A CSU study is the first in its kind to demonstrate that
antibiotics fed to livestock are ending up in waterways, according
to an Oct. 19 press release.
Ken Carlson, an associate professor of civil engineering, has
been investigating the presence of antibiotics in Colorado
waterways for two years and has found that antibiotics used only in
animal feed are present in public waterways.
Previous studies demonstrated that antibiotics were present in
public waterways, but there was no way to trace their origins so
Carlson decided to track monensin, an antibiotic used exclusively
in animal feed. When the study revealed the presence of monensin in
public waterways, it showed that livestock antibiotics were somehow
entering the watershed.
“Monesin is only used for feed, for enhancing growth,” he said.
“There aren’t any human uses and it’s not even used
Now Carlson and his co-investigators are trying to track the
antibiotic’s path from livestock grounds to public waterways. Like
many pharmaceuticals, most of the active ingredients in monensin
are not absorbed by animals, so residual antibiotics end up in
manure and in wastewater storage lagoons.
“I think it’s at least 75 percent (of the antibiotics) is
excreted without being changed,” said Jessica Davis, a professor of
soil and crop sciences and co-investigator on the project.
Wastewater treatment plants remove some of the antibiotic
residue, Davis said, but there are still antibiotics that are not
Major concerns related to the drug’s presence in the public
waterway include the potential negative effect on aquatic life and
the possibility that releasing such antibiotics into the
environment will increase antibiotic resistance among dangerous
bacteria, Carlson said.
Antibiotic resistance has been a growing concern in recent
decades, with many scientists and medical groups worrying that a
tendency to overuse antibiotics has allowed many dangerous bacteria
to develop partial or total immunity to the drugs, according the
U.S. Food and Drug Administration’s Web site, www.fda.gov.
While the investigators publish the results of their findings,
research will continue, Carlson said. He and his colleagues are
investigating how antibiotics travel from agricultural areas into
the watershed, as well as searching for ways to degrade the
“We don’t just want to raise the red flag and say, ‘Look,
they’re here,’ and go home,” Carlson said.
He noted that the levels of antibiotics are extremely low, but
warned that they could still affect the environment.
“The ag industry would like it to go away,” Carlson said. “We’re
not willing to do that but we’re also not willing to say the sky is
falling. (The public’s) drinking water’s not at risk.”
Carlson’s colleagues agreed, saying that further research is
“The thing with pharmaceuticals is they’re active at very low
levels,” said co-investigator Amy Pruden, an assistant professor of
civil engineering, citing DDT, a pesticide used in the ’60s and
’70s that was found to disrupt birds’ reproductive cycle.
Pruden is studying animal waste in an effort to reduce
antibiotic presence. Carlson noted that leaving wastewater exposed
to sunlight might help break down antibiotics.
“We feel that the growing and feed operations contributes to
(the antibiotics’ presence),” Carlson said. “We want to know, is
that one of the primary routes for the compounds getting from the
farms to the rivers?”
The researchers hope that determining how the antibiotics get
into waterways will provide insight into stopping the process.
“Maybe there’s just some simple thing you can change,” Pruden
said. Davis and Carlson agreed, noting that they are focused on
working with farmers and ranchers to eliminate the antibiotics in
Carlson, Pruden and Davis all agreed that while the research is
noteworthy, the public should not be alarmed.
“It’s just a preliminary, ‘hey, these antibiotics are there,'”