Dechlorination

Chlorinated solvents in groundwater pose threats to human health and the environment due to their carcinogenesis and bioaccumulation. These problems are often more severe in developing countries such as China. Thus, methods for chlorinated solvent-contaminated groundwater remediation are urgently needed. This study presents a technique of in situ remediation via the direct-push amendment injection that enhances the reductive dechlorination of chlorinated solvents in groundwater in the low-permeability aquifer...

Cis-1,2-dichloroethylene (cDCE), which is a common hazardous compound, often accumulates during incomplete reductive dechlorination of higher chlorinated ethenes (CEs) at contaminated sites. Simple monoaromatics, such as toluene and phenol, have been proven to induce biotransformation of cDCE in microbial communities incapable of cDCE degradation in the absence of other carbon sources. The goal of this microcosm-based laboratory study was to discover non-toxic natural monoaromatic secondary plant metabolites (SPMEs) that could enhance cDCE degradation in a similar manner to toluene and phenol...

Organohalide-respiring bacteria have key roles in the natural chlorine cycle; however, most of the current knowledge is based on cultures from contaminated environments. We demonstrate that grape pomace compost without prior exposure to chlorinated solvents harbors a Dehalogenimonas (Dhgm) species capable of using chlorinated ethenes, including the human carcinogen and common groundwater pollutant vinyl chloride (VC) as electron acceptors. Grape pomace microcosms and derived solid-free enrichment cultures were able to dechlorinate trichloroethene (TCE) to less chlorinated daughter products including ethene...

This report describes results of a bench-scale treatability study to evaluate the efficacy of bioaugmentation with bioamended activated carbon (AC) for in-situ treatment of polychlorinated biphenyl (PCB) impacted sediments. To this end, the ability of PCB transforming microorganisms to degrade and reduce the overall concentration of PCBs in sediment was determined in 2 L recirculating mesocosms designed to simulate conditions in Abraham's Creek in Quantico, Virginia. Ten sediment mesocosms were tested for the effects of AC alone, AC with slow release electron donor (cellulose) and different concentrations and combinations of PCB dehalogenating and degrading microorganisms added as bioamendments...

RATIONALE: Bacterial reductive dechlorination of the groundwater contaminant tetrachloroethene (PCE) involves the formation of lower chlorinated metabolites. Metabolites can be instantaneously formed and consumed in this sequential process; quantification and validation of their isotopic effects conventionally rely on separate laboratory microcosm studies. Here, we present an evaluation method enabling the determination of the carbon isotope enrichment factor (ε) for the intermediate cis-dichloroethene (cis-DCE) by a single laboratory microcosm study initially amending the precursor PCE only...

Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants that are distributed worldwide. Although industrial PCB production has stopped, legacy contamination can be traced to several different commercial mixtures (e.g., Aroclors in the USA). Despite their persistence, PCBs are subject to naturally occurring biodegradation processes, although the microbes and enzymes involved are poorly understood. The biodegradation potential of PCB-contaminated sediments in a wastewater lagoon located in Virginia (USA) was studied...

Aroclor 1254 (A1254) is the most toxic commercial PCB mixture produced, primarily due to its relatively high concentrations of dioxin-like congeners. This study demonstrates a comparative evaluation of dechlorination of A1254 and PCB-118 by indigenous organohalide respiring bacteria enriched from three PCB impacted sites: Grasse River (GR), NY; Fox River (FR), WI; and Baltimore Harbor (BH), MD. PCB-118 dechlorination rates in GR, BH, and FR was 0.0308, 0.015, and 0.0006 Cl(-)/biphenyl/day, respectively. A1254 dechlorination rates in GR, FR, and BH were 0...

Polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) are persistent organic pollutants whose main removal process in the environment is due to biodegradation, and particularly anaerobic reductive dechlorination. Since PCDD/F congeners that are substituted in the lateral 2, 3, 7, and 8 positions are the most toxic, removal of these chlorines is advantageous, but previous studies have only demonstrated their removal under laboratory conditions. We evaluated a concentration data set of PCDD/F congeners with four or more chlorines along with all 209 polychlorinated biphenyl (PCB) congeners in surface water, treated and untreated wastewater, landfill leachate, and biosolids (NY CARP dataset) to determine whether peri and peri/lateral dechlorination of PCDD/Fs occurs in these environments...

Iodotyrosine deiodinase (IYD) is unusual for its reliance on flavin and ability to promote reductive dehalogenation under aerobic conditions. As implied by the name, this enzyme was first discovered to catalyze iodide elimination from iodotyrosine for recycling iodide during synthesis of tetra- and triiodothyronine collectively known as thyroid hormone. However, IYD likely supports many more functions and has been shown to debrominate and dechlorinate bromo- and chlorotyrosines. A specificity for halotyrosines versus halophenols is well preserved from humans to bacteria...

Anaerobic reductive dechlorination is an important degradation pathway for chlorinated organic contaminants in paddy soil. This study investigated the effects of amending paddy soil with wheat straw biochar on both the dechlorination of hexachlorobenzene (HCB), a typical highly chlorinated contaminant, and on the structure of soil bacteria communities. Soil amendment of 0.1% biochar did not significantly affect the dechlorination of HCB in the soil. However, biochar amendment at higher application levels (5%) stimulated the dechlorination of HCB in the first month of anaerobic incubation and inhibited the dechlorination of HCB after that period...

10-Chloromethyl-11-demethyl-12-oxo-calanolide (F18), an analog of calanolide A, is a novel potent nonnucleoside reverse transcriptase inhibitor against HIV-1. Here, we report the metabolic profile and the results of associated biochemical studies of F18 in vitro and in vivo. The metabolites of F18 were identified based on liquid chromatography-electrospray ionization mass spectrometry and/or nuclear magnetic resonance. Twenty-three metabolites of F18 were observed in liver microsomes in vitro. The metabolism of F18 involved 4-propyl chain oxidation, 10-chloromethyl oxidative dechlorination and 12-carbonyl reduction...

Reactive transport modeling of multi-element, compound-specific isotope analysis (CSIA) data has great potential to quantify sequential microbial reductive dechlorination (SRD) and alternative pathways such as oxidation, in support of remediation of chlorinated solvents in groundwater. As a key step towards this goal, a model was developed that simulates simultaneous carbon, chlorine, and hydrogen isotope fractionation during SRD of trichloroethene, via cis-1,2-dichloroethene (and trans-DCE as minor pathway), and vinyl chloride to ethene, following Monod kinetics...

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0...

This paper investigates the feasibility of applying in-situ Bioremediation (ISB) to three sites contaminated with vinyl chloride and/or chlorinated alkanes such as 1,2-DCA and 1,1,2-TCA, presenting distinct hydrogeological settings and history of contaminant loading. Biotransformation of these compounds is well established in laboratory studies and pure cultures. Due to confidential aspects, however, few field data are available to support real case studies to the predictability of their fate and lifetime in soil and groundwater...

Fractionation of the bioactive CHCl3-MeOH (1:1) extracts obtained from two collections of the sponge consortium Plakortis symbiotica-Xestospongia deweerdtae from Puerto Rico provided two new plakinidone analogues, designated as plakinidone B (2) and plakinidone C (3), as well as the known plakinidone (1), plakortolide F (4), and smenothiazole A (5). The structures of 1-5 were characterized on the basis of 1D and 2D NMR spectroscopic, IR, UV, and HRMS analysis. The absolute configurations of plakinidones 2 and 3 were established through chemical correlation methods, VCD/ECD experiments, and spectroscopic data comparisons...

The acute toxicity of carbosulfan and chlorpyrifos in formulated pesticides to glochidia (larvae) of the freshwater mussel (Hyriopsis bialata Simpson, 1900) was evaluated under static conditions in moderately hard dechlorinated tap water. Measured pesticide concentrations were 26 to 34% lower than nominal concentrations; therefore, all results are expressed in terms of measured active ingredient. Carbosulfan was relatively non-toxic to the mussel larvae with median effective concentrations (EC50) of carbosulfan at 24 and 48 h greater than 0...

BACKGROUND: Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) plays a major role in detoxifying anoxic contaminated freshwater and marine sediments from PCBs. Known members of the phylum Chloroflexi are typically responsible for this activity in freshwater sediments, whereas less is known about the microorganisms responsible for this activity in marine sediments. PCB-respiring activities were detected in PCB-impacted marine sediments of the Venice Lagoon. The aim of this work was to identify the indigenous organohalide-respiring microorganisms in such environments and assess their dechlorination specificity against spiked Aroclor™ 1254 PCBs under laboratory conditions resembling the in situ biogeochemistry...

The widespread, persistent and toxic organophosphorus esters (OPEs) have become one category of emerging environmental contaminants. Thus, it is in urgent need to develop a cost-effective and safe treatment technology for OPEs control. The current study is a comprehensive attempt to use UV/TiO2 heterogeneous photocatalysis for the degradation of a water dissolved OPEs, tris(2-chloroethyl) phosphate (TCEP). A pseudo-first order degradation reaction with a kobs of 0.3167 min(-1) was observed, while hydroxyl radical may be the dominating reactive oxidative species...

We developed a novel stabilized nanoscale zerovalent iron (NZVI) particles with Ni using an electron conducting polymer, polyvinylpyrrolidone (PVP), to selectively dechlorinate trichloroethylene (TCE) to non-toxic intermediates. The size of the PVP stabilized NZVI-Ni ((PVP-NZVI-Ni), average diameter: ∼20nm) is smaller than that of bare NZVI (50-80nm) due to the prevention of agglomeration of the resultant iron particles by PVP. PVP-NZVI-Ni showed a complete removal of TCE in 1h with superior dechlorination kinetics (kobs=5...

Nocardioides sp. strain PD653 was the first aerobic bacterium capable of mineralizing hexachlorobenzene (HCB) that was identified. In this study, strain PD653-B2, which was unexpectedly isolated from a subculture of strain PD653, was found to lack the ability to transform HCB or pentachloronitrobenzene into pentachlorophenol. Comparative genome analysis of the two strains revealed that genetic rearrangement had occurred in strain PD653-B2, with a genomic region present in strain PD653 being deleted. In silico analysis allowed three open reading frames within this region to be identified as candidate genes involved in HCB dechlorination...