Degradation of 1,2-dichloroethane by microbial communities from river sediment at various redox conditions

Insight into the pathways of biodegradation and external factors controlling their activity is essential in adequate environmental risk assessment of chlorinated aliphatic hydrocarbon pollution. This study focuses on biodegradation of 1,2-dichloroethane (1,2-DCA) in microcosms containing sediment sourced from the European rivers Ebro, Elbe and Danube. Biodegradation was studied under different redox conditions. Reductive dechlorination of 1,2-DCA was observed with Ebro and Danube sediment with chloroethane, or ethene, respectively, as the major dechlorination products. Different reductively dehalogenating micro-organisms (Dehalococcoides spp., Dehalobacter spp., Desulfitobacterium spp. and Sulfurospirillum spp.) were detected by 16S ribosomal RNA gene-targeted PCR and sequence analyses of 16S rRNA gene clone libraries showed that only 2-5 bacterial orders were represented in the microcosms. With Ebro and Danube sediment, indications for anaerobic oxidation of 1,2-DCA were obtained under denitrifying or iron-reducing conditions. No biodegradation of 1,2-DCA was observed in microcosms with Ebro sediment under the different tested redox conditions. This research shows that 1,2-DCA biodegradation capacity was present in different river sediments, but not in the water phase of the river systems and that biodegradation potential with associated microbial communities in river sediments varies with the geochemical properties of the sediments.