For longer versions of these and other
Environment stories, visit www.sciencenews.org
Cracked sewers leak fecal germs
By Janet Raloff
New studies in California and Wisconsin reveal a dirty little secret: Out of
sight, many urban sewer pipes are failing, allowing germ-ridden filth to bleed
into storm drains. These drains, which
channel their contents into streams and
coastal waters, are designed to collect
fairly clean rainwater and runoff from
watered lawns. Yet raw sewage at times
constituted 17 percent of one local storm
drain’s flow, report Patricia Ann Holden
of the University of California, Santa
Barbara and her colleagues.
“We found the same thing,” says
Sandra McLellan of the University of
Wisconsin–Milwaukee. In the August
Water Research, her group reports find-
ing a bacterial indicator of human feces
in samples from all 45 storm water
outflows in the Milwaukee area that the
researchers monitored over four years.
The data show that sewage contamina-
tion “is nearly ubiquitous in the urban
environment,” McLellan says.
New studies find sewage contamination
is widespread. Green dye exiting this
Wisconsin storm drain was originally
added to an upstream sewer pipe.
a fluorescing dye to sewage. Using an
automated sensor, the researchers looked
for the telltale dye in nearby storm drains.
In one system, the dye showed up in
storm drains within a half hour. In a second, it took between t wo and 74 hours for
the dye to emerge in storm water. In both
instances, two other bacterial indicators
of human feces accompanied the dye,
the California scientists report online
July 25 in Environmental Science & Technology. In a third system, where the
apparently leaky sewage pipes lay below
storm drains, no dye or germs appeared
to be wicked up into storm water pipes.
The California study “definitively
links leaky sewers to problems with
water contamination of rivers, oceans
and lakes,” says Marc Edwards of Virginia Tech in Blacksburg. “It informs our
understanding of how decaying water
infrastructure can threaten human
health and the environment, and helps
in prioritizing investment to mitigate
these risks.”
Spilled BP crude may not
have provided balanced diet
noses. To the scientists’ surprise, local
bacteria pigged out, more than quintu-
pling their normal daily intake with no
increase in their mass. The researchers
describe their findings online August 3
in Environmental Research Letters.
Bacteria gobbled
oil, didn’t grow
The Woods Hole researchers sampled
water from five sites inside the surface
slick and seven more upwind.
They dumped water from six
of the sites into gas-tight jars
that contained a new kind of
molecular sensor. Shining
light on this sensor induced
a fluorescent readout of
the water’s oxygen content.
Because bacteria use fairly
predictable amounts of oxygen when they break down
oil, oxygen depletion offered
an indirect measure of the
bugs’ dining rate.
—and especially the gorging diners
inside the slick — suffered from a shortfall of phosphorus, a nutrient essential
for growth. Offering affected bacteria
extra phosphorus greatly boosted their
feeding rate and their proliferation. But
even without the dietary aid, the team
found, it appeared Gulf microbes were
breaking down oil at an
unprecedented rate.
Enzyme measurements
confirmed that Gulf bacteria
Scientists used this
laser-based sys-
tem to monitor the
eating habits of
microbes in the Gulf.
The new findings “are
very interesting but not
totally surprising,” says
Terry Hazen of Lawrence
Berkeley National Laboratory in California. Although
oil degradation in the slick
proceeded faster than had
been expected, he says that
the rapid rate may reflect
the bugs’ adaptation over
millions of years to the large
number of natural oil seeps
in the Gulf of Mexico.
By Janet Raloff
When the Deepwater Horizon accident
spewed millions of barrels of oil into the
Gulf of Mexico last year, surface bacteria launched into a feeding frenzy, a new
study finds. But microbes that gobbled
up the surface oil did so without increasing their numbers or gaining weight.
Waters in much of the Gulf are fairly
mineral-poor, at least in terms of what
microbes need to flourish, says chemical
oceanographer Benjamin Van Mooy of
the Woods Hole Oceanographic Institution in Massachusetts. He and his team
expected that microbes encountering
the oil slick would turn up their figurative
www.sciencenews.org
September 10, 2011 | SCIENCE NEWS | 13
