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. New research recently published in the Environmental Science and Technology sheds light on why fecal contamination affects sand more than water.

University of Hawaiʻi at Mānoa Associate Professor of Civil and Environmental Engineering Tao Yan and PhD student Qian Zhang researched why in the past decade, scientists have been finding fecal bacteria in beach sand at levels 10 to 100 times higher than in nearby seawater.

Researchers created microcosms of beach sand and seawater contaminated with sewage in a lab to see how the overall bacterial populations, including fecal dwellers responsible for causing illness, would change over time.

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 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.”

The Hawaiʻi State Department of Health provided additional funding for the project.

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The decay of fecal indicator bacteria and the change of microbial community structure were slower in beach sand than in seawater. Photo credit: ACS

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