Chloroethene Biodegradation Research Articles

Correlations between maximum reductive dechlorination rates and specific biomass parameters in Dehalococcoides mccartyi consortia enriched on chloroethenes PCE, TCE and cis-1,2-DCE.

One of the challenges to implementing the modeling of the biological reductive dechlorination (RD) process is the evaluation of biological parameters that represent the abundance/activity levels of the microorganisms involved in the biodegradation of chloroethenes. Here we report a combined analysis of kinetic and specific biomass parameters conducted on three dechlorinating consortia enriched on PCE, TCE and cis-1,2-DCE. In these consortia, Dehalococcoides mccartyi (Dhc) represented ≥70% of the bacterial population identified via 16S rRNA gene amplicon sequencing. Quantitative biomolecular methods were used to generate specific biomass parameters targeting either the Dhc population (16S rRNA genes or cells) or specific genes encoding RD process-involved reductive dehalogenases. The correlation factor between the abundance of active Dhc cells or tceA gene copies and maximum RD rates allowed to predict an increment of 7E+09 of active Dhc cells or 5E+09 tceA gene copies/L under controlled conditions. Diversely, the utilization of gene transcripts as biomass parameters for RD modeling did not provide reliable correlations with kinetic performances. This study provides valuable insights for further modeling of the RD process through the utilization of specific biomass parameters.

Combined use of ISCR and biostimulation techniques in incomplete processes of reductive dehalogenation of chlorinated solvents

Pools of chloroethenes are more recalcitrant in the transition zone between aquifers and basal aquitards than those elsewhere in the aquifer. Although biodegradation of chloroethenes occur in this zone, it is a slow process and a remediation strategy is needed. The aim of this study was to demonstrate that combined strategy of biostimulation and in situ chemical reduction (ISCR) is more efficient than the two separated strategies. Four different microcosm experiments with sediment and groundwater of a selected field site where an aged perchloroethene (PCE)-pool exists at the bottom of a transition zone, were designed under i) natural conditions, ii) biostimulation with lactic acid, iii) in situ chemical reduction (ISCR) with zero valent iron (ZVI) and under iv) a combined strategy with lactic acid and ZVI. Biotic and abiotic dehalogenation, terminal electron acceptor processes and evolution of microbial communities were investigated for each experiment. The main results where: i) limited reductive dehalogenation of PCE occurs under sulfate-reducing conditions; ii) biostimulation with lactic acid promotes a more pronounced reductive dehalogenation of PCE in comparison under natural conditions, but resulted in an accumulation of cis-dichloroethene (cDCE); iii) ISCR with zero-valent iron (ZVI) facilitates a sustained dehalogenation of PCE and its metabolites to non-halogenated products, however, the iv) combined strategy results in the fastest and sustained dehalogenation of PCE to non-halogenated products in comparison of all four set-ups. These findings suggest that biostimulation and ISCR with ZVI are the most suitable strategy for a complete reductive dehalogenation of PCE-pools in the transition zone.

Migration of chlorinated hydrocarbons in multilayer unconsolidated porous media: a case study from the Po Plain, Italy

Chlorinated solvents are the most ubiquitous organic contaminants found in groundwater since the last six decades. Due to their high degree of carcinogenicity/toxicity and the relatively high mobility and persistence, they represent a serious threat against the human health and the environment. These contaminants generally reach groundwater as Dense Non-Aqueous Phase Liquid (DNAPL) that can migrate through aquifers easier than aqueous contaminants. The complex phase partitioning to which chlorinated solvent DNAPLs can undergo (i.e. to the dissolved, vapor or sorbed phase), as well as their transformations (e.g. degradation), depend on the physico-chemical properties of the contaminants and on the features of the hydrogeological system in which they migrate. The hydrogeologic setting below the city of Ferrara (Po plain, northern Italy), which is affected by scattered contamination by chlorinated solvents, has been investigated. In particular, a limited-inspace high-resolution investigation was performed in one selected contaminated test-site, known as “Caretti site”. Here, high-resolution vertical profiling of different kind of data (i.e. stratigraphic data, hydraulic heads, hydrochemical composition of water, stable isotopes of water and contaminants) were collected by means of multilevel monitoring systems and other innovative sampling and analytical techniques. The main goals of the research were to assess the intrinsic vulnerability of the aquifers and to identify the dynamics of migration and transformation of the chloroethene contaminants in relationship to the features of the hosting porous medium. The confined aquifers turned out to be more vulnerable to DNAPLs than aqueous contaminants due to the occurrence of microfractures in the overlying clayey aquitards. The presence of organic-rich deposits in the local stratigraphy enhanced the biodegradation of chloroethenes causing accumulation of Vinyl Chloride. The results are useful at the local scale, e.g. to interpret the origin of contamination in other sites of the Ferrara area, and also at the global scale, to better address future remediation and protection actions in similar settings.

Reductive dechlorination in recalcitrant sources of chloroethenes in the transition zone between aquifers and aquitards.

In the transition zone between aquifers and basal aquitards, the perchloroethene pools at an early time in their evolution are more recalcitrant than those elsewhere in the aquifer. The aim of this study is to demonstrate that the biodegradation of chloroethenes from aged pools (i.e., pools after decades of continuous groundwater flushing and dissolution) of perchloroethene is favored in the transition zone. A field site was selected where an aged pool exists at the bottom of a transition zone. Two boreholes were drilled to obtain sediment and groundwater samples to perform chemical, isotopic, molecular, and clone library analyses and microcosm experiments. The main results were as follows: (i) the transition zone is characterized by a high microbial richness; (ii) reductively dechlorinating microorganisms are present and partial reductive dechlorination coexists with denitrification, Fe and Mn reduction, and sulfate reduction; (iii) reductively dechlorinating microorganisms were also present in the zone of the aged pool; (v) the high concentrations of perchloroethene in this zone resulted in a decrease in microbial richness; (vi) however, the presence of fermenting microorganisms supplying electrons for the reductively dechlorinating microorganisms prevented the reductive dechlorination to be inhibited. These findings suggest that biostimulation and/or bioaugmentation could be applied to promote complete reductive dechlorination and to enhance the dissolution of more nonaqueous phase liquids (DNAPL).

Reinterpreting the Importance of Oxygen‐Based Biodegradation in Chloroethene‐Contaminated Groundwater

Chlororespiration is common in shallow aquifer systems under conditions nominally identified as anoxic. Consequently, chlororespiration is a key component of remediation at many chloroethene‐contaminated sites. In some instances, limited accumulation of reductive dechlorination daughter products is interpreted as evidence that natural attenuation is not adequate for site remediation. This conclusion is justified when evidence for parent compound (tetrachloroethene, PCE, or trichloroethene, TCE) degradation is lacking. For many chloroethene‐contaminated shallow aquifer systems, however, nonconservative losses of the parent compounds are clear but the mass balance between parent compound attenuation and accumulation of reductive dechlorination daughter products is incomplete. Incomplete mass balance indicates a failure to account for important contaminant attenuation mechanisms and is consistent with contaminant degradation to nondiagnostic mineralization products like CO2. While anoxic mineralization of chloroethene compounds has been proposed previously, recent results suggest that oxygen‐based mineralization of chloroethenes also can be significant at dissolved oxygen concentrations below the currently accepted field standard for nominally anoxic conditions. Thus, reassessment of the role and potential importance of low concentrations of oxygen in chloroethene biodegradation are needed, because mischaracterization of operant biodegradation processes can lead to expensive and ineffective remedial actions. A modified interpretive framework is provided for assessing the potential for chloroethene biodegradation under different redox conditions and the probable role of oxygen in chloroethene biodegradation.

Characterization of Groundwater Microbial Communities, Dechlorinating Bacteria, and In Situ Biodegradation of Chloroethenes Along a Vertical Gradient

The variability of hydrogeochemical conditions can affect groundwater microbial communities and the natural attenuation of organic chemicals in contaminated aquifers. It is suspected that in situ biodegradation in anoxic plumes of chloroethenes depends on the spatial location of the contaminants and the electron donors and acceptors, as well as the patchiness of bacterial populations capable of reductive dechlorination. However, knowledge about the spatial variability of bacterial communities and in situ biodegradation of chloroethenes in aquifers is limited. Here, we show that changes of the bacterial communities, the distribution of putative dechlorinating bacteria and in situ biodegradation at the border of a chloroethenes plume (Bitterfeld, Germany) are related to local hydrogeochemical conditions. Biotic reductive dechlorination occurred along a 50 m vertical gradient, although significant changes of the hydrogeochemistry and contaminant concentrations, bacterial communities and distribution of putative dechlorinating bacteria (Dehalobacter spp., Desulfitobacterium spp., Dehalococcoides spp., and Geobacter spp.) were observed. The occurrence and variability of in situ biodegradation of chloroethenes were revealed by shifts in the isotope compositions of the chloroethenes along the vertical gradient (δ13C ranging from −14.4‰ to −4.4‰). Our results indicate that habitat characteristics were compartmentalized along the vertical gradient and in situ biodegradation occurred with specific reaction conditions at discrete depth. The polyphasic approach that combined geochemical and biomolecular methods with compound-specific analysis enabled to characterize the spatial variability of hydrochemistry, bacterial communities and in situ biodegradation of chloroethenes in a heterogeneous aquifer.

Influence of Mass-Transfer Limitations on Carbon Isotope Fractionation during Microbial Dechlorination of Trichloroethene

Mass transfer of organic contaminants from nonaqueous phase liquids to the aqueous phase can significantly modulate the observable carbon isotope fractionation behavior associated with contaminant transformation. We evaluated the effects of kinetic interphase mass transfer between tetradecane and water on the observable (13)C enrichment factor, epsilon(obs), pertinent to the reductive dechlorination of trichloroethene (TCE) by Sulfurospirillum sp. in laboratory batch model systems containing organic, aqueous and gaseous phases. We propose a conceptual model, which includes the kinetics of tetradecane-water and gas-water mass transfer, microbial growth, and isotope-sensitive parameters describing dehalorespiration, for quantifying variable (13)C enrichment factors. While the C isotope fractionation of TCE reduction to cis-dichloroethene (cDCE) in the absence of phase-transfer effects can be characterized by a constant epsilon-value of -18.8 +/- 0.6 per thousand, mass-transfer limitations impede describing this process with a constant enrichment factor typically used in Rayleigh equations. Owing to the masking of kinetic isotope effects by the transfer of TCE from tetradecane to the aqueous phase, (obs)-values gradually changed from -18.4 per thousand to -5.9 per thousand. Such variations may complicate the interpretation of compound-specific isotope analysis in the assessment of chloroethene biodegradation in field applications.

Flowpath Independent Monitoring of Reductive Dechlorination Potential in a Fractured Rock Aquifer

AbstractThe flowpath dependent approaches that are typically employed to assess biodegradation of chloroethene contaminants in unconsolidated aquifers are problematic in fractured rock settings, due to difficulties defining discrete groundwater flowpaths in such systems. In this study, the variation in the potential for chloroethene biodegradation with depth was evaluated in a fractured rock aquifer using two flowpath independent lines of field evidence: (1) the presence of the three biochemical prerequisites [electron donor(s), chloroethene electron acceptor(s), and chlororespiring microorganism(s)] for efficient chloroethene chlororespiration and (2) the in situ accumulation of chloroethene reductive dechlorination daughter products. The validity of this approach was assessed by comparing field results with the results of [1, 2‐14C] cis‐DCE microcosm experiments. Microcosms were prepared with depth‐specific core material, which was crushed and emplaced in discrete packer intervals for 1 year to allow colonization by the indigenous microbial community. Packer intervals characterized by significant electron donor concentrations, elevated numbers of chlororespiring microorganisms, and high reductive dechlorination product to parent contaminant ratios correlated well with the production of 14C‐labeled reductive dechlorination products in the microcosm experiments. These results indicate that, in the absence of information on discrete groundwater flowpaths, a modified approach emphasizing flowpath independent lines of evidence can provide insight into the temporal and spatial variability of contaminant biodegradation in fractured rock systems.

Stimulation of aerobic degradation of chlorinated ethenes in soil by microbial inoculation

AbstractDegradation of chlorinated ethenes under aerobic conditions has been reported using a cometabolic pathway. A site in Illinois had shallow contamination and sandy soils, which in combination created aerobic conditions. The aerobic conditions prevented the degradation of chlorinated ethenes by reductive dechlorination. Biodegradation of chloroethenes under aerobic conditions does not occur naturally at all sites; however, it can be enhanced if microorganisms capable of cometabolic degradation are introduced into the soil. In this study, trichloroethene (TCE) removal in the soil was enhanced by the injection of a commercially available microbial inoculum (CL‐OUT® inoculum, CL‐Solutions, Cincinnati, OH) and nutrients and was compared to chlorinated ethene removal in soil that had received nutrients only and soil that had received activated sludge and nutrients. Trichloroethene removal was measured after one week, seven weeks, and eleven weeks.After one week, no significant TCE removal had occurred in any of the test microcosms. After seven weeks, a slight decrease in TCE levels accompanied by an increase in cis‐1,2‐dichloroethene (cis‐1,2‐DCE) was seen in the microcosms that had received CL‐OUT®. After 11 weeks, a marked decrease in TCE levels was observed in the microcosms that had received CL‐OUT®. No significant TCE decrease was observed in any of the other microcosms. These data suggest that organisms capable of aerobic TCE degradation were not present at the site; however, the addition of an inoculum containing such organisms enabled aerobic degradation to occur. © 2008 Wiley Periodicals, Inc.

Accumulation of dechlorination daughter products: A valid metric of chloroethene biodegradation

AbstractIn situ reductive dechlorination of perchloroethene (PCE) and trichloroethene (TCE) generates characteristic chlorinated (cis‐dichloroethene [cis‐DCE] and vinyl chloride [VC]) and nonchlorinated (ethene and ethane) products. The accumulation of these daughter products is commonly used as a metric for ongoing biodegradation at field sites. However, this interpretation assumes that reductive dechlorination is the only chloroethene degradation process of any significance in situ and that the characteristic daughter products of chloroethene reductive dechlorination persist in the environment. Laboratory microcosms, prepared with aquifer and surface‐water sediments from hydrologically diverse sites throughout the United States and amended with [1,2‐14C] TCE, [1,2‐14C] DCE, [1,2‐14C] DCA, or [1,2‐14C] VC, demonstrated widely variable patterns of intermediate and final product accumulation. In predominantly methanogenic sediment treatments, accumulation of 14C‐DCE, 14C‐VC, 14C‐ethene, and 14C‐ethane predominated. Treatments characterized by significant Fe(III) and/or Mn(IV) reduction, on the other hand, demonstrated substantial, and in some cases exclusive, accumulation of 14CO2 and 14CH4. These results suggest that relying on the accumulation of cis‐DCE, VC, ethene, and ethane may substantially underestimate overall chloroethene biodegradation at many sites. © 2007 Wiley Periodicals, Inc.*This article is a U.S. government work and, as such, is in the public domain in the United States of America.

Une approche innovante pour modéliser la biodégradation des composés organochlorés volatils en aquifères poreux

The goal of this study was to develop an innovative chloroethene biodegradation module based on biological, thermodynamical and mechanistic concepts. The biodegradation scheme was based on the postulate that in each part of an aquifer only one degradation mechanism is dominant: the one involving the most energetic electron acceptor. Thus, the selection of the active degradation mechanism was a function of the concentration of different electron acceptors. Modified Monod-type kinetics was used in order to take into account the possible influence of some compounds on the biodegradation of a given organic compound. The numerical model developed was applied to a simple test case, whose results are presented here. To cite this article: F. Nex et al., C. R. Geoscience 338 (2006).

Guest Editorial: Contaminant Source Zones: Remediation or Perpetual Stewardship?

Guest Editorial: Contaminant Source Zones: Remediation or Perpetual Stewardship?

Comment on “Methane As a Product of Chloroethene Biodegradation under Methanogenic Conditions”

ADVERTISEMENT RETURN TO ISSUEPREVCorrespondence/Rebut...Correspondence/RebuttalNEXTComment on “Methane As a Product of Chloroethene Biodegradation under Methanogenic Conditions”Jan DolfingView Author Information AB-DLO Wageningen, The NetherlandsCite this: Environ. Sci. Technol. 1999, 33, 13, 2302–2303Publication Date (Web):May 26, 1999Publication History Published online26 May 1999Published inissue 1 July 1999https://doi.org/10.1021/es9902625Copyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views191Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (37 KB) Get e-AlertsSUBJECTS:Anions,Degradation,Free energy,Hydrocarbons,Vinyl Get e-Alerts

Response to Comment on “Methane As a Product of Chloroethene Biodegradation under Methanogenic Conditions”

Response to Comment on “Methane As a Product of Chloroethene Biodegradation under Methanogenic Conditions”

Methane As a Product of Chloroethene Biodegradation under Methanogenic Conditions

Radiometric detection headspace analyses of microcosms containing bed sediments from two geographically distinct sites indicated that 10−39% of the radiolabeled carbon transformed during anaerobic biodegradation of [1,2-14C]trichloroethene (TCE) or [1,2-14C]vinyl chloride (VC) under methanogenic conditions was ultimately incorporated into 14CH4. The results demonstrate that, in addition to ethene, ethane, and CO2, CH4 can be a significant product of chloroethene biodegradation in some methanogenic sediments.