Abteilung Umweltchemie

Herbicide pollution in headwater streams due to agricultural practices is a major environmental concern and is characterized by episodic peak concentrations from fast transport paths. We rely on previous experimental studies in a small (1.2km²) agricultural catchment in the Swiss Plateau, to model dynamic diffuse herbicide pollution with emphasis on fast transport paths in a conceptual modelling framework at the catchment scale. We show how experimentalists’ understanding of the fate of herbicides (perceptual model) can be translated into conceptual models considering sorption, degradation, and fast transport of water and chemicals facilitated by impervious surfaces, tile drains and artificial shortcuts. Different types of experimental data (streamflow, high-frequency concentration measurements, and soil–water distribution coefficients) are used in a joint Bayesian inference of model parameters. We assess the ability of different spatial configurations of hydrological response units in explaining observed heterogeneity in transport behaviour of two corn herbicides. Thereby, we find that (1) relatively simple conceptual models can provide a realistic description of herbicide fate in small agricultural catchments, (2) accounting for spray drift onto hard surfaces is necessary to avoid a severe model bias during the first rainfall event after application, and (3) including catchment-specific experimentalist knowledge about important elements like artificial shortcuts and tile drains leads to a reduction in uncertainty of 30% compared to the more conventional conception of the proximity to the stream as the dominant risk factor.

Enzymatic oxygenations initiate biodegradation processes of many organic soil and water contaminants. Even though many biochemical aspects of oxygenation reactions are well-known, quantifying rates of oxidative contaminant removal as well as the extent of oxygenation remains a major challenge. Because enzymes use different strategies to activate O₂, reactions leading to substrate oxygenation are not necessarily limiting the rate of contaminant removal. Moreover, oxygenases react along unproductive pathways without substrate metabolism leading to O₂ uncoupling. Here, we identify the critical features of the catalytic cycles of selected oxygenases that determine rates and extents of biodegradation. We focus most specifically on Rieske dioxygenases, a subfamily of mononuclear non-heme ferrous iron oxygenases, because of their ability to hydroxylate unactivated aromatic structures and thus initiate the transformation of the most persistent organic contaminants. We illustrate that the rate-determining steps in their catalytic cycles range from O₂ activation to substrate hydroxylation, depending on the extent of O-O cleavage that is required for generating the reactive Fe-oxygen species. The extent of O₂ uncoupling, on the other hand, is highly substrate-specific and potentially modulated by adaptive responses to oxidative stress. Understanding the kinetic mechanisms of oxygenases will be key to assess organic contaminant biotransformation quantitatively.

This study presents a nontarget approach to detect discharges from pharmaceutical production in municipal wastewater treatment plant (WWTP) effluents and to estimate their relevance on the total emissions. Daily composite samples were collected for 3 months at two WWTPs in Switzerland, measured using liquid chromatography high-resolution mass spectrometry, and time series were generated for all features detected. The extent of intensity variation in the time series was used to differentiate relatively constant domestic inputs from highly fluctuating industrial emissions. We show that an intensity variation threshold of 10 correctly classifies compounds of known origin and reveals clear differences between the two WWTPs. At the WWTP receiving wastewater from a pharmaceutical manufacturing site, (i) 10 times as many potential industrial emissions were detected as compared to the WWTP receiving purely domestic wastewater; (ii) for 11 pharmaceuticals peak concentrations, >10 μg/L and up to 214 μg/L were quantified, which are clearly above typical municipal wastewater concentrations; and (iii) a pharmaceutical not authorized in Switzerland was identified. Signatures of potential industrial emissions were even traceable at the downstream Rhine monitoring station at a >4000-fold dilution. Several of them occurred repeatedly, suggesting that they were linked to regular production, not to accidents. Our results demonstrate that small wastewater volumes from a single industry not only left a clear signature in the effluents of the respective WWTP but also influenced the water quality of one of Europe's most important river systems. Overall, these findings indicate that pharmaceutical production is a relevant emission source even in highly developed countries with a strong focus on water quality, such as Switzerland.

Biotransformation plays a crucial role in regulating the bioaccumulation potential and toxicity of organic compounds in organisms but is, in general, poorly understood for emerging contaminants. Here we have used diclofenac as a model compound to study the impact of biotransformation on the bioaccumulation potential and toxicity in two keystone aquatic invertebrates: Gammarus pulex and Hyalella azteca. In both species, diclofenac was transformed into several oxidation products and conjugates, including two novel products, i.e. diclofenac taurine conjugate (DCF-M403) and unexpected diclofenac methyl ester (DCF-M310.03). The ratios of biotransformation products to parent compound were 12-17 for DCF-M403 and 0.01-0.7 for DCF-M310.03 after 24 h exposure. Bioconcentration factors (BCFs) of diclofenac were 0.5 and 3.2 L kg ww^-1 in H. azteca and G. pulex, respectively, whereas BCFs of DCF-M310.03 was 164.5 L kg ww^-1 and 104.7 L kg ww^-1, respectively, representing a 25 to 110-fold increase. Acute toxicity of DCF-M310.03 was also higher than the parent compound in both species, which correlated well with the increased bioconcentration potential. The LC50 of diclofenac in H. azteca was 216 mg L^-1, while that of metabolite DCF-M310.03 was reduced to only 0.53 mg L^-1, representing a 430-fold increase in acute toxicity compared to diclofenac. DCF-M403 is less toxic than its parent compound towards H. azteca, which may be linked to its slightly lower hydrophobicity. Furthermore, the transformation of diclofenac to its methyl ester derivative was explored in crude invertebrate extracts spiked with an S-adenosylmethionine cofactor, revealing possible catalysis by an S-adenosylmethionine-dependent -carboxylic acid methyltransferase. Methylation of diclofenac was further detected in fish hepatocytes and human urine, indicating a broader relevance. Therefore, potentially methylated metabolites of polar contaminants should be considered for a comprehensive risk assessment in the future.