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

Biocides, pharmaceuticals and personal care products in widespread use are released into surface waters as complex mixtures. Even at low environmental concentrations, the persistence and toxic effects of these micropollutants to aquatic ecosystems are a source of growing concern. At the sediment-water interface (SWI), the partitioning of micropollutants influences their abiotic and biotic dissipation and impact the exposure and responses of prokaryotic communities. Using microcosm experiments mimicking the SWI, we examined the dissipation of metformin (antidiabetic drug), metolachlor (agricultural herbicide) and terbutryn (urban herbicide in building material), either alone or as a model mixture, and corresponding changes in prokaryotic communities. Complete dissipation of MFN and MET was observed, while TER persisted (DT50TER: 53 to 231 days). Dissipation parameters of individual micropollutants did not differ significantly when present in mixture. In contrast, 16S rRNA-based analysis suggested a matrix-dependent response of prokaryotic communities. Accounting for all taxa, the mixture exhibits additive effect in water compartment, with MET and TER identified as the main contributors, although synergistic, antagonistic, additive and mean interaction effects were observed in water and the sediment. In the evaluation of risks associated with multiple contamination in aquatic ecosystems, it is crucial to consider the characteristics of the micropollutants, their potential interactions and the involved matrices.