- Americans' love affair with their pets may be a major
cause of water pollution in urban areas, particularly following periods
of heavy rain.
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- That is one of the implications of an investigation into
the source of bacterial contamination in the streams and tributaries in
the Nashville area conducted by doctoral student Katherine D. Young and
Professor Edward L. Thackston in the civil and environmental engineering
department at Vanderbilt University. It is the latest in a series of studies
conducted in various parts of the country that suggest pet wastes may be
a significant cause of bacterial pollution.
-
- The research project, described in a paper published
in the December issue of the Journal of Environmental Engineering, measured
levels of fecal coliform bacteria in four neighborhoods in north Nashville.
The object of the study was to determine if septic systems could be the
cause of unexpectedly high bacterial levels that had been detected previously
in local streams and tributaries. Two of the Nashville neighborhoods that
the researchers studied were sewered and two relied on septic systems.
The researchers could not find any evidence of leaking septic or sewer
systems, but they did find high bacterial levels in runoff from streets
and lawns.
-
- "We can't say with absolute certainty that pets,
along with other urban wildlife, are the cause of this bacterial pollution,"
says Thackston, "but all the signs point in that direction."
-
- If pets and urban wildlife are indeed major sources of
water contamination in many cities, it raises an important public policy
issue, Thackston says. In urban areas, environmental regulators generally
assume that bacterial contamination comes from human wastes, such as leaky
sewers and septic tanks, rather than from animals. Many states and cities
are currently struggling to establish maximum daily loads for bacterial
pollutants in local streams. If the basic assumption about the cause of
this contamination is incorrect, then the decisions that they make are
likely to be inappropriate, Thackston argues. So he urges regulators to
do the additional testing required to differentiate between the two causes
of pollution so that they can make informed decisions on the matter.
-
- Animal wastes are not considered to be as dangerous as
human wastes, because the bacteria they contain are not as likely to attack
humans. However, exposure to animal feces can cause gastric distress and,
along with other organic wastes like grass clippings, leaves and garbage,
they can taint fresh streams and rivers, robbing them of oxygen and killing
aquatic life.
-
- Fecal coliform bacteria, the indicator of fecal matter
contamination used in state and federal water quality regulations, are
present in both human and animal waste; so, routine tests cannot tell the
difference between the two, Thackston explains. Animal wastes contain higher
levels of another bacteria, fecal streptococci. As a result, when the ratio
of coliform to streptococci bacteria is low, researchers consider it to
be a strong indication that the source is primarily animal rather than
human.
-
- In the case of the Nashville study, Thackston and Young
confirmed previous studies that found the coliform/streptococci ratios
in the Nashville runoff to be extremely low. The researchers also found
that bacterial levels in local runoff were 10 times higher in the sewered
areas than it was in the less heavily developed areas with septic tanks.
In fact, the researchers found that the higher the housing density in a
neighborhood, the higher the level of contamination. "And one of the
things associated with housing density is the number of pets per acre,"
Thackston says.
-
- Two factors contribute to the pet pollution problem,
the water pollution expert says. One is the sheer number of pets in urban
areas. "The density of pets in urban neighborhoods is far greater
than the number of similarly sized animals in a wild setting," he
points out.
-
- The second is the nature of the urban environment itself.
In the wild, animal droppings are generally held in place where they fall
by long grass or bushes. That allows them to decompose in place. By comparison,
streets, parking lots and even lawns are hard, flat surfaces. So animal
wastes deposited there are less likely to decompose and much more likely
to get washed into drains and ditches and carried into nearby streams.
-
- New methods have been developed to test for bacteria
that are unique to animal and human feces. Thackston's research group is
attempting to apply some of these techniques to local runoff in order to
provide more direct evidence for the source of the contamination, but they
have been hampered by lack of local rainfall. The Vanderbilt research is
consistent with a number of other studies:
-
- * Environmental Protection Agency studies conducted in
1983 and 1989 at the University of Michigan found that high levels of bacteria
were present in urban runoff, especially during and immediately after heavy
rains.
-
- * A 1995 study in Wilmington, N.C., found that the bacterial
levels in tidewater creeks in the area were positively correlated with
the urban density in the drainage areas.
-
- * An extensive 1996 study undertaken by the Boston Water
& Power Company attributed bacterial contamination in the storm drains
covering a 200-acre area of the city to dog feces.
-
- * In 1998 Mansour Samadpour, a microbiologist at the
University of Washington, applied a "microbial source tracking"
method that he developed to identify the source of bacterial contamination
that closed a swimming beach on Lake Washington. Although local officials
thought that leaky toilets at the beach might have been the source, Samadpour's
result implicated dogs, cats and wild birds. Note: This story has been
adapted from a news release issued by Vanderbilt University for journalists
and other members of the public. If you wish to quote from any part of
this story, please credit Vanderbilt University as the original source.
You may also wish to include the following link in any citation: http://www.sciencedaily.com/releases/1999/12/991206071651.htm
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