Effect-based analyses as tools to assess the impact of differently treated effluents on fish and aquatic ecosystem health

Abstract

Many surface waters are suffering from anthropogenic pressures, including pollutant emissions. Anthropogenic substances enter the aquatic environment through various pathways with wastewater treatment plants belonging to the most important sources. The technologies that are presently used in conventional wastewater treatment often fail to remove all substances. Consequently, numerous compounds are continuously discharged via effluents into surface waters, where they can be detected on a regular basis. Many studies revealed that traces of chemicals, so-called micropollutants, may pose a considerable threat to aquatic organisms. These findings led to the development of different strategies to reduce trace substances in surface waters, ranging from source control to so-called “end-of-pipe” strategies. One important measure is the expansion of conventional wastewater treatment plants by additional purification steps. Here, removing substances via adsorption to powdered activated carbon is a promising approach for large-scale application. Yet, little is known about the efficiency of this purification process with respect to ecosystem health. In my doctoral thesis, I used effect-based analyses to characterize the effect of differently treated wastewater effluents on fish health. For this purpose, I combined in situ exposure of rainbow trout at two conventionally equipped wastewater treatment plants with subsequent biomarker analyses. In addition, the present thesis includes studies conducted in the context of the research project SchussenAktivplus, which aimed to examine the effect of expanding a wastewater treatment plant by an additional powdered activated carbon stage on the ecosystem of the receiving river Schussen. For this, a comprehensive approach combining different chemical and biological analyses prior and subsequent to the implementation of the additional purification stage was adopted. My studies showed that fish health can be considerably impaired by discharges of conventionally equipped wastewater treatment plants. An additional adsorption stage significantly reduced micropollutant loads in the effluent and thus mitigated the adverse effects in exposed fish. Moreover, this positive effect was also reflected on other levels of biological organisation, thus showing the benefit of wastewater treatment plant upgrading. However, during my studies, adverse effects could sometimes also be detected in fish exposed at the reference site located upstream of the respective wastewater treatment plant. Thus, the degree of adverse reactions in exposed fish was not only linked to the type of wastewater treatment. The general water quality of the receiving river, which also depends on pollution inputs upstream of the wastewater treatment plants under investigation, and the composition of the raw wastewater also seemed to play an important role. Hence, the local conditions should be taken into account when decisions on the necessity and the type of wastewater treatment plant upgrading have to be made.