December 2, 2011
TRACES of common pain-killing drugs are being transformed into toxic forms by waste water treatment plants, a new report from researchers at the University of NSW shows.
The study, which used samples from water treatment plants across Sydney and some interstate plants, showed that the organic sludge used to help destroy household chemicals can actually transform them into something else.
The altered chemicals from three widely-used household drugs were detected at very low levels, meaning that there is minimal risk to human health. But the consequences could be much larger for some aquatic environments where treated water is reused.
”There are hundreds and thousands of different drugs out there, and so it is a pretty fair assumption that some of the things emerging from treatment are a lot more toxic than we thought,” said one of the study’s authors, Stuart Khan, from the water research centre at the University of NSW.
Some drugs occur in two forms, called ”enantiomers”, which are very similar but not quite identical. ”Chemically, they are like a mirror image of each other; different in the same way a right hand and a left hand are different from each other,” Dr Khan said.
Sometimes pairs of enantiomers have different effects on living organisms, and when this happens, the enantiomer with a beneficial effect is separated from its toxic mirror image, and turned into a safe drug.
The key to the new findings is that careful testing of water samples from treatment plants were compared with fresh water and water containing raw sewage, including samples from the heavily-polluted Cooks River. The sewage contained the enantiomers associated with ordinary pharmaceuticals that are flushed down toilets or sinks across the city. But the treated waste water samples showed that the organic ”scrubbing” by bacteria in treatment plants had restored some of the toxic enantiomers.
The most infamous case of a chemical being transformed into a toxic chemical took place in the 1950s, when the drug thalidomide was administered to pregnant women but was changed to a toxic form in the human gut, causing birth defects.
”What this research means is that we really need to think about this question of measuring toxins a lot more broadly,” Dr Khan said.
The study was published in the peer-reviewed journal Water Research, and follow-up work is now being done on the effects of waste water treatment on other chemicals.