Are swimming pools a health hazard?
Swimming is an excellent form of exercise. But like many activities, swimming in a pool has its downside.
Despite attempts to disinfect the pool, some pathogens may still lurk in the water. And research suggests that disinfectants may pose their own health hazards.
Swimming in chlorinated pools, particularly indoor pools, might put kids at higher risk for developing respiratory illnesses, including asthma and hay fever.
In addition, there is evidence that disinfectant by-products--formed when chlorinated water is mixed with microorganisms, human body fluids, cosmetics, and sunscreen--can damage your DNA and increase your risk of cancer.
This sounds rather alarming. Does it mean we should keep kids out of the pool?
Not necessarily. It depends on the pool.
And we should keep in mind: Most studies concern kids who swim regularly. A few visits to the wrong swimming pool are unlikely to cause health problems.
So there is reason is reason for concern, not panic, and parents shouldn't feel helpless about the potential risks.
Here is an overview of the latest research on swimming pools, pathogens, and disinfectants. At the end of the article I offer tips on how to minimize risks to your child.
A pool full of humans is liable to contain all sorts of pathogens, and humans are only part of the problem.
Water may be tainted by other sources – organic material derived from decaying leaves, bird droppings, fungi-infested rainwater, or dead organisms.
So disinfecting water is a good idea, and there are several ways to go about it, including ultraviolet radiation and the treatment of water with a copper-silver solution.
But chlorination is the most popular method. It's cheap and relatively effective (Loret et al 2005). When used properly, it protects swimmers from a wide range of dangerous pathogens, including
• E. coli, Rotavirus, Salmonella, and Shigella (each of which may cause gastrointestinal symptoms and, in some individuals, serious illness)
• Adenoviruses (which are linked with gastroenteritis, respiratory infections, eye infections, and other diseases)
• Pseudomonas aeruginosa (which can cause a variety of diseases, including pneumonia and urinary tract infections)
Before the introduction of effective vaccines, chlorination was also one of the only ways to protect swimmers from diseases like polio and hepatitis A.
But no disinfection method is 100% effective. Some pathogens, like the protozoan parasites Giardia and Cryptosporidium, can survive the chlorination process.
Others are destroyed but only after sitting in chlorinated water for 20 minutes or more. If you are unlucky enough to be in the pool immediately after an infected child defecates in the water, your chances of contracting the disease is very high (Kababjian 1995).
And unfortunately, disposable swim diapers offer very little protection. When researchers put them to the test, they found these diapers released most parasite-sized micro-particles within 5 minutes of hitting the water (Amburgey and Anderson 2011).
This might suggest that we’d all be better off swimming in highly-chlorinated pools. But there are health risks associated with chlorination, and these must be balanced against the risks of infection.
Chlorine + humans = harmful disinfectant by-products
Chlorine is itself an irritant, which is why pool managers must limit the amount of chlorine they add to the water. But that’s not the only problem with disinfectants.
Chlorine and chlorine compounds can form harmful by-products when they are mixed with other agents. Unfortunately, these other agents are common in swimming pool water. Perspiration, urine, saliva, hair, skin particles, feces--even cosmetics and sunscreens--all contribute to the formation of disinfectant by-products, or DBPs.
So the typical, chlorinated swimming pool contains DBPs. These can be absorbed through the skin and swallowed. Because the chemicals vaporize into the air, they are also inhaled.
Why is this harmful?
Researchers are still trying to understand how the body reacts to chlorinated water and DBPs.
Like chlorine itself, some DBPs are known respiratory irritants. Maybe long-term exposure to chlorinated water vapor causes inflammation of the air passageways. Maybe it causes oxidative stress, damaging the lungs (Weisel et al 2009).
It also seems that DBPs can damage the DNA.
In a recent study, researchers tested the effects of disinfected swimming pool water on mammalian DNA.
They prepared several solutions—each a different kind of disinfectant mixed with water—and applied them to living mammal cells (Liviac et al 2010).
The results were consistent with other studies (e.g., Woodruff et al 2001). All mixtures induced more DNA damage than plain tap water.
DNA damage is worrying because it increases the risk of cancer. And that’s borne out by research. In laboratory experiments, DBPs have caused cancer in rats (McDonald and Komulainen 2005). And studies have linked exposure to these DPBs with an increased risk of cancer in humans (Richardson et al 2007).
So we have good theoretical reasons to be suspicious about chlorinated pool water.
What about practical observations? Are swimmers becoming ill?
Does swimming in chlorinated water increase your risk of allergies and respiratory disease?
Unfortunately, there isn't any clear answer to this question.
Several studies conducted in Belgium and the Netherlands have reported higher risk of respiratory problems. For example, in one study, kids exposed to chlorinated pools before the age of 2 years were more likely to have developed asthma, respiratory allergies, and bronchiolitis, an inflammation of the bronchioles (2010).
Other research has linked early childhood pool exposure to higher rates of eczema, air passageway inflammation, and sensitization to dust mites (Jacobs et al 2012; Voisin et al 2013).
And a study of more than 800 Belgian teenagers found that kids who spent longer hours in chlorinated pools were more likely to suffer from asthma, hay fever, and other allergies. There was no increased risk of respiratory allergies among teens who swam in pools disinfection with a copper-silver solution (Bernard et al 2009).
Such results sound worrying, but several larger studies--conducted in Germany, Italy, Spain, and Britain--have failed to find any links between swimming pool exposure and respiratory illness.
One of the most compelling is a longitudinal study tracking over 5700 British children from the age of 6 months. Researcher Laia Font-Ribera and colleagues looked for evidence that frequent swimming increased the risk of asthma. They found none. In fact, kids who swam more experienced fewer respiratory symptoms over time (Font-Ribera et al 2011).
Why the conflicting evidence? Maybe the studies reporting problems are in error. But it’s also possible that the risk differs by location.
None of these studies measured the quality of the pool water, and we know that chlorine levels can vary greatly. Different countries set different standards for disinfection. A swimming pool in the United States might have ten times as much chlorine as a pool in Germany (Weisel et al 2009).
Does that mean German pools are safer than American pools? Maybe. But nobody’s attempted to answer that question yet.
Indeed, I haven't seen any epidemiological studies that measured the concentration of disinfectant in the swimming pool water, let alone other factors, like the quality of poolside air.
Perhaps variation among swimming pools can explain why different studies have reported different outcomes. Maybe the studies reporting no effect concerned swimming pools with low levels of disinfectant--or particularly good ventilation.
As I note above, the evidence is inconclusive. The research on DNA and cancer is still in the early stages, and we need more information before we can interpret epidemiological studies.
But meanwhile, concerned parents can follow these guidelines.
• If you can smell the chlorine in the pool environment, there’s too much of it. That’s the rule of thumb offered by researchers Brent S. Rushall and Larry Weisenthal. Tell your local pool manager about your concerns.
• If you frequently swim indoors, find a pool with good ventilation. That means avoiding pools that recirculate air rather than replace it with fresh air. It also means avoiding pools in rooms with low ceilings.
• Avoid swimming pools that don’t insist on cleanliness—including showers before swimming. As noted above, perspiration and other body products mix with chlorine to produce disinfection by-products. When people wash with soap and water before entering the pool, they help minimize the generation of DBPs.
• Tell kids not to pee or spit in the pool. It isn’t just gross—it contributes to the creation of DBPs.
• Encourage your local pool manager to consider research-based alternatives to traditional chlorination. According to the researchers who conducted the DNA study, the safest approach to disinfection may be a combination treatment: UV irradiation with supplemental chlorination (Liviac et al 2010).
• If you are responsible for a pool or hot tub, don’t skip the disinfection process. As noted above, disinfection serves a crucial purpose. The answer isn’t to stop disinfecting pools. The answer is to find ways to disinfect while minimizing other health risks.
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Content last modified 7/13