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article imageGoing to the beach? Watch out for fecal contamination in the sand

By Karen Graham     Jul 15, 2015 in Science
Summer weather means trips to the beach, all across America, whether you're headed to a popular ocean spot or the lake, you might want to check on the water and sand quality first.
Many beach-goers have already seen the signs popping up along their favorite beaches this summer, warning of fecal contamination levels being too high for safe swimming. While many people ignore the signs, at their own risk, others heed the warning, opting to spread their blankets and beach towels to take in the sun.
But if the water is unsafe, just how safe is the sand? A new study published on Wednesday may surprise everyone. Swimming or wading in sewage contaminated coastal waters can lead to stomach aches. diarrhea and rashes in those who accidentally swallow some of the water, or even come into contact with it.
But for the past 10 years, scientists have been finding levels of fecal bacteria in beach sand 10 to 100 times higher than levels in the adjacent sea or lake waters. Researchers at the University of Hawaii at Manoa set out to find out why this was happening.
The scientists created colonies of seawater and sand microorganisms to study the kinetics of the bacteria and the change in microbial communities in beach sand and seawater. It may not be so surprising when you think about it, but the researchers found that microbial colonies decayed much slower in the sand than they did in seawater.
Graphic showing difference in decay rates of bacteria on sand and in seawater.
Graphic showing difference in decay rates of bacteria on sand and in seawater.
Qian Zhang et. al.
This discovery helps in shedding light on why fecal contamination in seawater along coastal beaches tends to drop quickly after continued wave motion but remains high in the sand along the same waterline. Several coliform bacteria were used in the study, including Escherichia coli, enterococci, and Clostridium perfringens.
The potential sources of fecal bacteria in seawater and in lakes
Sometimes the sources of fecal contamination along beaches is not known. This can be due to changing wind, wave, and weather patterns. The origin of the fecal contamination also needs to be taken into consideration. For example, heavy rains can create flooding and heavy runoff of animal waste along agricultural lands pasturing livestock.
Other sources of fecal contamination include failing or leaking septic systems, sewage system breakages and overflows, improper diaper disposal, swimmer accidents and the improper dumping of boat waste. Of course, any of these sources would lead to very high levels of fecal contamination in lakes, ponds or even swimming pools.
Radio Island beach, in Beaufort, North Carolina was tested on Monday this week. The inspector, JD Potts, found the levels of the bacteria, enterococcus to be 16 times higher than what is considered a safe level for swimming. As manager of the North Carolina Division of Marine Fisheries’ recreational water quality program, Potts tests water in coastal swimming spots, including beaches, sounds, bays and rivers.
Potts says the contamination can come from a variety of sources, including pets, wildlife, and the sources already listed above. In North Carolina, alone, inspectors have already posted 13 advisories in 10 swimming spots this year, and the season is just getting into full swing.
Microbiological Source Tracking (MST) used to test for fecal contamination
Basically, MST is a method of identifying a particular source of fecal contamination in water or beach sand. There are several methods in use today, but they all generally use a fecal indicator bacteria, such as Escherichia coli (E.coli) or Enterococci, to measure the levels of contamination.
Graphic showing overview of MST method.
Graphic showing overview of MST method.
Michigan State University
The basic premise behind using MST tracking is that fecal bacteria from a particular host, such as animals, birds or humans, will exhibit certain characteristics particular to the host. This information allows scientists to pinpoint the source of the contamination. Most of these "target genes" can be used to "fingerprint" the mammal, human or bird responsible for the contamination.
The study was published in the journal Environmental Science and Technology on June 30, 2015, titled: "Differential Decay of Wastewater Bacteria and Change of Microbial Communities in Beach Sand and Seawater Microcosms."
More about Beaches, Sharks, Fecal contamination, coliform bacteria, Water testing
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