Communication Dans Un Congrès Année : 2025

Bacterial degradation of the toxic halogenated solvent dichloromethane in aquifer microcosms: impact of disturbances in physico-chemical parameters

Carmen Lázaro Sánchez
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  • IdRef : 283568356
Stéphane Vuilleumier
Emilie Muller

Résumé

The ability of a microbial population to degrade a pollutant in situ also depends on the physicochemical parameters it is exposed to. Dichloromethane (DCM, CH2Cl2) is a toxic industrial solvent, frequently detected in groundwater and biodegradable under both oxic and anoxic conditions. Previous work with laboratory-scale aquifers demonstrated that DCM biodegradation was more pronounced under fluctuating water level conditions. We hypothesized that matrix porosity, which strongly impacts water content and redox conditions in aquifers, affects DCM bioremediation in natural environments. To test this, we studied the effect of matrix granulometry, water content and oxygen concentration, and the response of a drastic change in oxygen concentration on DCM biodegradation kinetics and bacterial community composition.

Laboratory microcosms with beads of 2, 0.5 or 0.1 mm of diameter were set up with contaminated industrial groundwater showing DCM biodegradation. Experiments involved addition of 7 successive pulses of 1 mM DCM at different water content, i.e. water saturation, water holding capacity (WHC) or ½ WHC, and under different oxygen conditions, i.e. stable oxic or anoxic conditions, or disturbed with a sudden switch in oxygen content.

The obtained results showed that water content act as a first selection barrier, since the community did not degrade DCM when water content was very low. In addition, the onset of the activity was faster at higher water contents. When water content was not a limiting factor, oxygen concentration was the main driving force behind both the activity and composition of the microbial community, with anoxic conditions being the main limiting factor for DCM biodegradation and taxonomic richness. Furthermore, an effect of water content on community composition was observed under oxic conditions, suggesting that, under anoxic conditions, the community had a more deterministic dynamic. The matrix granulometry also influenced the DCM-degrading community activity and composition, but mainly through its control over water content. In particular, finer grain sizes facilitated the maintenance of the activity of the DCM degrading microbial community at the lowest tested water content (i.e., ½ WHC). Finally, the effect of a disturbance in oxygen content differed depending on the initial conditions, and ranged from susceptibility to disturbance to the emergence of the DCM degradation function.

Taken together, our results suggest that granulometry informs the effect of water content on DCM biodegradation and bacterial community composition. In contrast, the effect of oxygen content on DCM biodegradation was independent of grain size.

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Dates et versions

hal-05216815 , version 1 (22-08-2025)

Identifiants

  • HAL Id : hal-05216815 , version 1

Citer

Carmen Lázaro Sánchez, Gwenael Imfeld, Stéphane Vuilleumier, Emilie Muller. Bacterial degradation of the toxic halogenated solvent dichloromethane in aquifer microcosms: impact of disturbances in physico-chemical parameters. FEMS Micro, Jul 2025, Milan (Italie), France. ⟨hal-05216815⟩
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