Department Environmental Chemistry

Pharmaceuticals and their human metabolites are significant sources of micropollutants in the aquatic environments due to incomplete removal during wastewater treatment. While parent compounds have been widely studied, the fate of their metabolites across treatment stages remains poorly understood, despite the fact that most pharmaceuticals are excreted in metabolized forms. Using a combination of full-scale wastewater treatment plant (WWTP) observations, laboratory experiments, and modeling, this study aimed to assess and compare the removal of 290 parent pharmaceuticals and 154 human metabolites across biological and advanced wastewater treatment stages, to evaluate the influence of human metabolic modifications on removal rates. The findings from the field data confirmed that phase II metabolites are often efficiently degraded during biological treatment, and cleaved into corresponding parent compounds or phase I metabolites, with median removals of 84% to 97% in the three WWTPs. In contrast, phase I metabolites show a similar behavior to their parent compounds and are often not more efficiently abated, with median removals ranging between 38% to 53% for parents and phase I metabolites. Advanced treatments, including ozonation with and without granular activated carbon filtration, showed significant median reductions of 79% to 92% for parent pharmaceuticals and 54% to 82% for metabolites, with removal efficiencies correlating with ozone doses. Laboratory biotransformation experiments identified reaction-specific pseudo-first-order rate constants, with carboxylic acids showing increased persistence, potentially as a result of their high oxidation state, which limits further degradation under aerobic conditions. Moreover, the laboratory experiments confirmed that acetylated and glucuronidated phase II metabolites are more efficiently abated during biological treatment, while sulfates are more stable compared to their parent compounds. A mechanistic model using the experimentally determined biotransformation rate constants was established, showing strong agreement with measured data for compounds with high or low biotransformation rates. Predictions for partially degraded compounds showed higher uncertainty, reflecting the complex interactions between biotransformation, sorption and operational parameters. This work provides a detailed assessment of the behavior and fate of pharmaceuticals and especially their metabolites during wastewater treatment, emphasizes the importance of understanding transformation pathways, and offers valuable insights for optimizing removal strategies and minimizing environmental impacts.

Wastewater as a medium contains information on both circulating pathogens and drug consumption at the population level. This study combines tracking of respiratory viruses and quantification of pharmaceuticals as untargeted indicators of symptoms related to acute respiratory infections and influenza-like illnesses such as coughing, fever and pain. From January 2021 to June 2024, raw wastewater samples from ten locations covering 23% of the Swiss population were analysed. This encompassed 15 pharmaceuticals and four priority respiratory viruses including severe acute respiratory syndrome coronavirus virus-2 (SARS-CoV-2), respiratory syncytial virus (RSV), influenza A and influenza B viruses. The pharmaceutical compounds dextromethorphan, pheniramine, clarithromycin, acetaminophen and codeine showed a strong correlation with respiratory virus loads in wastewater. This enabled the estimation of pathogen-specific and cumulative symptom treatment in the population. In 2021 and 2024, notable increases in pharmaceutical loads without corresponding increases in viral loads signalled high community symptoms linked to unsurveilled pathogens. This study demonstrates that pharmaceutical surveillance can inform respiratory disease burden and highlights the value of integrated surveillance for assessing emerging public health threats beyond those routinely monitored.

Antibiotics are of environmental concern. Their concentrations in the aquatic environment are frequently studied, while their occurrence in human excreta-derived fertilizers is less investigated. Therefore, levels of antibiotics, preservatives with antimicrobial properties, and various other micropollutants were determined in sewage sludge and in human fecal compost. Digested sludge of 29 Swiss wastewater treatment plants was analyzed, representing about 2.6 Mio people (30% of the Swiss population). This was compared with residues found in compost with dry toilet content after thermophilic composting, representing about 10 000 people. Fluoroquinolones and preservatives dominate in Swiss sewage sludge with weighted mean concentrations of 6500 μg kg⁻¹ and 2300 μg kg⁻¹. Levels of macrolides (240 μg kg⁻¹), β-lactam transformation products (35 μg kg⁻¹) and sulfonamides (15 μg kg⁻¹) were lower. Pollution patterns in digested sewage sludge were relatively constant throughout Switzerland. Levels of contamination in fecal compost were approximately 30 times lower than in sewage sludge. Pollution patterns differed between compost and sludge. Chemicals used in down-the-drain-applications (e.g., preservatives from personal care products or corrosion inhibitors) are less relevant in compost. Based on the Swiss consumption and excretion data, a mass flow analysis was carried out for antibiotics and pharmaceuticals in sludge and compost. The mass flow analysis in sludge showed a good agreement of predicted and measured concentrations for compounds that tend to sorb to organic matter (e.g., fluoroquinolones). Currently, there is no specific legislation that regulates the use of fecal compost from dry toilets as fertilizer. However, the one to two order of magnitude lower levels of contaminants in fecal compost compared to sludge and manure indicate a lower environmental risk when applying it as fertilizer.

Oxygen isotope ratios of O₂ are important tracers for assessing biological activity in biogeochemical processes in aquatic environments. In fact, changes in the ¹⁸O/¹⁶O and ¹⁷O/¹⁶O ratios of O₂ have been successfully implemented as measures for quantifying photosynthetic O₂ production and biological O₂ respiration. Despite evidence for light-dependent O₂ consumption in sunlit surface waters, however, photochemical O₂ loss processes have so far been neglected in the stable isotope-based evaluation of oxygen cycling. Here, we established the magnitude of the O isotope fractionation for abiotic photochemical O₂ elimination through formation of singlet O_2, ¹O₂, and the ensuing oxygenation and oxidation reactions with organic compounds through experiments with rose bengal as the ¹O₂ sensitizer and three different amino acids and furfuryl alcohol as chemical quenchers. Based on the kinetic analysis of light-dependent O₂ removal in the presence of different quenchers, we rationalize the observable O isotope fractionation of O₂ and the corresponding, apparent ¹⁸O kinetic isotope effects (¹⁸O-AKIE) with a pre-equilibrium model for the reversible formation of ¹O₂ and its irreversible oxygenation reactions with organic compounds. While ¹⁸O-AKIEs of oxygenation reactions amount to 1.03, the O isotope fractionation of O₂ decreased to unity with increasing ratio of the rates of oxygenation reaction of ¹O₂ vs ¹O₂ decay to ground state oxygen, ³O₂. Our findings imply that O isotope fractionation through photochemical O₂ consumption with isotope enrichment factors, ¹⁸O-ϵ, of up to −30‰ can match contributions from biological respiration at typical dissolved organic matter concentrations of lakes, rivers, and oceans and should, therefore, be included in future evaluations of biogeochemical O₂ cycling.