Abstract:
The number of anthropogenic organic chemicals is continuously increasing and with it their substantial use in, for instance, industrial and domestic applications, agriculture and medical use. Many of these compounds are intentionally synthesized to be persistent (e.g., flame retardants, coatings) or bioactive (e.g., pesticides, pharmaceuticals), with some exhibiting the unintended characteristic of being bioaccumulative (e.g., polycyclic aromatic hydrocarbons, per- and polyfluoroalkyl substances). Thus, they pose an imminent risk to the environment with potentially far-reaching implications. Organic micropollutants are released into the aquatic environment through various input sources such as surface runoff, wastewater treatment plant effluents, combined sewer overflows, industrial sites or are, in the case of pesticides, intentionally dispersed into the environment. Inputs can be point or diffuse sources that are often not easy to identify and characterize. Rivers act as a conduit for micropollutant transport, integrating diffuse and point sources within their entire catchment and hosting important transformation processes. Therefore, the present work aimed to gain a detailed understanding of the occurrence and (toxic) effects of organic micropollutants in rivers that is required to predict their fate in the environment.
In this doctoral thesis, I investigated the chemical and toxicological profile of the Ammer River, in Southwest Germany, under varying hydrological conditions. The Ammer River is representative of small rivers in karstic systems and in densely populated temperate climate regions. I characterized input sources and the fate of organic micropollutants at the scale of the Ammer catchment via a combination of chemical analysis (liquid chromatography–mass spectrometry) and environmentally relevant in-vitro bioassays, during a series of field sampling campaigns. Organic indicator chemicals were selected based on their application, environmental relevance, occurrence in previous studies and degradability in order to indicate different input sources and in-stream processes. The bioanalytical test battery was further improved and complemented by the development of a novel in vitro bioassay (Oxygen Consumption Rate assay) that can account for two different modes of action of mitochondrial toxicity in environmental samples.
Under dry weather conditions and using chemical analysis and in-vitro bioassays, I identified a wastewater treatment plant as the major input source of organic micropollutants governing the chemical and toxicological profile of the Ammer River. Organic micropollutants were uncovered to be discharged from different input sources, with the wastewater treatment plant as the dominant input source of pharmaceuticals, industrial and household chemicals and biocides. In an 8 km long section of the Ammer, downstream of the wastewater treatment plant, compound concentrations and biological effects decreased and dilution and loss processes were uncovered. The tributaries in that river section contributed little to the overall load of compounds and mixture effects in the Ammer due to their relatively low discharge, but showed a different chemical and toxicological profile.
During a storm event, the chemical and toxicological profile of the Ammer significantly changed. The numbers, concentrations and fluxes of organic micropollutants and associated effects were generally higher and suspended particulate matter turned out to be an important transport vector for effects and for hydrophobic target compounds. Organic micropollutants discharged from agricultural and urban areas, combined sewer overflow and the wastewater treatment plant. Thus, changing hydrological conditions may trigger the occurrence and the increase of organic micropollutant concentrations, mass fluxes, associated effects and the importance of particle-facilitated transport in rivers, which can pose a risk to the aquatic environment and are, at present, not considered in risk assessment and management options. Although both approaches, chemical analysis and in-vitro bioassays, are complementary as they cover different compounds and compound classes, they showed a similar pollution profile of the Ammer.
In this thesis I showed that the chemical and toxicological profile of a river is highly variable in time and space, specifically driven by varying hydrological conditions that act to partition input sources of organic micropollutants, and thus their individual mass-flux contribution. It is therefore important for the investigation of the fate of organic micropollutants in rivers, of factors driving in-stream processes (e.g., degradation, sorption) and for future regulatory monitoring efforts to consider and properly capture these spatiotemporal variations.
Organic Micropollutants