Effect of environmental conditions on polychlorinated biphenyl transformations and bacterial communities in a river sediment

Abstract

Purpose The aim of this study was to evaluate polychlorinated biphenyl (PCB) removal in relation to the associated bacterial community composition in Ohio River sediments (USA) using field and laboratory approaches. Materials and methods PCB removal was studied in different sediment layers applying dialysis equilibrators in the field for 4 months. In parallel, dissolved chemical constituents and bacterial community composition using the 16S rDNA cloning-sequencing approach were determined within the appropriate sediment layers. The effects of several bioremediation treatments on PCB removal and bacterial community composition were evaluated in laboratory experiments. Sediments spiked with 245-2'4'5' hexachlorobiphenyl were incubated under different conditions for up to 250 days, including alternating anaerobic-aerobic conditions, amendments with electron donors, FeSO 4 , and incubations at different temperatures (10°C, 25°C, 40°C). Results and discussion PCB levels remained stable in the sediment layers under field conditions. Surface sediments (0-26 cm) had elevated levels of nitrate+nitrite and sulfate, while subsurface sediments (27-35 cm) were characterized by high concentrations of ammonium, methane, and dissolved organic carbon. Oxic/anoxic conditions were also reflected in the bacterial community, with aerobic bacteria in the Bulkholderiales order enriched in the surface sediments, and anaerobic bacteria in the Clostridiales, Syntrophobacteriales, and Desulfobacterales orders more prevalent in the subsurface sediments. Although the chemical status was favorable and the potential degraders were present, PCB transformation did not take place under the prevailing environmental conditions. Under laboratory conditions, PCB transformation was positively influenced by lowered redox conditions with or without amendments with FeSO 4 , electron donors, or alternating anaerobic-aerobic conditions. The main PCB transformation process in all anaerobic treatments at 25°C was reductive dechlorination of 245-2'4'5' hexachlorobiphenyl to 24-2'4'5' pentachlorobiphenyl and 24-2'4' tetrachlorobiphenyl, which occurred at rates between 60-85% in 177 days. Exposing sediments to air for an additional period of 100 days in the sequential anaerobic-aerobic treatment did not result in additional mineralization of PCBs. Temperature, electron donors, and redox conditions significantly affected the abundance of bacteria in the Bacteroidales, Hydrogenophilales, Pseudomonales, Myxococcales, Syntrophobacterales, Acidobacterales, Caldilineales, and Clostridiales orders. The PCB dechlorinator Dehalococcoides and other dechlorinating bacteria were detected in anaerobic sediments, including Desulfitobacterium, Desulfuromonas, Anaeromyxobacter, Geobacter, and Desulfomonile. The data suggested that shifts in the bacterial communities due to abiotic conditions affected PCB transformation, either directly (degraders) or indirectly (bacterial syntrophic associations with degraders). Conclusions The data indicated that elevated redox status and low...

Divergent PCB organohalide-respiring consortia enriched from the efflux channel of a former Delor manufacturer in Eastern Europe

“…The ratio between solid material and the aqueous phase was strongly decreased. Cultivation was performed in 600 ml of liquid medium, which was 10 to 60 times the volume reported in the literature (Wu et al, 1998;Watts et al, 2005;Bedard et al, 2007;D'Angelo and Nunez, 2010;Zanaroli et al, 2010). This volume allowed for multiple samplings of total DNA and RNA and could equilibrate the possible impact of the elimination of chloride ions during the OHR process, as pH has been shown to be of critical importance (Lacroix et al, 2012).…”

“…As a consequence of 50 years of industrial activity, approximately 30 percent of the 1.3 Â 10 6 metric tons of PCB congeners was released into the environment (Meijer et al, 2003). PCBs' strong hydrophobic nature, bioaccumulation in sediment dwelling organisms, and biomagnification through the food chain (D'Angelo and Nunez, 2010), coupled with their adverse health effects, place them on the US Environmental Protection Agency's (EPA) list of potential human carcinogens.…”