Just when you thought it was safer to stay out of the water.

Microbes that result in beach closures and health advisories when detected at unsafe levels in the ocean also have been detected in the sand, according to a recent study by a team of Stanford scientists.

Published in the July 1 issue of Environmental Science and Technology, the study found that sand at beaches all along the California coast contained some level of fecal indicator bacteria. Moreover, when the researchers looked closely at the sand quality at a popular beach in Monterey, Calif., they found evidence of human waste-raising doubt about the commonly held belief that some fecal indictor bacteria occur naturally in the sand and are therefore benign.

The team was led by Alexandria Boehm, assistant professor of civil and environmental engineering at Stanford, and included Kevan Yamahara, Blythe Layton and Alyson Santoro, all graduate students in Boehm's lab and co-authors of the study. They collected samples of sand at 55 beaches between Mexico and Oregon and tested for fecal indicator bacteria in the lab and out in the field.

They found that 91 percent of the beaches in the study had detectable levels of enterococci and that 62 percent of them had traces of E. coli. Swimming in water with high levels of those bacteria can cause a number of reactions, such as skin rashes or ear infections. According to the Natural Resources Defense Council (NRDC), if ingested or absorbed through an open wound, pathogens in the water can trigger more severe ailments, including dysentery and hepatitis.

"Contaminated beach sands can actually act as bacteria sources," said Boehm, the Clare Booth Luce Assistant Professor in the Department of Civil and Environmental Engineering. "It means that the polluted sand is probably going to act as a source of fecal indicator bacteria to coastal waters-and will impact beach closures and advisories."

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Contact: Michael Pea
michael.pena@stanford.edu
650-725-4275
Stanford University
7-Aug-2007