This thesis investigates the effects of pharmaceutical substances on coastal Baltic Sea organisms. Despite an increasing awareness of the occurrence of pharmaceuticals in various aquatic compartments, current knowledge of their possible effects on non-target organisms is limited. Especially scarce is the knowledge concerning possible long-term effects, mixture-effects, effects on non-standard test organisms and indirect effects from interactions among organisms. Also the environmental fate, availability and distribution of pharmaceuticals between sediment, water and biota is only rarely investigated.

The aim of this thesis was therefore to investigate the biological effects of pharmaceuticals, and their distribution in organisms of a coastal Baltic Sea community. In four studies, blue mussels, amphipods and macroalgae were exposed to pharmaceuticals in laboratory experiments. The effects from exposure, as well as recovery from the same, were studied on different physiological variables. With increasing complexity of experiment designs, the tested substances were found to affect aquatic organisms from different hierarchical levels both through direct negative effects, as well as through indirect positive effects within model communities. Moreover, the studies showed that the organisms were affected by exposure to environmentally relevant concentrations, but also that exposed organisms could recover from the exposure. Effects from pharmaceutical mixtures occurred in lower concentrations than effects from single pharmaceutical substances, and high internal concentrations of two pharmaceuticals – diclofenac and propranolol – were detected in exposed organisms.

The detected effects and the uptake of pharmaceuticals in biota demonstrate a possible problem for aquatic environments, but especially for the Baltic Sea, since this is a naturally sensitive ecosystem with low species diversity, low functional redundancy and a history of heavy pollution.