Fecal microorganisms inhabit sandy beaches of Florida

May 13, 2008

Traditionally, the cleanliness of a beach is monitored by sampling the bathing water a few meters from shore. But since sand is an effective filter, it follows that fecal bacteria (those from sewage) may be concentrated in the sand as the tide flows and ebbs.

Moreover, trapped bacteria are offered a large surface area for attachment, nourishment from nutrients in sand crevices, and protection from sunlight. These bacteria might be afforded greater survival opportunities and may even be nourished enough to replicate in the beach environment.

Dr. Andrew Rogerson, formally of the Oceanographic Center of Nova Southeastern University, Florida, headed an Environmental Protection Agency study to determine the levels of fecal-derived bacteria in Florida beach sand and look for health implications.

Early results showed that wet sand (in the intertidal zone) and dry sand above the intertidal zone had significantly more fecal bacteria than near-shore seawater. This lead to the question– do indicator bacteria survive longer in sand relative to open water" A series of laboratory experiments were conducted to answer this question and the results are presented in the May-June issue of Journal of Environmental Quality.

All the feces-derived bacteria (i.e. traditional indicators of sewage contamination) were capable of enhanced survival in sand and, more importantly, were capable of growth in the sand leading to much higher numbers. Conversely, in seawater the bacteria steadily decreased in number over time.

Results also showed a rapid drop off in bacterial numbers in bathing water sampled close to the sand compared with 5, 10 or 20 m from shore. This indicates that the shoreline water is affected by bacterial run-off from the sand.

This has implications for beach managers since the number of bacteria from feces (fecal bacteria) in the water is used to assess the presence of sewages. A high count of these ‘indicator bacteria’ would require the beach to be closed, an action with financial consequences in tourist rich regions such as Florida. Any bacteria washed from the sand complicates the interpretation of counts in the water and could lead to unnecessary beach closures. On the other hand, high numbers of fecal-derived bacteria growing in the sand could constitute an increased health risk.

The authors suggest that water quality managers should consider sampling water further from shore than is routinely practiced (say 10 m from the swash zone) to avoid the complications of bacteria being washed from sand. However, further studies are required to determine whether these higher counts pose a health hazard to bathers. The results of a beach questionnaire designed to look for incidences of illness after beach use were inconclusive.

View the abstract at jeq.scijournals.org/cgi/content/abstract/37/3/898 .

Source: Soil Science Society of America

Explore further: Acorn worm genome reveals gill origins of human pharynx (Update)

Related Stories

Mars will come to fear my botany powers

November 10, 2015

NASA seems to believe that making space habitable will require more finesse than Elon Musk's "let's nuke Mars" plan, and has funded a couple of synbio projects which seek to provide "the means to produce food, medical supplies ...

Super-slick material makes steel better, stronger, cleaner

October 20, 2015

Steel is ubiquitous in our daily lives. We cook in stainless steel skillets, ride steel subway cars over steel rails to our offices in steel-framed building. Steel screws hold together broken bones, steel braces straighten ...

Scientists puzzled by sand bacteria

June 29, 2006

U.S. scientists say bacteria forcing the closure of many beaches may not be coming from people, animals, or sewage -- but might be produced in the sand.

What science says about beach sand and stomach aches

August 11, 2009

By washing your hands after digging in beach sand, you could greatly reduce your risk of ingesting bacteria that could make you sick. In new research, scientists have determined that, although beach sand is a potential source ...

Recommended for you

Can Paris pledges avert severe climate change?

November 26, 2015

More than 190 countries are meeting in Paris next week to create a durable framework for addressing climate change and to implement a process to reduce greenhouse gases over time. A key part of this agreement would be the ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.