# News Release

+----------------+-------------------+--------------+-----------------+
| Dec. 6, 2004   | Donald Stoeckel   | 614-430-7780 | <sto            |
|                | (tech. lead)      |              | eckel@usgs.gov> |
|                |                   | 304-347-5130 |                 |
|                | Melvin Mathes     |              | <mvm            |
|                | (proj. lead)      | 804-261-2636 | athes@usgs.gov> |
|                |                   |              |                 |
|                | Ken Hyer          |              | <ke             |
|                |                   |              | nhyer@usgs.gov> |
+----------------+-------------------+--------------+-----------------+

Study Urges Caution in Contaminant Source Tracking

**Note to Editors:** The report, "Comparison of seven protocols to
identify fecal contamination sources using *Escherichia coli,*" is
available to reporters from the contacts above.

When a community finds that water it relies on for drinking or
recreation contains *E. coli* (*Escherichia coli*), a bacterium found in
the feces of warm-blooded animals that indicates fecal contamination,
residents and officials naturally want to find the cause and fix it \--
quickly. But several testing methods using *E. coli* to identify the
sources of fecal contamination were less accurate in field application
than previously reported, according to a recent U.S. Geological Survey
(USGS) report published in the journal Environmental Science and
Technology.

The USGS-led study, done in cooperation with state and local government
agencies and several universities and affiliated consultants, was among
the first to test the accuracy of microbial source tracking methods
against samples of known origin, called "challenge isolates." Scientists
compared the accuracy of several source tracking tools in classifying
*E. coli* strains to various sources (humans, dogs, geese, deer, horses,
pigs, cows, and chickens).

When researchers sent *E. coli* challenge isolates (the sources of which
were unknown to those conducting the tests) for testing, many isolates
either remained unclassified or were classified to incorrect sources. In
all, fewer than 30 percent of challenge isolates were classified to the
correct source-animal species by any method.

"When people are faced with contaminated drinking water, they want a
rapid response and remediation," said Don Stoeckel, USGS technical lead
for the project. "This could involve repairing sewers, modifying
agricultural practices, or other efforts that are costly. The ability to
trace back to the source is crucial in making sure the response actually
fixes the problem."

Within the last five years, state governments have begun using microbial
source tracking methods with *E. coli* bacteria to help manage bacteria
loads to streams. Various commercial firms offer source tracking
services to clients around the country.

"All too often, results of these analyses are offered without enough
validation of accuracy," Stoeckel explained. "Source tracking study
results should always be supported by quality control data.
Interpretation of the results can be supported by multiple lines of
evidence, such as land use data and presence of wastewater chemicals
such as caffeine, when pointing to sources of contamination. Both the
client and the analyzing laboratory have a part in making sure
interpretations are accurate."

Prior source tracking research reports cite accuracy ranges from 60--90
percent for various source tracking methods. The authors of the USGS
study attribute the discrepancy between the 60--90 accuracy rates and
the 20--30 accuracy rates they reported to a number of other factors:

-   Different bacteria may be present in animal guts in different
    seasons; in the USGS study, challenge isolates were collected 9
    months after the reference feces were collected;

-   There may be too many strains of *E. coli* bacteria in each animal
    species for effective application with small reference libraries,
    such as the 900 reference strains in the USGS study. At a cost of
    \$10 to \$100 to analyze one reference strain, however, building
    large source libraries gets expensive rather quickly.

-   *E. coli* strains may not be truly specific to one animal source.
    Some *E. coli* strains have been found in more than one animal
    source, such as when animals live in close proximity with one
    another, though no evidence to support this premise was found in the
    USGS study.

Further research may lead to improvements in current source tracking
methods or development of better methods. For the immediate future,
researchers and end users would be prudent to use caution and to
incorporate quality-control measures to validate the accuracy of source
tracking results.

This news release can be viewed online at
<http://wv.usgs.gov/press.html>

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