Differentiating between sources of sewage contamination
The raw sewage contamination of surface waters can be detected by using the enantioselective degradation of the chiral pharmaceutical propranolol.
Wastewater is an important source of many surface-water contaminants, including pharmaceuticals and hormones, but it has been difficult to distinguish between pollutants from untreated sewage and those from the effluents of wastewater treatment plants (WWTPs). However, a novel method presented on ES&T’s Research ASAP website (es047965T) can make this key distinction, which could enable engineers to more effectively reduce drinking-water contamination.
Untreated sewage can get into surface waters through combined sewer overflows (CSOs) during higher-than-average rainfall and snowmelt events as well as through leaking sewers. These sources of contaminants have been mostly neglected because the contributions from raw sewage are hard to discriminate from those of wastewater effluent, according to the paper’s corresponding author, David Sedlak of the civil and environmental engineering department of the University of California, Berkeley.
The method, which was developed by graduate student Lorien Fono, relies on the observation that one enantiomer of propranolol, a popular pharmaceutical, is preferentially degraded by microorganisms in WWTPs. The work that is the basis for the paper earned Fono the Graduate Student Research Paper Award from the American Chemical Society’s environmental chemistry division in August.
Storms can cause CSOs to deliver as many pharmaceuticals and endocrine disrupters to surface waters as WWTPs, Sedlak says. This is because raw sewage can contain concentrations of contaminants that are up to 1000 times higher than in wastewater effluent, he explains. Moreover, engineers want to detect the presence of raw sewage because it is often associated with waterborne pathogens, Sedlak points out.
Propranolol is a beta-blocker that is used in the treatment of high blood pressure. One of the most common prescription drugs in the U.S., propranolol exists in two mirror-image forms. Both are present in equal concentrations in the administered drug and the raw sewage. However, microorganisms in WWTPs preferentially degrade one of the mirror image forms, so the researchers could monitor changes in the isomer concentrations in the treated sewage.
Fono and Sedlak measured isomer shifts in seven WWTPs in the U.S. Using this information, Fono and Sedlak could then determine which of several surface waters they sampled were significantly impacted by raw sewage.
“I really like this new method,” says environmental chemist Thomas Poiger of Agroscope FAW in Wädenswil (Switzerland). However, he cautions that some validation work remains to be done. Poiger worries that the WWTPs investigated by Fono and Sedlak are not representative of all locations and feels that more information about the human metabolism of propranolol is necessary. “I think that a combination with other potential markers such as ibuprofen or caffeine would make the method even more powerful,” says Poiger.
“This is really innovative work,” says environmental chemist Thomas Ternes of the German Federal Institute of Hydrology in Koblenz. He says he hopes that better quantification will make it possible to calculate contaminant loads to rivers during rainfall events.
Sedlak thinks that the method has its highest potential in urban watersheds where high CSO contributions or leaky sewers are suspected. “The contaminant contribution of raw sewage has to be accounted for if pharmaceutical or hormone concentrations in drinking-water intakes are to be predicted,” Sedlak says. “Otherwise, these models will very much underestimate the actual concentrations. If you want to reduce the contaminant loads, you have to know where they are coming from,” he stresses.
