Beach Pollution is worse during Full Moon and New Moon

[Guest guest]

03 Aug 2005

 

 

 

 

 

A new study of 60 beaches in Southern California suggests that water

pollution varies with the lunar cycle, reaching the highest levels

when tides are ebbing during the new and full moon. The findings

could help beachgoers and managers better assess the potential risk

of swimming.

 

The report appears in the Aug. 1 issue of the American Chemical

Society's journal Environmental Science & Technology. ACS is the

world's largest scientific society.

 

Coastal water quality is controlled by a number of complex physical

and biological factors, including tidal cycles and seasonal rainfall.

This complexity makes beach water monitoring difficult, with levels

of bacteria in a certain area changing in just a few minutes.

 

For the new study, the researchers examined monitoring data compiled

for beaches throughout Southern California, keeping track of tidal

patterns and analyzing them for concentrations of enterococci --

bacteria that allow scientists to estimate the risk of illness from

swimming in marine waters. " This is the largest array of beaches

examined at the same time for a similar pattern, " says Alexandria

Boehm, Ph.D., an environmental engineer at Stanford University and

lead author of the study.

 

She and her colleagues at the Southern California Coastal Water

Research Project found that in the full and new phases of the moon,

levels of enterococci were higher at the vast majority of the beaches

studied. Boehm found that during so-called " spring tides, " when water

levels vary the most between high and low tides, a beach is twice as

likely to be out of compliance with water quality standards. Spring

tides are exceptionally high or low tides that take place during the

full and new moons, but have nothing to do with the season of the

year.

 

The results are of immediate practical use to swimmers and beach

managers alike, according to Boehm. " The general public can use the

phase of the moon and the tide stage to assess the relative risk of

illness, " she says. " It is riskier to swim during spring-ebb tides

[receding tide] compared to all other tidal conditions. "

 

Beach managers can now use tides as they currently use rainfall to

assess warnings, Boehm suggests. When it rains, managers recommend

that swimmers not enter the water for three days. " They could also

suggest that during spring tides -- and especially spring-ebb tides --

water quality is more likely to be impaired, and those who are risk-

averse should avoid swimming, " Boehm says.

 

The results might also help managers identify potential sources of

pollution at beaches. " Most sources of enterococci at beaches are

unknown, " Boehm says. " Because we found tidal signals in enterococci

densities at beaches with no obvious point source, like storm drains

and creeks, this suggests that there is a widespread tidally forced

source of enterococci at beaches. "

 

Boehm suggests several candidates for this " mystery " source,

including beach sands, decaying plant material and polluted

groundwater. " Beach sands and wrack [piles of seaweed and animal

remains that wash ashore] have been shown at freshwater beaches to

harbor fecal indicator bacteria and even pathogenic bacteria, " Boehm

says. " Beach managers who want to improve water quality at their

beaches should investigate the potential of these sources to be

contributors of enterococci to marine waters. "

 

Boehm cautions that enterococci from beach sands and wrack may not

correlate with health risk the same way as enterococci from runoff or

sewage. " We just don't know for sure, since no one has done an

epidemiological study to connect human illness to enterococci from

non-point sources other than runoff, " Boehm says. " We need to do

additional work to understand the source of enterococci at all these

beaches. "

 

The American Chemical Society is a nonprofit organization, chartered

by the U.S. Congress, with an interdisciplinary membership of more

than 158,000 chemists and chemical engineers. It publishes numerous

scientific journals and databases, convenes major research

conferences and provides educational, science policy and career

programs in chemistry. Its main offices are in Washington, D.C., and

Columbus, Ohio.

 

-- Jason Gorss

 

The online version of the research paper cited above was initially

published June 15, 2005, on the journal's Web site. Journalists can

arrange access to this site by sending an e-mail to newsroom

or calling the contact person for this release.

 

Michael Bernstein

m_bermstein

202-872-6042

American Chemical Society

http://www.acs.org