“No swimming” signs have already popped up this summer along coastlines where fecal bacteria have invaded otherwise inviting waters. Some vacationers ignore the signs while others resign themselves to tanning and playing on the beach. But should those avoiding the water be wary of the sand, too? New research investigates reasons why this could be.
The new research recently published in the American Chemical Society (ACS) journal Environmental Science and Technology sheds light on why fecal contamination affects sand more than water.
Sewage-contaminated coastal waters can lead to stomach aches, diarrhea and rashes for those who accidentally swallow harmful microbes or come into contact with them.
“In an Italian study, a significant correlation was found between contamination of beaches and contamination of adjacent seawaters, although the sand generally had higher bacterial counts than the water. A similar tendency was found at Barcelona beaches; in contrast to the Italian study, however, the level of contamination was not significantly different between sand and seawater.”
But over the past decade, scientists have been finding fecal bacteria in beach sand at levels 10 to 100 times higher than in nearby seawater. The researchers wanted to find out why.
In the lab, researchers created microcosms of beach sand and seawater contaminated with sewage to see how the overall bacterial populations, including fecal dwellers responsible for causing illness, would change over time.
“Cultivation-based methods showed that common fecal indicator bacteria (FIBs; Escherichia coli, enterococci, and Clostridium perfringens) exhibited biphasic decay patterns in all microcosms. Enterococci and C. perfringens, but not E. coli, showed significantly smaller decay rates in beach sand than in seawater,” said in the paper.
They found that microbial communities tended to decay much slower in the simulated beach sand environment than in the water, which could help explain why more fecal bacteria are found on sandy beaches affected by waste water pollution than in the waves.
“For a beach, the sand is as important as the water, but our monitoring efforts have been placed almost exclusively on the latter,” said Tao Yan.
“Results of this study support the need for a holistic beach management approach that includes sand, which can help further advance our goal of public health protection.”
