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21.
Some cyclic organo-chlorines share key characteristics to a significant degree, notably volatility, solubility in lipids, environmental persistence, a tendency to bioaccumulation, and toxicity to animals. A subset of this group has been designated "persistent organic pollutants" (POPs). Because of their volatility, persistence, and tendency to bioaccumulate, POPs are found in remote locations, such as the Arctic, far from the locations where they were initially used or produced.
Except PCDDs (dioxins) and PCDFs (furans), all are, or were, originally produced for use as such , mainly as pesticides or herbicides. PCDDs and PCDFs have never been produced for their own sake; they are unwanted contaminants of chemical intermediates that were passed on and incorporated in final products, notably herbicides; they are also generated spontaneously in most combustion processes and chlorine bleaching of paper. Most POPs have been sharply restricted or banned outright in most of the industrialized countries, but not in less developed countries.
The qualities of persistence and bioaccumulation give special urgency to monitoring not only point source emissions and local concentrations, but also the mobile environmental reservoirs and exposure routes of these chemicals. To conduct adequate risk analyses, far more detailed data is needed on quantities produced and used, quantities and location of storage, mode of use, location of use, and period of use. Such data are not collected consistently by government or international agencies. 相似文献
Except PCDDs (dioxins) and PCDFs (furans), all are, or were, originally produced for use as such , mainly as pesticides or herbicides. PCDDs and PCDFs have never been produced for their own sake; they are unwanted contaminants of chemical intermediates that were passed on and incorporated in final products, notably herbicides; they are also generated spontaneously in most combustion processes and chlorine bleaching of paper. Most POPs have been sharply restricted or banned outright in most of the industrialized countries, but not in less developed countries.
The qualities of persistence and bioaccumulation give special urgency to monitoring not only point source emissions and local concentrations, but also the mobile environmental reservoirs and exposure routes of these chemicals. To conduct adequate risk analyses, far more detailed data is needed on quantities produced and used, quantities and location of storage, mode of use, location of use, and period of use. Such data are not collected consistently by government or international agencies. 相似文献
22.
Anaerobic bacteria can reductively dehalogenate aliphatic and aromatic halogenated compounds in a respiratory process. Only a few of these bacteria have been isolated in pure cultures. However, long acclimation periods, substrate specificity, high dehalogenation rates, and the possibility to enrich for the dehalogenation activity by subcultivation in media containing an electron donor indicate that many of the reductive dehalogenations in the environment are catalyzed by specific bacteria. Molecular hydrogen or formate appear to be good electron donors for the enrichment of such organisms. Furthermore, systems have to be employed which supply the cultures with the halogenated compounds beyond their toxicity level. All bacteria that are presently available in pure culture and grow with a halogenated compound as electron acceptor are members of new genera. Based on experimental results with the membrane-impermeable electron mediator methyl viologen, a model of the respiration system ofDehalobacter restrictus, a tetrachloroethene-dechlorinating bacterium, is presented. Further studies of the biochemistry and energetics of respiratory-dehalogenating strains will help to understand the mechanisms involved and perhaps reveal the evolutionary origin of the dehalogenating enzyme systems.Abbreviations PCE
tetrachloroethene
- TCE
trichloroethene
-
cis-1,2-DCE
cis-1,2-dichloroethene
- PCER
tetrachloroethene reductase 相似文献
23.
An overview is presented of radicals generated on porous metal oxide surfaces such as zeolites whose main source of generation has been ionizing radiation. Attention is primarily paid to ESR studies on structures and reactions of organic neutral and ionic radicals. A short introduction is also given to paramagnetic metal ions and clusters formed in zeolites and other related materials. 相似文献
24.
. Chrzanowski L.Y. Wick R. Meulenkamp M. Kaestner H.J. Heipieper 《Letters in applied microbiology》2009,48(6):756-762
Aims: To investigate the effect of a mixture of rhamnolipid R1 and R2 biosurfactants produced by a Pseudomonas aeruginosa strain on the toxicity of phenol and chlorophenols to Pseudomonas putida DOT-T1E.
Methods and Results: Toxicity was quantified by the effective concentration 50% (EC50), that is the concentration that causes a 50% inhibition of bacterial growth. The presence of 300 mg l−1 rhamnolipids, that is at about twice their critical micelle concentration (CMC), increased the EC50 of phenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,5-trichlorophenol by about 12, 19, 32 and 40%, respectively, and consequently reduced the bioavailability and the freely dissolved concentration of the toxic phenolic compounds. The reduction was related to the phenols' octanol–water partition coefficients ( K ow ).
Conclusions: The reduction in toxicity of the phenols can be explained by a combination of toxin accumulation in biosurfactant micelles and hydrophobic interactions of the phenols with rhamnolipid-based dissolved organic carbon.
Significance and Impact of the Study: Results provide evidence that next to the effect of the micelle formation also hydrophobic interactions with rhamnolipid-based dissolved organic carbon affects the bioavailability of the phenols. Quantifying the effect of biosurfactants on the toxicity of hydrophobic compounds such as phenols thus appears to be a useful approach to assess their bioavailable equilibrium concentration. 相似文献
Methods and Results: Toxicity was quantified by the effective concentration 50% (EC50), that is the concentration that causes a 50% inhibition of bacterial growth. The presence of 300 mg l
Conclusions: The reduction in toxicity of the phenols can be explained by a combination of toxin accumulation in biosurfactant micelles and hydrophobic interactions of the phenols with rhamnolipid-based dissolved organic carbon.
Significance and Impact of the Study: Results provide evidence that next to the effect of the micelle formation also hydrophobic interactions with rhamnolipid-based dissolved organic carbon affects the bioavailability of the phenols. Quantifying the effect of biosurfactants on the toxicity of hydrophobic compounds such as phenols thus appears to be a useful approach to assess their bioavailable equilibrium concentration. 相似文献
25.
The anaerobic biodegradability and transformationof the mono-and dichlorinated salicylates(2-hydroxybenzoates) was examined under denitrifying,Fe (III) reducing, sulfate reducing andmethanogenic conditions. 3,6-Dichlorosalicylateand 6-chlorosalicylate are anaerobic microbialmetabolites of dicamba, a widely used herbicide.Anaerobic microcosms were established withdicamba treated soil from Wyoming, and golfcourse drainage stream sediments from NewJersey, which were each spiked with salicylate,3,6-dichlorosalicylate or one of the fourmonochlorosalicylate isomers. Salicylatewas degraded under denitrifying, sulfidogenic andmethanogenic conditions. In methanogenicenrichments 5-chlorosalicylate and 3-chlorosalicylatewere reductively dehalogenated to salicylatewhich was then utilized. Dehalogenation ofmonochlorinated salicylates to salicylate wasalso observed in denitrifying chlorosalicylatedegrading cultures. The study revealed thatthe position of the chlorine substituent as well as thepredominant electron accepting process affectthe rate and extent of chlorosalicylate degradationin anoxic environments. 相似文献
26.
Phytoscreening has been demonstrated at a variety of sites over the past 15 years as a low-impact, sustainable tool in delineation of shallow groundwater contaminated with chlorinated solvents. Collection of tree cores is rapid and straightforward, but low concentrations in tree tissues requires sensitive analytics. Solid-phase microextraction (SPME) is amenable to the complex matrix while allowing for solvent-less extraction. Accurate quantification requires the absence of competitive sorption, examined here both in laboratory experiments and through comprehensive examination of field data. Analysis of approximately 2,000 trees at numerous field sites also allowed testing of the tree genus and diameter effects on measured tree contaminant concentrations. Collectively, while these variables were found to significantly affect site-adjusted perchloroethylene (PCE) concentrations, the explanatory power of these effects was small (adjusted R2 = 0.031). 90th quantile chemical concentrations in trees were significantly reduced by increasing Henry's constant and increasing hydrophobicity. Analysis of replicate tree core data showed no correlation between replicate relative standard deviation (RSD) and wood type or tree diameter, with an overall median RSD of 30%. Collectively, these findings indicate SPME is an appropriate technique for sampling and analyzing chlorinated solvents in wood and that phytoscreening is robust against changes in tree type and diameter. 相似文献
27.
28.
Patrick K H Lee Dan Cheng Ping Hu Kimberlee A West Gregory J Dick Eoin L Brodie Gary L Andersen Stephen H Zinder Jianzhong He Lisa Alvarez-Cohen 《The ISME journal》2011,5(6):1014-1024
Comparative genomics of Dehalococcoides strains and an enrichment were performed using a microarray targeting genes from all available sequenced genomes of the Dehalococcoides genus. The microarray was designed with 4305 probe sets to target 98.6% of the open-reading frames from strains 195, CBDB1, BAV1 and VS. The microarrays were validated and applied to query the genomes of two recently isolated Dehalococcoides strains, ANAS1 and ANAS2, and their enrichment source (ANAS) to understand the genome–physiology relationships. Strains ANAS1 and ANAS2 can both couple the reduction of trichloroethene, cis-dichloroethene (DCE) and 1,1-DCE, but not tetrachloroethene and trans-DCE with growth, whereas only strain ANAS2 couples vinyl chloride reduction to growth. Comparative genomic analysis showed that the genomes of both strains are similar to each other and to strain 195, except for genes that are within the previously defined integrated elements or high-plasticity regions. Combined results of the two isolates closely matched the results obtained using genomic DNA of the ANAS enrichment. The genome similarities, together with the distinct chlorinated ethene usage of strains ANAS1, ANAS2 and 195 demonstrate that closely phylogenetically related strains can be physiologically different. This incongruence between physiology and core genome phylogeny seems to be related to the presence of distinct reductive dehalogenase-encoding genes with assigned chlorinated ethene functions (pceA, tceA in strain 195; tceA in strain ANAS1; vcrA in strain ANAS2). Overall, the microarrays are a valuable high-throughput tool for comparative genomics of unsequenced Dehalococcoides-containing samples to provide insights into their gene content and dechlorination functions. 相似文献
29.
30.
Patricia J. S. Colberg 《Geomicrobiology journal》2013,30(3-4):147-165
Despite recent progress made in describing microbial transformations that occur under anaerobic conditions, our understanding of the role sulfate‐reducing bacteria may play in the remediation of environmental contaminants is still very limited. The objective of this mini‐review is to summarize what is currently known of the metabolism of chlorinated aromatic compounds in the presence of sulfate. Sulfidogenic processes are discussed with respect to the thermodynamics of haloaromatic oxidation and to their potential use in the in situ bioremediation of hazardous organic wastes. A comprehensive listing is made of anaerobic transformations that involve both halogenated and nonhalogenated monoaromatic substrates by denitrifiers, dissimilatory iron‐reducing bacteria, and methanogenic consortia. In contrast to other anaerobic processes, studies involving sulfate‐mediated metabolism of hazardous organic compounds have been neglected; however, the recent success in defining methanogenic transformations, in particular, has enhanced expectations of defining an analogous role for sulfate‐reducing microbial communities in low redox environments that have become contaminated with hazardous substances. 相似文献