Let water sit around for 24 hours — stagnating in an old tire, say, or in a birdbath in the backyard — and some pretty nasty things can start breeding in it. After Mt. St. Helen’s erupted in Washington State in 1980, newly formed oxygen-deprived pools became breeding grounds for Legionnaires’ disease. Then there’s cholera, typhoid, dysentery, and other illnesses that can be contracted from untreated bathing and drinking water. Yet, while swimming in a bacteria- and pathogen-filled pool poses clear health threats, chlorine is not a risk-free solution.
What lies beneath?
Some very harmful substances — dioxins and furans, for example, and also trihalomethanes — can form when chlorine products come in contact with carbon-containing organic matter, such as leaves and dirt. Dioxins and furans are extremely toxic and are among the “dirty dozen” chemicals targeted for elimination in the 2001 Convention on Persistent Organic Pollutants. Some studies suggest that trihalomethanes, which include the carcinogen chloroform, may cause miscarriages, birth defects, and bladder and rectal cancers.
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