4 Reasons for the 72-hour Beach Advisory


4 Reasons for the 72-hour Beach Advisory

What exactly happens in this 72-hour period that magically turns water that can give you diarrhea, an eye infection, bronchitis or worse into water safe for human contact?

Posted by Michelle Mowad (Editor) , November 15, 2013 at 12:31 PM
Patch file photo.
Patch file photo.

Written by Christina S. Johnson/California Sea Grant at Scripps Institution of Oceanography

Surfers know that they should stay out of the water for at least 72 hours after it rains to avoid getting sick.

This is especially true after a “first flush” storm, the first heavy rain of the season, when an accumulation of grit, grime and pathogens built up during the dry season are carried in runoff, storm drains and rivers to the beach, and perhaps your favorite surf spot.

“We’ve done the monitoring and we know bacteria counts spike after it rains and go back to normal, in general, in 72 hours,” said Keith Kezer, an environmental health specialist with San Diego County’s Beach and Bay Monitoring Program.

But what exactly happens in this 72-hour period that magically turns water that can give you diarrhea, an eye infection, bronchitis or worse into water safe for human contact?

Kezer listed four processes that naturally reduce “fecal indicator” bacteria counts, which when elevated trigger beach closures. We thought we’d share, as an interesting FYI, since the rainy season and the good surf will soon be upon us.

Here they are:

  1. Dilution. Harmful bacteria that are swept into coastal waters in a pulse of runoff are dispersed and diluted by ocean currents. “The solution to pollution is dilution” was the old adage. Notably, enclosed beaches, which are less exposed to ocean currents, may have high fecal indicator bacteria counts for 10 days after a rain, according to a recent UCLA study.
  2. Ultraviolet radiation. Sunlight kills a lot of bacteria.
  3. Seawater. Salt is also lethal to some microbes.
  4. Predation. Bacteria are part of the food chain and are grazed on by free-living protozoans and other microbes. It’s a microscopic jungle out there.

California Sea Grant is currently funding research that is looking to develop the next generation of water-quality testing technologies, including a better understanding of viral pollution, which is not currently monitored at beaches.

Below are two of our ongoing research projects, summarized with contact information for the lead investigators.

In-situ Detection of Indicator Organisms by Digitization and Concentration in Microfluidic Picoliter Droplets
R/CONT-219 Feb. 2013–Jan. 2014
Sindy Tang, SU, 650-723-5385, sindy@stanford.edu

The researcher has designed but not fully tested an intensely high-tech approach for monitoring low concentrations of pathogenic bacteria in water samples. In the method, water samples are mixed with probes that enzymes in bacteria convert to a fluorescent-colored product. Picoliter (trillionth-of-a-liter) droplets are formed from this mixture and the brightly colored drops are then counted to estimate bacterial concentrations. The key step in the approach is the ability to form the droplets, within which a single cell will have a very high effective concentration, on the order of 10^9 cfu/mL. Besides amplifying the pathogenic signal, the approach also reduces the assay time for detecting bacteria, which is critical for protecting public health. The main objective of this proof-of-concept project is to demonstrate the ability to form the droplets and count cells for the fecal indicator bacteria Escherichia coli and Enterococcus sp. The method’s accuracy will be verified for samples with known cell counts. The scientist will also characterize the rate at which color intensity builds in “incubating” droplets, as a function of droplet size, to identify an optimal drop size and assay time for the bacteria. The enzyme-substrate probe technology to be employed in this project has been approved and is expected to become adopted by the EPA. Outcomes from this project will further efforts to quantitatively measure low concentrations of water-borne pathogens through a technique that “packages” the EPA method in picoliter containers.

Noroviruses in Coastal Waters: Implications for Seafood Cultivation and Human
R/CONT-216 Feb. 2012–Jan. 2014
Stefan Wuertz, UCD, 530-754-6407, swuertz@ucdavis.edu
Karen Shapiro, UCD, 530-754-6144, kshapiro@ucdavis.edu
Woutrina Miller, UCD, 530-219-1369, wamiller@ucdavis.edu

Fragments of single-stranded RNA known as noroviruses are the leading cause of food-borne
disease outbreaks in United States, according to the Centers for Disease Control. Though
outbreaks usually occur in small areas of high population density, such as nursing homes or
cruise ships, the scientists leading this project have detected the virus in all types of freshwater discharges, including rural runoff. This project will investigate whether livestock or other animals may be capable of carrying and spreading the viruses. Researchers will also test whether noroviruses are present in coastal waters of Central California at concentrations that pose a human health risk. Field work will focus on detecting the viruses in seawater and suspended aggregates formed in estuaries and the marine environment. Also of interest is the degree to which local mussels accumulate the viruses and their correlation with concentrations of zoonotic pathogens (e.g., Cryptosporidium, Giardia, and Salmonella) and fecal indicator bacteria. The anticipated outcome of the project is an improved assessment of the presence, or absence, of noroviruses along Central California, and a first estimate of the level of risk the pathogens pose to those who consume raw shellfish grown or harvested locally.

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