Diurnal drug variations at wastewater plant

The diurnal variations of legal and illicit drugs in wastewater at a treatment plant have been measured relative to creatinine, which allows more detailed analysis of usage trends. The presence of illegal drugs like cocaine in wastewater and river water has been used to estimate drug use in the related catchment areas on land, but these measurements do not allow a detailed examination of the variations throughout a particular day.

Now, scientists from the USA, Switzerland and Australia have devised a method for measuring the hourly levels of drugs as they enter a wastewater treatment plant. Samples were collected every 6 minutes and and combined to give 1-hour composites which were analysed by LC-tandem-MS for creatinine, caffeine, methamphetamine, cocaine, and the cocaine metabolite benzoylecgonine.

Creatinine is already used in clinical studies as a reference point because it is always excreted in urine. In this case, as the authors describe in Environmental Science and Technology, the diurnal variations in creatinine concentrations in wastewater are confirmed then used to reveal the normalised hourly loads of each drug. The variations within one day were related to human activities such as commuting into the catchment area, morning wake-up times and recreational time.