Understanding the Removal and Fate of Selected Drugs of Abuse in Sludge and Biosolids from Australian Wastewater Treatment Operations

Illicit and pharmaceutical drugs are considered to be emerging contaminants of concern, and much research effort has gone into assessing their occurrence in wastewater. However, little information exists on their presence in treated sludge or biosolids. In this study, we examined sludge and biosolids from a large metropolitan wastewater treatment plant (WWTP) in Australia to determine the occurrence of five drugs of abuse, including benzoylecgonine as indicator of cocaine consumption, methamphetamine and 3,4-methylenedioxy methamphetamine (MDMA) as representative illicit stimulants, and codeine and morphine as pharmaceuticals with potential environmental risk. The samples were solid-phase extracted and analyzed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Benzoylecgonine and MDMA were present in raw sludge but were notably degraded during solids treatment processes, and were not detected in the dewatered sludge (after treatment) or in biosolids. Methamphetamine, codeine, and morphine were detected in all biosolids samples at mean concentrations of 20–50 μg·kg⁻¹. The presence of these three drugs in biosolids shows that these compounds are relatively stable in the solids and in soil, and can persist in biosolids for at least several years. A simple environmental risk assessment based on estimated risk quotients (RQs) for these compounds indicated that the potential environmental risks associated with the land application of biosolids are very low at typical Australian biosolids application rates.