Combined effects of micropollutants and their degradation on prokaryotic communities at the sediment-water interface.

Pesticides and pharmaceuticals enter aquatic ecosystems as complex mixtures. Various processes govern their dissipation and effect on the sediment and surface waters. These micropollutants often show persistence and can adversely affect microorganisms even at low concentrations. We investigated the dissipation and effects on procaryotic communities of metformin (antidiabetic drug), metolachlor (agricultural herbicide), and terbutryn (herbicide in building materials). These contaminants were introduced individually or as a mixture (17.6 µM per micropollutant) into laboratory microcosms mimicking the sediment-water interface. Metformin and metolachlor completely dissipated within 70 days, whereas terbutryn persisted. Dissipation did not differ whether the micropollutants were introduced individually or as part of a mixture. Sequence analysis of 16S rRNA gene amplicons evidenced distinct responses of prokaryotic communities in both sediment and water. Prokaryotic community variations were mainly driven by matrix composition and incubation time. Micropollutant exposure played a secondary but influential role, with pronounced effects of recalcitrant metolachlor and terbutryn within the micropollutant mixture. Antagonistic and synergistic non-additive effects were identified for specific taxa across taxonomic levels in response to the micropollutant mixture. This study underscores the importance of considering the diversity of interactions between micropollutants, prokaryotic communities, and their respective environments when examining sediment-water interfaces affected by multiple contaminants.