When antibiotics in wastewater are not broken down by treatment they get into the environment, where bacteria are gradually becoming resistant to them, say the researchers.
At a conference of the American Chemical Society held in Denver, Colorado, earlier this year, Olya Keen, a professor of civil and environmental engineering at the University of North Carolina at Charlotte, described how she and a colleague investigated doxycycline - a widely used antibiotic that commonly ends up in wastewater effluents and the environment.
The researchers found that disinfection with chlorine transforms doxycycline in wastewater into new antibiotic compounds, as Prof. Keen explains:
"Wastewater treatment is designed to break down biological substances, but not antibiotics. Surprisingly enough, though, we are finding in the lab that not only is chlorine not breaking down antibiotics, but it is actually creating even stronger antibiotics than the original doxycycline."
Typical wastewater treatments involve disinfection using ultraviolet radiation, ozone and chlorine. These help to reduce concentrations of pharmaceutical compounds in wastewater.
There are several ways that antibiotics and other drugs can end up in wastewater. When we take antibiotics, they are not all broken down in the body and get passed into wastewater. Drugs that have passed their expiry date also get dumped into the sewage system from homes and hospitals. Another route is the discharge of antibiotic materials from pharmaceutical companies.
"Wastewater tests have found every type of antibiotic known," Prof. Keen says. "The problem antibiotics cause when they are not broken down by treatment is they get into streams, where bacteria are becoming immune to them, and more dangerous, superbug, bacteria can be formed."
Traditionally, the effectiveness of wastewater treatment has been assessed according to the disappearance of the parent contaminants. More recently, however, scientists have been looking at other ways such as looking at what new compounds are formed.
Prof. Keen and her co-investigator Nicole Kennedy-Neth, a doctoral student, argue that not enough attention has been given to the new compounds that can arise from the effect of chlorination on pharmaceutical contaminants - despite chlorination being the main means by which both drinking water and wastewater are disinfected.
Evidence calls for a re-evaluation of wastewater disinfection methods
For their study, they investigated the effect of chlorine on doxycycline and measured changes in antibacterial activity of the new compounds that result from the reaction.
They found that some of the "transformation products" have antibiotic properties and several of these could be helping antibiotic-resistant microbes to arise in the environment, even when the parent doxycycline molecule is no longer present.
On the basis of their evidence, the researchers call for a re-evaluation of wastewater disinfection methods, as Prof. Keen explains:
"This research is a small piece of a larger question. There are varieties of antibiotics found in wastewater, and at this point we are just testing one. It is in a class of antibiotics that all have similar compositions, so we anticipate that other antibiotics in this class may respond the same way."
For this initial study, the researchers prepared controlled samples in the laboratory, where they treated doxycycline with chlorine. Then, using a mass spectrometer, they identified compounds in the various samples. They now plan to do the same with real wastewater samples.
They hope to eventually find better ways of breaking down antibiotics during wastewater treatment or keeping them out of wastewater in the first place.
In the following video, Prof. Keen discusses the research with delegates at the meeting.
Meanwhile, MNT reported earlier this year how man-made pollution may be affecting fish living up to a mile deep in the northeast Atlantic Ocean by changing their sex organs and livers.