Exemplary wastewater treatment mixed with pristine surface waters made the Duluth, Minn., area an ideal location for this study. Credit: University of Minnesota |
A
new University of Minnesota study reveals that the release of treated
municipal wastewater—even wastewater treated by the highest-quality
treatment technology—can have a significant effect on the quantities of
antibiotic-resistant bacteria, often referred to as “superbacteria,” in
surface waters.
The
study also suggests that wastewater treated using standard technologies
probably contains far greater quantities of antibiotic-resistant genes,
but this likely goes unnoticed because background levels of bacteria
are normally much higher than the water studied in this research.
The
new study is led by civil engineering associate professor Timothy
LaPara in the University of Minnesota, Twin Cities College of Science
and Engineering. The study is published in the most recent issue of “Environmental Science and Technology,”
a journal of the American Chemical Society. The research was part of a
unique class project in a graduate-level civil engineering class at the
University of Minnesota focused on environmental microbiology.
Antibiotics
are used to treat numerous bacterial infections, but the
ever-increasing presence of antibiotic-resistant bacteria has raised
substantial concern about the future effectiveness of antibiotics. In
response, there has been increasing focus on environmental reservoirs of
antibiotic resistance over the past several years. Antibiotic use in
agriculture has been heavily scrutinized, while the role of treated
municipal wastewater has received little attention as a reservoir of
resistance.
Antibiotic-resistant
bacteria develop in the gastrointestinal tracts of people taking
antibiotics. These bacteria are then shed during defecation, which is
collected by the existing sewer infrastructure and passed through a
municipal wastewater treatment facility.
In
this study, the Ph.D. students and professor examined the impact of
municipal wastewater in Duluth, Minn., on pristine surface waters by
gathering water samples from the St. Louis River, Duluth-Superior
Harbor, and Lake Superior in northeastern Minnesota. The treatment
facility in Duluth is considered one of the best. After solids and
biological matter are removed, the Duluth wastewater treatment is one of
only a few in the country that filter water a third time through a
mixed media filter to remove additional particles of bacteria and
nutrients. Standard wastewater treatment treats water twice to remove
solids and biological matter.
“This
was a unique and ideal location for this study because of the exemplary
wastewater treatment mixed with surprisingly pristine surface waters
with very low background levels of bacteria that wouldn’t mask our
results,” LaPara said. “Previous studies in which treated municipal
wastewater was implicated as a source of antibiotic resistance were more
convoluted because multiple sources of antibiotic resistance genes
existed, such as agricultural activity and industrial wastewater
discharges.”
While
the levels of overall bacteria were still relatively low in the surface
water samples, researchers in the University of Minnesota study found
that the quantities of antibiotic-resistant genes and human-specific
bacteria were typically 20-fold higher at the site where treated
wastewater was released into the Duluth-Superior Harbor compared to
nearby surface water samples.
“Current
wastewater treatment removes a very large fraction of the antibiotic
resistance genes,” LaPara said. “But this study shows that wastewater
treatment operations need to be carefully considered and more fully
studied as an important factor in the global ecology of antibiotic
resistance.”
In
addition to LaPara, researchers involved in the study include civil
engineering Ph.D. students Tucker Burch, Patrick McNamara, David Tan;
and bioproducts and biosystems engineering Ph.D. student Mi Yan, with
help from soil, water and climate Ph.D. student Jessica Eichmiller.
The
University of Minnesota research study was funded by the National
Science Foundation’s broader impacts effort, which combines research and
education. The Minnesota Environment and Natural Resources Trust Fund
paid for time on the R/V Blue Heron ship to collect water samples.
