Abstract
Metoprolol is widely used as a beta-blocker and considered an emerging contaminant of environmental concern due to pseudo persistence in wastewater effluents that poses a potential ecotoxicological threat to aquatic ecosystems. Microbial removal of metoprolol in the redox-delineated hyporheic zone (HZ) was investigated using streambed sediments supplemented with 15 or 150 μM metoprolol in a laboratory microcosm incubation under oxic and anoxic conditions. Metoprolol disappeared from the aqueous phase under oxic and anoxic conditions within 65 and 72 days, respectively. Metoprolol was refed twice after initial depletion resulting in accelerated disappearance under both conditions. Metoprolol disappearance was marginal in sterile control microcosms with autoclaved sediment. Metoprolol was transformed mainly to metoprolol acid in oxic microcosms, while metoprolol acid and α-hydroxymetoprolol were formed in anoxic microcosms. Transformation products were transient and disappeared within 30 days under both conditions. Effects of metoprolol on the HZ bacterial community were evaluated using DNA- and RNA-based time-resolved amplicon Illumina MiSeq sequencing targeting the 16S rRNA gene and 16S rRNA, respectively, and were prominent on 16S rRNA rather than 16S rRNA gene level suggesting moderate metoprolol-induced activity-level changes. A positive impact of metoprolol on Sphingomonadaceae and Enterobacteriaceae under oxic and anoxic conditions, respectively, was observed. Nitrifiers were impaired by metoprolol under oxic and anoxic conditions. Collectively, our findings revealed high metoprolol biodegradation potentials in the hyporheic zone under contrasting redox conditions associated with changes in the active microbial communities, thus contributing to the attenuation of micropollutants.Key points• High biotic oxic and anoxic metoprolol degradation potentials in the hyporheic zone.• Key metoprolol-associated taxa included Sphingomonadaceae, Enterobacteraceae, and Promicromonosporaceae.• Negative impact of metoprolol on nitrifiers.
Highlights
The occurrence of residual organic micropollutants such as pharmaceuticals in receiving rivers is of great concern sinceAppl Microbiol Biotechnol (2021) 105:6103–6115 organisms, and a risk to humans when the surface water is used for the production of drinking water.Microbial removal of metoprolol in the hyporheic zone of receiving rivers has recently been reported (Posselt et al 2018; Schaper et al 2018)
The detected initial metoprolol concentration completely disappeared from the aqueous phase in the 15 and 150 μM metoprolol treatments incubated under oxic conditions within 65 and 72 days, respectively, after an initial lag phase of approximately 40 days (Fig. 1a)
Our findings are consistent with previous studies conducted in situ on the same river that reported both biodegradation and sorption as the critical attenuation mechanisms for metoprolol in the hyporheic zone (Posselt et al 2018; Schaper et al 2019)
Summary
Microbial removal of metoprolol in the hyporheic zone of receiving rivers has recently been reported (Posselt et al 2018; Schaper et al 2018). With the hyporheic zone naturally characterized by an oxic benthic and underlying anoxic sediments (Galloway et al 2019; Schaper et al 2019), it is expected that the microbial metoprolol degraders and associated biodegradation potentials in these redox-delineated sediment zones vary. The present study investigated the effect of redox conditions on metoprolol removal and associated microbial community structure in hyporheic zone sediments. Our objectives were to (i) determine metoprolol biodegradation potentials in hyporheic zone sediments under oxic and anoxic conditions, (ii) assess the response of the indigenous bacterial communities in metoprolol-impacted oxic and anoxic hyporheic zone sediments, and (iii) identify metoprolol tolerant as well as sensitive microbes
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