The Effects of Antimicrobials on Aquatic Ecosystems

Antimicrobials are widely detected in freshwater systems, where organisms are exposed to complex mixtures rather than single compounds. This thesis examined how such contamination affects aquatic ecosystems by linking environmental occurrence, ecological responses, internal exposure, trophic transfer, and the ecological consequences of advanced wastewater treatment. Combining field investigations, controlled experiments, chemical analysis, microbial profiling, and quantitative modelling, the research showed that antimicrobial effects are strongly context-dependent across environmental compartments, background conditions, and trophic levels. Mixture effects were often non-additive, and functional endpoints revealed ecological changes not captured by community structure alone. Limited transfer to higher trophic levels did not necessarily imply low ecological risk, because dietary exposure could still impair predator performance. Although advanced wastewater treatment reduced chemical pressure, it could also reshape microbial communities and functions. Overall, this thesis highlights the need to integrate external exposure, internal exposure, mixture pressure, and functional ecological responses in freshwater risk assessment and management.