September 12, 2007
California ‘Sand Pollution’ Intrigues Researchers
By Suzanne Bohan
Here's a term you may start to hear more often: sand pollution.No one knows exactly what's causing it, but scientists do know that beaches often contain high levels of bacteria linked to the presence of harmful pathogens.
Along the California coast, the majority of 55 beaches tested had detectable levels of these bacterial warning flags, enterococci and E. coli, according to a recent study from a Stanford University research team. Ninety-one percent of the beaches tested positive for enterococci, while 62 percent had measurable amounts of E. coli.
While the particular strains of these microbes aren't usually harmful to humans, they do signal the possible presence of more harmful microbes like viruses or other bacteria that do cause illnesses.
The study, published in the July 1 issue of Environmental Science & Technology, is the most extensive one yet assessing sand pollution along the California coast.
It also provides evidence that bacteria permeating wet sands are carried away by waves, increasing bacteria levels in the adjacent waters. Dry sands above the tide line have low levels of bacteria, researchers noted.
"We know that (bacteria) can leave the sand and enter water," said Alexandria Boehm, assistant professor of civil and environmental engineering at Stanford, who led the study team.
Along the nearby coastline, Bean Hollow State Beach, near Pescadero, had the highest levels of the three San Mateo County beaches tested, said Boehm. In Santa Cruz County, Cowells Beach has the highest numbers, she added.
The Bean Hollow figures didn't surprise Gary Strachan, supervising ranger for Ano Nuevo State Reserve, since dogs are permitted at the beach. "People don't always pick up after themselves," he said, referring to the dog piles routinely found along the park's shore.
Ray Stearns, a spokesman for the California Department of Parks and Recreation, which manages Bean Hollow, added that beaches are the last terrestrial repository for pollution from urban runoff, creeks and storm drains. "We're the last stop for it on our beaches," he said.
But before you retire the beach volleyball set and scratch plans to build a sandcastle with the kids, keep in mind that scientists are still investigating the meaning of this growing body of data.
"I wouldn't want to discourage people from doing what they do, because the risk is really unknown," said Jenny Jay, a professor of environmental engineering at the University of California, Los Angeles, who studies sand pollution.
The health effects of exposure to pathogens in water are well known. Between 2003 and 2004, 2,698 people were reported as sickened by microbes found in recreational waters, according to the U.S. Centers for Disease Control and Prevention. But nothing is yet known about the health effects of exposure to bacterial-laced sands. Jay, however, said she's participating in the first study to assess this health risk. The research is being conducted on Catalina Island as part of a broader study of the beach environment, and is expected to conclude this year, she said.
Awareness of sand pollution hit the radar in 1994, when researchers found that levels of these "indicator bacteria" were far higher in wet sand, compared with the adjacent water, according to the Clean Beaches Council. A 2003 study from the U.S. Geological Survey found the levels were five to 10 times higher along the shore than in water.
But the question for scientists is whether these bacteria just grow more vigorously in the hospitable environment of moist sediment, compared with open water. Or do they signal that sandy beaches actually harbor high levels of the pathogens that come from human and animal waste?
"It could be these harmless guys are replicating," said Jay. "Or it could indicate that pathogens also exist."
If these bacteria simply grow more easily in sand, it means beach managers need to rethink the way they test for unsafe swimming conditions, Boehm pointed out. Between 2002 and 2003, beach waters and other recreational swimming areas were closed a combined 18,000 times due to high levels of enterococci and E. coli found in the waters.
But if enterococci levels exceeding state limits, for example, are due to high rates of replication and don't actually indicate the presence of other harmful pathogens, then some of those beach closures may be unnecessary.
If the bacteria in the sand, however, do come from fecal matter and other pollution sources, it ultimately may be necessary to test sand as well as water to protect human health, researchers point out.
Boehm's research found that small, sheltered beaches in developed areas and with streams or storm drains -- which may carry pollution - - had the highest levels of enterococci, indicating that the bacteria in those beaches came from human sources.
Boehm added that she's received a $400,000 four-year grant from the National Science Foundation to further study the sources of bacteria in sand.
Parents often prefer to take children to these sheltered beaches, researchers add, since they have fewer undertows and gentler waves.
Jay, with UCLA, said she brings her 3-year-old twins to the beach to play in the sand. But she added that, to be on the safe side, she didn't let them dig in the wet sand of one Southern California beach she knew had high levels of bacteria.
"It's true," she said, adding that her main precaution is getting the children to wash their hands after a visit to the beach.
For more information, read the "2005 State of the Beach Report: Bacteria and Sand" from the Clean Beaches Council. You can find the report at http://www.cleanbeaches.org/mediacenter.
Contact Suzanne Bohan at [email protected] or 650-348- 4324.
Originally published by Suzanne Bohan, STAFF WRITER.