The Dirty Secret of Outdoor Exercise

Hidden Dangers

More threats await on the emerald grass of the golf course (pesticides and fertilizers) and the bucolic woodland trails you bike and hike (insecticides). Lakes, rivers, streams, and bays can be spiked with agricultural runoff from fertilizer and pesticide residues or industrial waste and sewage overflows. "Swimming in these conditions can cause gastrointestinal problems, diarrhea, skin rashes, ear and eye infections, even hepatitis," says Michelle Mehta, a representative for the Natural Resources Defense Council, a New York City-based nonprofit environmental action group.

In the United States the number of beach advisories and closures issued in 2008 because of pollution topped 20,000 for the fourth consecutive year. Even people who live near some of the nation's most pristine waterways are worried. "I'm concerned about potential sewage overflow after a rainstorm," says Kristan Drzewiecki, 39, a management consultant who regularly swims in Casco Bay, just offshore from her home on Peaks Island, Maine. Two summers ago the beach just across the bay from where she swims was closed for nine days as a result of high contamination levels. It hasn't stopped Kristan from getting her swim workout, but it's changed her attitude from enthusiastic to anxious. "I try to keep my mouth closed when I swim now," she says, acknowledging that this alone is probably not enough.

Of course, "none of this means you should stop exercising outdoors," Dr. Edelman says. "You simply need to be aware of pollution and do all you can to avoid it -- and not contribute to it yourself." For example, having to change her midday run to a walk inspired Brenda St. Hilaire to volunteer with an environmental group. "I joined Clean Water Action, signing petitions and donating," she says, referring to the 1.2 million-member grassroots organization that attacks the basic causes of water and air pollution. She hopes to be able to run outside again someday. Until then, "at least I feel I'm doing something to help solve the pollution problem."