To estimate drug consumption more reliably, wastewater-based epidemiology would benefit from a better understanding of drug residue stability during in-sewer transport. We conducted batch experiments with real, fresh wastewater and sewer biofilms. Experimental conditions mimic small to medium-sized gravity sewers with a relevant ratio of biofilm surface area to wastewater volume (33 m2 m–3). The influences of biological, chemical, and physical processes on the transformation of 30 illicit drug and pharmaceutical residues were quantified. Rates varied among locations and over time. Three substances were not stable—that is, >20% transformation, mainly due to biological processes—at least for one type of tested biofilm for a residence time ≤2 h: amphetamine, 6-acetylcodeine, and 6-monoacetylmorphine. Cocaine, ecgonine methyl ester, norcocaine, cocaethylene, and mephedrone were mainly transformed by chemical hydrolysis and, hence, also unstable in sewers. In contrast, ketamine, norketamine, O-desmethyltramadol, diclofenac, carbamazepine, and methoxetamine were not substantially affected by in-sewer processes under all tested conditions and residence times up to 12 h. Our transformation rates include careful quantification of uncertainty and can be used to identify situations in which specific compounds are not stable. This will improve accuracy and uncertainty estimates of drug consumption when applied to the back-calculation.@en

Little is known about the significance of hospitals as point sources for emission of organic micropollutants into the aquatic environment. A mass flow analysis of pharmaceuticals and diagnostics used in hospitals was performed on the site of a representative Swiss cantonal hospital. Specifically, we analyzed the consumption of iodinated X-ray contrast media (ICM) and cytostatics in their corresponding medical applications of radiology and oncology, respectively, and their discharge into hospital wastewater and eventually into the wastewater of the municipal wastewater treatment plant. Emission levels within one day and over several days were found to correlate with the pharmacokinetic excretion pattern and the consumed amounts in the hospital during these days. ICM total emissions vary substantially from day to day from 255 to 1259 g/d, with a maximum on the day when the highest radiology treatment occurred. Parent cytostatic compounds reach maximal emissions of 8-10 mg/d. A total of 1.1%, 1.4%, and 3.7% of the excreted amounts of the cytostatics 5-fluorouracil, gemcitabine, and 2′,2′-difluorodeoxyuridine (main metabolite of gemcitabine), respectively, were found in the hospital wastewater, whereas 49% of the total ICM was detected, showing a high variability among the compounds. These recoveries can essentially be explained by the high amount administered to out-patients (70% for cytostatics and 50% for ICM); therefore, only part of this dose is expected to be excreted on-site. In addition, this study emphasizes critical issues to consider when sampling in hospital sewer systems. Flow proportional sampling over a longer period is crucial to compute robust hospital mass flows.@en

A model to predict the mass flows and concentrations of pharmaceuticals predominantly used in hospitals across a large number of sewage treatment plant (STP) effluents and river waters was developed at high spatial resolution. It comprised 427 geo-referenced hospitals and 742 STPs serving 98% of the general population in Switzerland. In the modeled base scenario, domestic, pharmaceutical use was geographically distributed according to the population size served by the respective STPs. Distinct hospital scenarios were set up to evaluate how the predicted results were modified when pharmaceutical use in hospitals was allocated differently; for example, in proportion to number of beds or number of treatments in hospitals. The hospital scenarios predicted the mass flows and concentrations up to 3.9 times greater than in the domestic scenario for iodinated X-ray contrast media (ICM) used in computed tomography (CT), and up to 6.7 times greater for gadolinium, a contrast medium used in magnetic resonance imaging (MRI). Field measurements showed that ICM and gadolinium were predicted best by the scenarios using number of beds or treatments in hospitals with the specific facilities (i.e., CT and/or MRI). Pharmaceuticals used both in hospitals and by the general population (e.g., cyclophosphamide, sulfamethoxazole, carbamazepine, diclofenac) were predicted best by the scenario using the number of beds in all hospitals, but the deviation from the domestic scenario values was only small. Our study demonstrated that the bed number-based hospital scenarios were effective in predicting the geographical distribution of a diverse range of pharmaceuticals in STP effluents and rivers, while the domestic scenario was similarly effective on the scale of large river-catchments.@en