A Data Mining Approach to Predict In Situ Detoxification Potential of Chlorinated Ethenes

Despite advances in physicochemical remediation technologies, in situ bioremediation treatment based on <i>Dehalococcoides mccartyi</i> (<i>Dhc</i>) reductive dechlorination activity remains a cornerstone approach to remedy sites impacted with chlorinated ethenes. Selecting the best remedial strategy is challenging due to uncertainties and complexity associated with biological and geochemical factors influencing <i>Dhc</i> activity. Guidelines based on measurable biogeochemical parameters have been proposed, but contemporary efforts fall short of meaningfully integrating the available information. Extensive groundwater monitoring data sets have been collected for decades, but have not been systematically analyzed and used for developing tools to guide decision-making. In the present study, geochemical and microbial data sets collected from 35 wells at five contaminated sites were used to demonstrate that a data mining prediction model using the classification and regression tree (CART) algorithm can provide improved predictive understanding of a site’s reductive dechlorination potential. The CART model successfully predicted the 3-month-ahead reductive dechlorination potential with 75.8% and 69.5% true positive rate (i.e., sensitivity) for the training set and the test set, respectively. The machine learning algorithm ranked parameters by relative importance for assessing in situ reductive dechlorination potential. The abundance of <i>Dhc</i> 16S rRNA genes, CH₄, Fe²⁺, NO₃^–, NO₂^–, and SO₄^2– concentrations, total organic carbon (TOC) amounts, and oxidation–reduction potential (ORP) displayed significant correlations (<i>p</i> < 0.01) with dechlorination potential, with NO₃^–, NO₂^–, and Fe²⁺ concentrations exhibiting precedence over other parameters. Contrary to prior efforts, the power of data mining approaches lies in the ability to discern synergetic effects between multiple parameters that affect reductive dechlorination activity. Overall, these findings demonstrate that data mining techniques (e.g., machine learning algorithms) effectively utilize groundwater monitoring data to derive predictive understanding of contaminant degradation, and thus have great potential for improving decision-making tools. A major need for realizing the predictive capabilities of data mining approaches is a curated, open-access, up-to-date and comprehensive collection of biogeochemical groundwater monitoring data

Environmental Fate of the Next Generation Refrigerant 2,3,3,3-Tetrafluoropropene (HFO-1234yf)

The hydrofluoroolefin 2,3,3,3-tetrafluoropropene (HFO-1234yf) has been introduced to replace 1,1,1,2-tetrafluoroethane (HFC-134a) as refrigerant in mobile, including vehicle, air conditioning systems because of its lower global warming potential. HFO-1234yf is volatile at ambient temperatures; however, high production volumes and widespread handling are expected to release this fluorocarbon into terrestrial and aquatic environments, including groundwater. Laboratory experiments explored HFO-1234yf degradation by (i) microbial processes under oxic and anoxic conditions, (ii) abiotic processes mediated by reactive mineral phases and zerovalent iron (Fe⁰, ZVI), and (iii) cobalamin-catalyzed biomimetic transformation. These investigations demonstrated that HFO-1234yf was recalcitrant to microbial (co)­metabolism and no transformation was observed in incubations with ZVI, makinawite (FeS), sulfate green rust (GR_SO4), magnetite (Fe₃O₄), and manganese oxide (MnO₂). Sequential reductive defluorination of HFO-1234yf to 3,3,3-trifluoropropene and 3,3-dichloropropene with concomitant stoichiometric release of fluoride occurred in incubations with reduced cobalamins (e.g., vitamin B₁₂) indicating that biomolecules can transform HFO-1234yf at circumneutral pH and at ambient temperature. Taken together, these findings suggest that HFO-1234yf recalcitrance in aquifers should be expected; however, HFO-1234yf is not inert and a biomolecule may mediate reductive transformation in low redox environments, albeit at low rates

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

Contaminant discharge from fractured bedrock formations remains a remediation challenge. We applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C₁–C₃ chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of known dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinated C₁–C₃ alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but <i>Dehalococcoides</i> and <i>Dehalobacter</i> were more abundant in deeper sediment, where 5.7 ± 0.4 × 10⁵ and 5.4 ± 0.9 × 10⁶ 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock–sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation

Identification of 4‑Hydroxycumyl Alcohol As the Major MnO₂‑Mediated Bisphenol A Transformation Product and Evaluation of Its Environmental Fate

Bisphenol A (BPA), an environmental contaminant with weak estrogenic activity, resists microbial degradation under anoxic conditions but is susceptible to abiotic transformation by manganese dioxide (MnO₂). BPA degradation followed pseudo-first-order kinetics with a rate constant of 0.96 (±0.03) min^–1 in the presence of 2 mM MnO₂ (0.017% w/w) at pH 7.2. 4-hydroxycumyl alcohol (HCA) was the major transformation product, and, on a molar basis, up to 64% of the initial amount of BPA was recovered as HCA. MnO₂ was also reactive toward HCA, albeit at 5-fold lower rates, and CO₂ evolution (i.e., mineralization) occurred. In microcosms established with freshwater sediment, HCA was rapidly biodegraded under oxic, but not anoxic conditions. With a measured octanol–water partition coefficient (Log <i>K</i>_ow) of 0.76 and an aqueous solubility of 2.65 g L^–1, HCA is more mobile in saturated media than BPA (Log <i>K</i>_ow = 2.76; aqueous solubility = 0.31 g L^–1), and therefore more likely to encounter oxic zones and undergo aerobic biodegradation. These findings corroborate that BPA is not inert under anoxic conditions and suggest that MnO₂-mediated coupled abiotic–biotic processes may be relevant for controlling the fate and longevity of BPA in sediments and aquifers

Quantifying the Effects of 1,1,1-Trichloroethane and 1,1-Dichloroethane on Chlorinated Ethene Reductive Dehalogenases

Mixtures of chlorinated ethenes and ethanes are often found at contaminated sites. In this study, we undertook a systematic investigation of the inhibitory effects of 1,1,1-trichloroethane (1,1,1-TCA) and 1,1-dichloroethane (1,1-DCA) on chlorinated ethene dechlorination in three distinct <i>Dehalococcoides</i>-containing consortia. To focus on inhibition acting directly on the reductive dehalogenases, dechlorination assays used cell-free extracts prepared from cultures actively dechlorinating trichloroethene (TCE) to ethene. The dechlorination assays were initiated with TCE, <i>cis</i>-1,2<i>-</i>dichloroethene (cDCE), or vinyl chloride (VC) as substrates and either 1,1,1-TCA or 1,1-DCA as potential inhibitors. 1,1,1-TCA inhibited VC dechlorination similarly in cell suspension and cell-free extract assays, implicating an effect on the VC reductases associated with the dechlorination of VC to nontoxic ethene. Concentrations of 1,1,1-TCA in the range of 30–270 μg/L reduced VC dechlorination rates by approximately 50% relative to conditions without 1,1,1-TCA. 1,1,1-TCA also inhibited reductive dehalogenases involved in TCE and cDCE dechlorination. In contrast, 1,1-DCA had no pronounced inhibitory effects on chlorinated ethene reductive dehalogenases, indicating that removal of 1,1,1-TCA via reductive dechlorination to 1,1-DCA is a viable strategy to relieve inhibition

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

Contaminant discharge from fractured bedrock formations remains a remediation challenge. We applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C₁–C₃ chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of known dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinated C₁–C₃ alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but <i>Dehalococcoides</i> and <i>Dehalobacter</i> were more abundant in deeper sediment, where 5.7 ± 0.4 × 10⁵ and 5.4 ± 0.9 × 10⁶ 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock–sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

Contaminant discharge from fractured bedrock formations remains a remediation challenge. We applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C₁–C₃ chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of known dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinated C₁–C₃ alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but <i>Dehalococcoides</i> and <i>Dehalobacter</i> were more abundant in deeper sediment, where 5.7 ± 0.4 × 10⁵ and 5.4 ± 0.9 × 10⁶ 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock–sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

Contaminant discharge from fractured bedrock formations remains a remediation challenge. We applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C₁–C₃ chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of known dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinated C₁–C₃ alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but <i>Dehalococcoides</i> and <i>Dehalobacter</i> were more abundant in deeper sediment, where 5.7 ± 0.4 × 10⁵ and 5.4 ± 0.9 × 10⁶ 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock–sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation