Is Chlorine Safe For My Pool?

Updated June 28, 2006 by Emily Main

Piers Keegan asks:

What harm results from using chlorine in swimming pools?

Piers Keegan
Las Vegas, NV

The Green Guide responds

While swimming in a bacteria and pathogen-filled pool poses clear threats to health, chlorine pool sanitizing products are not without risks. Some very harmful substances—dioxins and furans, for example, and also trihalomethanes—can arise when chlorine products come in contact with organic matter, such as leaves and dirt. Dioxins and furans, both reasonably anticipated to be human carcinogens by the International Agency for Research on Cancer (IARC), are organochlorine compounds similar in structure to PCBs. They biodegrade very slowly and therefore build up in the bodies of animals and humans; dioxin and furan have even been detected in breast milk samples. Trihalomethanes—including the carcinogen chloroform—are formed when chlorine reacts with carbon-containing organic matter. They can increase the risk of cancer and may damage the liver, kidneys, and nervous system, and increase rates of miscarriage and birth defects.

Both chlorine and trihalomethanes (predominantly, the carcinogen chloroform) may be found in chlorinated pools, and can be inhaled or absorbed through the skin. Too much chlorine in a pool also can cause skin irritation, eye irritation, and both short and longer-term respiratory problems: coughing, difficulty breathing, and "swimmer's asthma." A study published this June in the American Journal of Respiratory and Critical Care Medicine found that children exposed to chlorine in swimming pools had decreased lung function. An older study, published in the June 2003 Occupational and Environmental Medicine, found that young swimmers had high levels of proteins which destroy cellular barriers in the lungs, making them more permeable to allergens which can bring on asthmatic attacks. The trigger for these proteins seems to be nitrogen trichloride, a gas released in the interaction between chlorine and ammonia or ammonium compounds from urine, sweat, and other organic sources. More disturbing still, the researchers found that children who swam most frequently had protein levels similar to those found in regular smokers. The study concluded that regular swimming in chlorinated pools by young children resulted in an increased risk of developing asthma. The authors also suspect a link to the rising incidence of childhood asthma and allergic diseases found in industrialized nations.

Convincing your public pool to give up chlorine might not be easy either. Currently, 28 states require public pools to use sanitation equipment that meets the National Sanitation Foundation's NSF/ANSI Standard 50, which sets performance, disinfection efficacy, durability and safety criteria for pool and spa equipment. The standard doesn't currently cover disinfection chemicals, and in order to meet it, NSF-listed products, such as ozonators, ion generators and ultraviolet systems (all of which kill bacteria), generally have to be used in conjunction with a certain amount of either chlorine or bromine because they don't kill enough bacteria when used independently. Like chlorine, bromine can cause respiratory irritation, and according to research done in the U.K., skin irritation was more common in brominated pools than in chlorinated pools. If used with ozonators, the Environmental Protection Agency states that ozone can react with bromide, the active form of bromine, to form bromate, designated by IARC as a possible human carcinogen.

Since state regulations don't always apply to residential pools, you have some flexibility with the equipment you use at home. UV systems can be bolstered by hydrogen peroxide, and some disinfection systems incorporate potassium iodine, a much less irritating chemical. However, potassium iodine has to be combined with an oxidizer to react with debris and bacteria, and generally, the oxidizer used is chlorine.

There are some other chemical-free systems available for use in residential pools. However, be aware that an improperly sanitized pool can leave you susceptible to bacteria such as Cryptosporidium, Giardia and even E. coli, and that the effectiveness of chemical-free systems to kill these bacteria has not yet been assured by an independent third party, such as Consumer Reports or the NSF. Due to the lack of reliable third-party safety verifications, The Green Guide is unable to make recommendations for individual products. Therefore, ask the advice of your pool products salesperson about which completely chlorine-free products fit your individual pool needs.

Some suggestions for healthier pool maintenance and swimming:

• Avoid chlorinator tablets - they can produce high concentrations of chlorine that increase the risk of adverse health effects.

• Do not over-chlorinate, and test your water frequently to maintain desired level.

• Ozonators help reduce the concentrations of chlorine needed to keep the pool sanitary, and result in fewer reports of respiratory distress among swimmers. However, an Environmental Health Perspectives article reports that ozonators do produce bromate, a possible human carcinogen.

• Chlorine-free pool maintenance systems exist. While at present, their effectiveness does not seem to be assured by Consumer Reports or the Consumer Product Safety Commission, ask the advice of your pool products salesperson should you wish to consider one of the many chlorine-free options available.

• Do your best to reduce the organic matter in your pool. Use covers, remove leaves and dead insects frequently, etc.

• Swim in outdoor pools, or in indoor pools that have excellent ventilation. Indoor pools and poor ventilation seem to produce more adverse effects.

• Don't swim in highly chlorinated pools every day - if you do so, you risk build up of trihalomethanes and chlorine/chlorine by-products. As these substances do not bioaccumulate, swimming intermittently gives your body a chance to lighten your load.

• If you swim vigorously, you increase your chances of absorbing trihalomethanes and your chances of developing respiratory problems. Children, who breathe proportionately more air for their size than adults, also are at increased risk of unsafe exposure to chlorine and chlorine by-products. It's especially important for children and vigorous swimmers to exercise the above precautions.

• Reduce your overall exposure to chlorine and chlorine by-products by keeping your drinking water in a pitcher (which allows some products to evaporate) and by using filters on your drinking water tap and on your showerhead. Consult The Green Guide's product report on water filters for shopping suggestions.

Resource:

The National Sanitation Foundation (www.nsf.org) provides certification on pools, hot tubs and spas and on water purification systems. oem.bmjjournals.com/cgi/content/full/60/6/385

Sources:

Bernard, A. et al. "Lung hyperpermeability and asthma prevalence in schoolchildren: unexpected associations with the attendance at indoor chlorinated swimming pools." Occupational and Environmental Medicine, 2003; 60, 385-394. oem.bmjjournals.com/cgi/content/full/60/6/385

Lindstrom, A.B., Pleil, J.D., & Berkoff, D.C. (1997). "Alveolar breathe sampling and analysis to assess trihalomethane exposures during competitive swimming training." Environmental Health Perspectives, 105(6), 636-642.

Motavalli, Jim. "Swimming Upstream: New Products Fight the Backyard Pool's Chlorine Addiction." E Magazine, May-June 1998. www.emagazine.com/may-june_1998/0598gl_ecohome.html

Rushall, Brent S. "Chlorine Toxicity: A Matter That Should Be Of Concern To All Swimmers, Coaches, and Parents." www-rohan.sdsu.edu/dept/coachsci/swimming/chlorine/chlorine.htm.

Tibbetts, John. "What's in the Water: The Disinfectant Dilemma." Environmental Health Perspectives, Vol. 103, No. 1 (January 1995). ehpnet1.niehs.nih.gov/docs/1995/103-1/focus1.html