People heading for a day at the beach in Southern California may have more to worry about than sunscreen, suggests a new study by researchers at the UCLA Henry Samueli School of Engineering and Applied Science.
The study shows that bacteria known as Escerichia coli and enterococci are prevalent in the top layer of sand at some of the area’s most popular beaches, even when the surrounding ocean water tests “clean.”
UCLA civil and environmental engineering professor Jennifer Jay and graduate researcher Christine Lee conducted a survey of beaches in Santa Monica Bay from Redondo Beach to Malibu.
Their research study — scheduled to be published in an upcoming issue of the journal Water Research — shows that while the water bacteria levels at area beaches may meet state health standards, the sand itself may act as a bacteria source.
However, because health standards for beach sediments have not been developed, there is no strict standard to evaluate exactly how much of a health risk these bacteria actually pose.
“The survival of these ‘indictor bacteria’ organisms in sand points to the persistence of other disease-causing organisms in the sand, which could be very significant,” Jay said. “But we don’t yet have enough data to know how significant. More research needs to be done in this area.
“What this study ultimately shows is the importance of monitoring bacteria in the sand as well as the water, particularly at enclosed recreational beaches,” Jay said.
Bacteria were found, the study says, in their highest concentrations in the sand of enclosed beaches often favored by parents with toddlers.
Parents favor enclosed beaches because of the lack of surf and because the coastline is more protected.
Usually associated with feces, both Escerichia coli and enterococci bacteria levels are used routinely to determine the quality of water at recreational beaches, and both are used as indicators of the possible presence of other harmful microorganisms.
But while water quality at local beaches is monitored on a daily basis by local city officials, the microbial quality of beach sand is often overlooked.
“Southern Californians are aware of swimming advisories and beach closings due to contamination of the water,” Jay said. “But what is startling about our findings is that even when the water shows low bacteria levels, there are still high levels of bacteria that persist in the sand.
“This is particularly relevant when we are talking about sheltered beaches such as Mothers Beach [in Marina del Rey] and the enclosed part of Cabrillo Beach [in San Pedro], for example, which appear to be more conductive to the persistence of these bacteria.
“The levels of enterococci were approximately 1,000 times higher than the levels observed at the beaches open to the ocean.”
High levels of bacteria were also found at Santa Monica State Beach near Santa Monica Pier.
The beaches tested by UCLA Engineering’s study include Santa Monica State Beach (north and south), Dockweiler Beach in Playa del Rey, Venice Beach, Mothers Beach (enclosed) in Marina del Rey, Surfrider Beach and Topanga State Beach in Malibu, Will Rogers State Beach in the Pacific Palisades, Manhattan Beach, Redondo Beach, and Cabrillo (open and enclosed portions).
“Due to their enclosed nature, ‘pocket’ or enclosed beaches show the highest levels of bacteria present in the sand,” Jay said.
“These more enclosed locations are, for good reason, popular with families. Children tend to put things in their mouths, including sand. That concerns me.”
She and her researchers are now working on a second study that will focus on the persistence of viruses in beach sediments.