Reactive transport of micropollutants in laboratory aquifers undergoing transient exposure periods

• Published in: The Science of the total environment Vol. 856; no. part 2; p. 159170
• Main Authors: Prieto-Espinoza, Maria, Di Chiara Roupert, Raphaël, Belfort, Benjamin, Weill, Sylvain, Imfeld, Gwenaël
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2023; Elsevier
• Subjects: Bacterial diversity; Biodegradation; CSIA; Environmental Sciences; Micropollutants; Modeling; Stream-groundwater interactions; Biodegradation; Micropollutants; Stream-groundwater interactions; Bacterial diversity; Modeling; CSIA
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.159170

Groundwater quality is of increasing concern due to the ubiquitous occurrence of micropollutant mixtures. Stream-groundwater interactions near agricultural and urban areas represent an important entry pathway of micropollutants into shallow aquifers. Here, we evaluated the biotransformation of a micropollutant mixture (i.e., caffeine, metformin, atrazine, terbutryn, S-metolachlor and metalaxyl) during lateral stream water flow to adjacent groundwater. We used an integrative approach combining concentrations and transformation products (TPs) of the micropollutants, compound-specific isotope analysis (δ13C and δ15N), sequencing of 16S rRNA gene amplicons and reactive transport modeling. Duplicate laboratory aquifers (160 cm × 80 cm × 7 cm) were fed with stream water and subjected over 140 d to three successive periods of micropollutant exposures as pulse-like (6000 μg L−1) and constant (600 μg L−1) injections under steady-state conditions. Atrazine, terbutryn, S-metolachlor and metalaxyl persisted in both aquifers during all periods (<10 % attenuation). Metformin attenuation (up to 14 %) was only observed from 90 d onwards, suggesting enhanced degradation over time. In contrast, caffeine dissipated during all injection periods (>90 %), agreeing with fast degradation rates (t1/2 < 3 d) in parallel microcosm experiments and detection of TPs (theobromine and xanthine). Significant stable carbon isotope fractionation (Δδ13C ≥ 6.6 ‰) was observed for caffeine in both aquifers, whereas no enrichment in 15N occurred. A concentration dependence of caffeine biotransformation in the aquifers was further suggested by model simulations following Michaelis-Menten kinetics. Changes in bacterial community composition reflected long-term bacterial adaptation to micropollutant exposures. Altogether, the use of an integrative approach can help to understand the interplay of subsurface hydrochemistry, bacterial adaptations and micropollutants biotransformation during stream-groundwater interactions. [Display omitted] •Biotransformation of micropollutants in lateral stream-groundwater transition zones.•CSIA data and TPs evidenced caffeine degradation during transient exposure periods.•Model simulations highlight concentration dependency for caffeine biotransformation.•Adaptation of bacterial communities after acute and chronic exposure over 140 days.•Integrative approach for assessing micropollutant biotransformation during stream-groundwater interactions.