Determination of pharmaceuticals from various therapeutic classes in dewatered sludge by pressurized liquid extraction and high performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS)

Pharmaceuticals are released to the environment after human and animal consumption, which partly comes from accumulation in sewage sludge during wastewater treatment. This paper developed a method for the determination of N,N-diethyl-meta-toluamide (DEET) and 14 pharmaceuticals belonging to multiple therapeutic classes such as antibiotic, anti-inflammatory, antilipidemic, anti-hypertensive, and anticonvulsant in dewatered sludge. Pressurized liquid extraction using methanol/McIlvaine buffer (volume ratio, 1:1), associated with HPLC-MS/MS was proven to be effective for extraction and quantification of pharmaceuticals and DEET in dewatered sludge. Optimization procedures, including extraction method, extraction solvents and clean-up treatment, were carried out by simulating naturally aged samples to provide a more realistic extraction than previous methods, which were often done by spiking the standard solution before extraction without any aging procedures. The internal standard quantification method using six isotopically labelled compounds was applied to improve the poor absolute recoveries induced by severe matrix effects to obtain better relative recoveries (70-120%). Good relative standard deviations (lower than 19.0% for 7 repeats) and the limit of quantification (0.6-19.4 mu g/kg) indicated that the developed method was reliable and sensitive to extract and quantify the studied pharmaceuticals in dewatered sludge. For samples collected from eight sewage treatment plants in Beijing, China, it was found that trimethoprim, caffeine, ketoprofen and ibuprofen were the most prominent contaminants, with the median concentrations reaching 97.6, 179.4, 268.0 and 153.0 mu g/kg, respectively. The level of ketoprofen, ibuprofen, mefenamic acid, cabamazepine and diclofenac were similar to results reported from Spain, whilst the levels of other compounds were similar to those found in Germany, Canada and the US.