throughout the aquatic facility is a very caustic agent and eats away at all fixtures.
So basically if you are looking for a new fan, it sounds like you are caught in a situation where you are trying to keep your air too hot for your water to make people comfortable and are constantly having to push hot air out in order to control the humidity. You will want to speak with an HVAC expert who specializes in aquatic facilities to re-engineer your facility with proper heat and humidity exchange. Otherwise you can look forward to high electricity bills and a constant tug of war using any fan you like.
Williams, K. G., & Young, R. A. (2011). The Aquatic Facility Operator Manual.

Salt Water Swimming Pools Vs. Chlorine Swimming Pools

Q: My facility has used chlorine in our pools with patients. (we have had very little complaints since our facility checks the water 3xdaily and makes adjustments)  The facility is now looking at the new trend of rehab facilities changing to salt water pools for their patients.  Does anyone have experience of using salt water?  I am interested in pros, cons, and any input!  Any resources would be of great help.

A: The salt used in pools is a NACL molecule.  What a salt water system does is apply electricity to split those molecules to divide the NA(sodium) from the CL. CL is of course Chlorine. Instead of adding another chemical like bleach or a calcium compound, salt is inserted into the water and the Chlorine is generated using the electrical process. It is still a chlorine pool. It is more expensive to maintain if it is not maintained at the manufacturer recommended PH levels extremely consistently because of equipment failure and salt scaling in the pipes. Usually there is a better option than a salt generation system unless you just want it to capitalize on the misconception that a salt water pool is not a Chlorine pool, which is definitely financially advantageous in some cases but maybe not very honest.

The same parameters apply in all Chlorine pools and most pool chlorine issues are caused by a failure to maintain breakpoint chlorination not the type of chlorination system.