Heading to the beach this weekend? Read this first

beach_blogBeachgoers and sandcastle builders beware. A new study has found that when it comes to germs, the sandy shores of beaches may be more dangerous than the water itself.

Recently published in the journal Environmental Science & Technology , the study looked at water and sand from Hawaiian beaches and found a “higher abundance” of bacteria indicating fecal contamination—such as E. coli, for example— in the sand than in the water.

In fact, “wastewater-contaminated marine beach sand may act as a chronic source of wastewater bacteria to the beach seawater,” Tao Yan of the University of Hawaii at Manoa, said in a recent article.

Public health experts have long known that wastewater from sewage and other sources can contaminate seawater, some days necessitating beach closures. Swimmers who come into contact with or accidentally swallow fecal-contaminated water can suffer stomachache, diarrhea and rashes, Yan’s team noted.

However, the researchers also noted that over the past decade, scientists have been finding fecal bacteria levels in beach sand that are 10 to 100 times great than in adjacent seawater.

To find out why that’s the case, the Hawaii scientists created laboratory simulations of beaches and seawater contaminated with sewage to observe how overall bacterial populations —including fecal bacteria that cause illness — change over time.

The article states that the scientists obtained their sand samples from Kualoa Beach on the island of Oahu, at about a foot and a half above the high-tide line.

Then, in the lab simulations, Yan’s team found that bacteria tended to decay much slower in the beach sand compared to the water. This could explain why more fecal bacteria is typically found on the beaches than in the nearby water, the researchers said.

But why do illness-linked bacteria such as E. coli and enterococci linger longer in sand?

According to the article, wastewater bacteria can easily become embedded in “biofilms” within sand that “provide shelter” to bacteria. Sunlight can also deter bacteria growth, the scientists said, and sand provides these germs with some cover from sunlight, whereas shallow seawater does not.

The bottom line, according to Yan’s team is that “beach sand needs to be considered carefully in assessing its impact on water quality monitoring and public health.”

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