Validation of an integrative methodology to assess and monitor reductive dechlorination of chlorinated ethenes in contaminated aquifers

Bioremediation of tetra-and trichloroethene-contaminated aquifers is requently hampered due to incomplete dechlorination to the more toxic dichloroethene (DCE) and vinyl chloride (VC), indicating insufficient knowledge about the biological mechanisms related to aquifer functioning. A methodology based on the joint analysis of geochemical and microbiological datasets was developed to assess the presence of the biochemical potential for complete reductive dechlorination to harmless ethene and to explain the reasons for which degradation often stalls at the more toxic intermediates. This methodology is composed of three successive steps, with i) the acquisition of geochemical data including chlorinated ethenes, ii) the detailed analysis of the bacterial community structures as well as the biochemical potential for complete dechlorination using microcosms and molecular detection of organohalide-respiring bacteria and key reductive dehalogenases, and iii) a statistical Multiple Factor Analysis combining the above mentioned abiotic and biotic variables in a functional modelling of the contaminated aquifer. The methodology was validated by analyzing two chlorinated ethenes-contaminated sites. Results from the first site showed that the full biochemical potential for ethene production was present in situ. However, redox potential was overall too high and locally manganese reduction out-competed chlorinated ethenes reduction, explaining the reasons for the local accumulation of DCE and VC to a lesser extent. The second contaminated aquifer was under bioremediation by successive cheese whey injections. Analysis demonstrated that cheese whey additions led to increasingly reduced redox conditions and that hampered reductive dechlorination was not due to competition with other anaerobic respiration processes. Complete reductive dechlorination to ethene was preferentially occurring under methanogenic conditions. DCE and VC accumulation was probably induced first by low pH resulting from whey fermentation and at a later stage by phosphate limitation. In conclusions, the proposed methodology successfully allowed the identification of biogeochemical processes limiting or supporting complete dechlorination in both aquifers. The integrative approach provided fundamental information about the functional heterogeneity of the contaminated aquifers in time and space, and can be used as a reliable tool to support corrective decision-making in the development of remediation strategies based on natural attenuation of chlorinated ethenes.

An ecological approach for understanding the reductive dechlorination process of chlorinated ethenes in contaminated aquifers

Christof Holliger, Pierre Rossi, Sonia Estelle Tarnawski

Chlorinated ethenes, frequently encountered contaminants in groundwater, are often found to be incompletely dechlorinated to dichloroethene and vinyl chloride, more toxic products that accumulate in the aquifer. Some of the concerns in designing remediation approaches based on biological dechlorination are i) the presence of bacteria capable of completely reducing chlorinated ethenes, and ii) the competition events for available electron donors between classical biogeochemical processes and the reductive dechlorination process. For this purpose, an assessment methodology was developed to explore the existing relations between autochthonous bacterial communities, degradation state of chlorinated ethenes and redox processes, including reductive dechlorination. Three steps are involved with first the acquisition of abiotic environmental data, followed by assessing the biochemical potential for complete dechlorination and an analysis of bacterial community structures, and finally a statistical Multiple Factor Analysis combining datasets from geochemistry and microbiology. This approach was applied for diagnosing a Swiss aquifer for its in situ potential of complete reductive dechlorination, and for monitoring a Czech aquifer under bioremediation by successive cheese whey injections. The Swiss site contained the microbiological potential for complete dechlorination but the global redox conditions were not enough reducing and dichloroethene reduction was in competition locally with manganese reduction. The follow-up of the Czech site has shown that during the remediation process, complete reductive dechlorination was favored under sulfate-reducing conditions, but was in competition with other anaerobic bacterial processes leading to a transient accumulation of dichloroethene and vinyl chloride. In both cases, antagonist biogeochemical processes were identified as the reasons restricting the reductive dechlorination at the level of toxic intermediates. This approach is now formalized in a user-oriented manual, and could be integrated as tool for eligibility investigation of aquifers for a bioremediation strategy through natural attenuation.

2015

Biogeography and spatial variability of bacterial communities associated with chloroethene – contaminated aquifers

François Gillet, Christof Holliger, Pierre Rossi, Noam Shani

Numerous industries and facilities have been using chlorinated ethenes (CEs) as non-flammable solvents since the beginning of the 20th century. These compounds are known to persist in the environment, exerting adverse effects. They have been considered for a long time as totally resistant to any form of microbial degradation. Advances in this field since the 1980’s showed that several bacteria can couple the reductive dechlorination of CEs to energy conservation in a process called dehalorespiration. Objectives The formation and composition of the microbial habitat, as well as the structure of the bacterial communities (in terms of cell density and species composition), are thought to be related directly to the dehalorespiration activity and to have an influence on the dehalorespiring guild diversity. Methods The bacterial communities present in 104 water samples coming from nine Quaternary European aquifers were analyzed using a standardized T-RFLP analysis. These aquifers showed various sizes and depths and were all contaminated by substantial amounts of PCE. Chemical and contaminant compositions were recorded as well. Results Strong relationships have been observed between the structure of the communities and both geological and environmental data sets, showing an apparent perfect adequacy between the bacterial cells and their specific habitat. In general, each aquifer hosted a specific bacterial community, whose variation was lower than the variation measured among all aquifers. No clear geographical pattern could be found among all aquifers, although temperature was an important variable that contributed apparently to the structuring of the communities. Surprisingly, statistical analysis showed that CEs did not play an important role in the structuring of the communities, even though a partial or total reductive dehalogenation process could be observed in all aquifers. T-RFs corresponding putatively to already known guild members could be detected in almost all water samples, but they contributed marginally (10 ± 7.4 %, in 85 water samples) to the community profiles. Furthermore, these T-RFs showed a remarkably low fidelity index and were consequentlnever linked specifically to any of the observed aquifers

2009

BIOGEOGRAPHY AND SPATIAL VARIABILITY OF BACTERIAL COMMUNITIES ASSOCIATED WITH CHLOROETHENE – CONTAMINATED AQUIFERS

François Gillet, Christof Holliger, Pierre Rossi, Noam Shani

Numerous industries and facilities have been using chlorinated ethenes (CEs) as non-flammable solvents since the beginning of the 20th century. These compounds are known to persist in the environment, exerting adverse effects. They have been considered for a long time as totally resistant to any form of microbial degradation. Advances in this field since the 1980’s showed that several bacteria can couple the reductive dechlorination of CEs to energy conservation in a process called dehalorespiration. The formation and composition of the microbial habitat, as well as the structure of the bacterial communities (in terms of cell density and species composition), are thought to be related directly to the dehalorespiration activity and to have an influence on the dehalorespiring guild diversity. The bacterial communities present in 104 water samples, from nine CE-contaminated Quaternary European aquifers, were analyzed using a standardized T-RFLP analysis. Strong relationships have been observed between the structure of the communities and both geological and environmental data sets, showing an apparent perfect adequacy between the bacterial cells and their specific habitat. In general, each aquifer hosted a specific bacterial community, whose variation was lower than the variation measured among all aquifers. No clear geographical pattern could be found among all aquifers, although temperature was an important variable that contributed apparently to the structuring of the communities. Surprisingly, statistical analysis showed that CEs did not play an important role in the structuring of the communities, even though a partial or complete reductive dehalogenation process could be observed in all aquifers. T-RFs corresponding putatively to already known guild members could be detected in almost all water samples, but they contributed marginally to the community profiles. Furthermore, these T-RFs showed a remarkably low fidelity index and were consequently never linked specifically to any of the observed aquifers.

2009

BIOGEOGRAPHY AND SPATIAL VARIABILITY OF BACTERIAL COMMUNITIES ASSOCIATED WITH CHLOROETHENE – CONTAMINATED AQUIFERS

François Gillet, Christof Holliger, Pierre Rossi, Noam Shani

Numerous industries and facilities have been using chlorinated ethenes (CEs) as non-flammable solvents since the beginning of the 20th century. These compounds are known to persist in the environment, exerting adverse effects. They have been considered for a long time as totally resistant to any form of microbial degradation. Advances in this field since the 1980’s showed that several bacteria can couple the reductive dechlorination of CEs to energy conservation in a process called dehalorespiration. The formation and composition of the microbial habitat, as well as the structure of the bacterial communities (in terms of cell density and species composition), are thought to be related directly to the dehalorespiration activity and to have an influence on the dehalorespiring guild diversity. The bacterial communities present in 104 water samples, from nine CE-contaminated Quaternary European aquifers, were analyzed using a standardized T-RFLP analysis. Strong relationships have been observed between the structure of the communities and both geological and environmental data sets, showing an apparent perfect adequacy between the bacterial cells and their specific habitat. In general, each aquifer hosted a specific bacterial community, whose variation was lower than the variation measured among all aquifers. No clear geographical pattern could be found among all aquifers, although temperature was an important variable that contributed apparently to the structuring of the communities. Surprisingly, statistical analysis showed that CEs did not play an important role in the structuring of the communities, even though a partial or complete reductive dehalogenation process could be observed in all aquifers. T-RFs corresponding putatively to already known guild members could be detected in almost all water samples, but they contributed marginally to the community profiles. Furthermore, these T-RFs showed a remarkably low fidelity index and were consequently never linked specifically to any of the observed aquifers.

2009

An ecological approach for understanding the reductive dechlorination process of chlorinated ethenes in contaminated aquifers

Christof Holliger, Pierre Rossi, Sonia Estelle Tarnawski

2015

Biogeography and spatial variability of bacterial communities associated with chloroethene – contaminated aquifers

François Gillet, Christof Holliger, Pierre Rossi, Noam Shani

2009