Study Urges Caution in Contaminant Source Tracking

["Shannon Briggs" <briggssl@michigan.gov>]

FYI:
E. coli Tests Only 20-30% Accurate - Dec 6: A recent U.S. Geological
Survey (USGS) report published in the journal Environmental Science and
Technology indicates that several testing methods using E. coli
(Escherichia coli, a bacterium found in the feces of warm-blooded
animals that indicates fecal contamination) to identify the sources of
fecal contamination were less accurate in field application than
previously reported. In fact, prior source tracking research reports
cite accuracy ranges from 60-90 percent for various source tracking
methods; while the USGS reports accuracy rates may only be in the 20-30
percent range. The USGS-led study, Comparison of seven protocols to
identify fecal contamination sources using Escherichia coli, 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. 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. USGS said, "All too often, results of
these analyses are offered without enough validation of accuracy. 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." USGS advises, "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." Access a
release (click here). 

http://www.usgs.gov/public/press/public_affairs/press_releases/pr2016m.html





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