Beach goers in the past have been warned multiple times about flesh-eating bacteria and scary shark attacks – now it seems like we’re not even safe sitting on the sand at the seashore! Studies done with water and sand from Hawaiian beaches found a “higher abundance” of bacteria indicating fecal contamination – bugs such as E. coli, for example – in the sand than in the water. The study, published online recently in the journal Environmental Science and Technology, discovered that fecal bacteria levels in beach sand may be 10 to 100 times higher than in adjacent seawater.
In fact, “waste water-contaminated marine beach sand may act as a chronic source of waste water bacteria to the beach seawater,” writes a team led by Tao Yan of the University of Hawaii at Manoa.
Public health experts have long known that waste water 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 stomach ache, diarrhea and rashes, Yan’s team noted.
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.
They obtained their sand samples from Kualoa Beach on the island of Oahu, at about a foot and a half above the high-tide line.
In the lab simulations, Yan’s team found that bacteria tended to decay much slower in the beach sand than in the water. This could explain why more fecal bacteria is typically found on the beaches than in the nearby water, the researchers said.
According to the researchers, 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: “Beach sand needs to be considered carefully in assessing its impact on water quality monitoring and public health.””