Bacteria at the beach? They’re not always a sign of contamination
UCLA researchers have found that the wet sand of some enclosed, family-friendly beaches in Southern California may harbor higher levels of certain bacteria -- and by extension certain pathogens -- than unsheltered beaches with better water circulation. A team led by Jennifer Jay, assistant professor of environmental engineering, found higher levels of Escherichia coli and enterococci at two sheltered beaches (the enclosed portion of Cabrillo Beach in San Pedro, and Mother’s Beach in Marina del Rey) than at 11 open beaches in Santa Monica Bay.
Janet Cromley
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The waters of Southern California beaches are tested -- sometimes daily -- by dozens of city and county agencies as well as volunteer organizations. Groups test for total and fecal coliform bacteria, enterococci and sometimes E. coli.
These bacteria signal the possible presence of human fecal matter, which can harbor bacterial, viral and parasitic pathogens that cause gastrointestinal illness, eye and ear infections and skin rashes.
Finding high levels of so-called indicator bacteria in the sand of enclosed beaches isn’t all that surprising because calm beaches don’t have the benefit of constant flushing of clean water and sand renewal, notes Mitzy Taggart, a scientist for Heal the Bay.
The most family-friendly beaches are often the ones with the poorest water quality, she says.
High levels of pathogens in the sand probably would pose the greatest risk to small children, who tend to play in sand and get it in their mouths.
But the presence of indicator bacteria in sand doesn’t necessarily mean a stretch of beach is contaminated with human waste. The bacteria could have come from other sources such as droppings from birds, feral animals and pets.
It’s also possible that the indicator bacteria are multiplying, without the more harmful pathogens present. These bacteria can multiply in wet sand, fed by kelp and other organic material that accumulate at the tide line, says Charles McGee, a microbiologist and lab supervisor for the Orange County Sanitation District.
If that’s what’s happening at the enclosed beaches, “then we could be getting an overestimation of the risk,” Jay says.
Whether exposure to human fecal matter -- which gets into water from sewer overflows, diaper-wearing infants and even swimmers -- will cause illness depends on several factors, including the amount of exposure; how much of a particular pathogen is absorbed through the nose, ears, mouth or broken skin; and the general health of the person exposed.
Generally, gastrointestinal infections that are picked up at the beach are short-term. Symptoms appear within the first few days, and the illness runs its course within 10 days.
Despite concerns surrounding some Southern California beaches, health experts say that most are clean and safe places to swim and sunbathe. For information on water quality, check the beach report card at www.healthebay.org.
