Combined effects of micropollutants on prokaryotic communities at the sediment-water interface

Pesticides and pharmaceuticals enter aquatic ecosystems as complex mixtures. Various processes govern their dissipation and impact on the sediment and surface waters. These micropollutants often show persistence and adverse effects on 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) added individually or as a mixture (17.6 µM per micropollutant) to laboratory microcosms mimicking the sediment-water interface. Complete dissipation of metformin and metolachlor occurred within 70 days, while terbutryn persisted. Dissipation did not differ when micropollutants were present individually or as part of a mixture. Sequence analysis of 16S rRNA gene amplicons evidenced distinct responses of prokaryotic communities in sediment and water. Micropollutant exposure was the second factor contributing to the observed variations in prokaryotic communities, with a pronounced effect of recalcitrant metolachlor and terbutryn on the overall effect of the micropollutant mixture. Non-additive antagonistic and synergistic effects of micropollutants were detected for specific taxa across taxonomic levels. Our study highlights the importance of considering the diversity of potential interactions between micropollutants, prokaryotic communities, and their respective environments in investigations of multi-contaminated sediment-water interfaces.