Anaerobic Biodegradation of Alkylbenzenes in Laboratory Microcosms Representing Ambient Conditions

A microcosm study was performed to document the anaerobic biodegradation of benzene, toluene, ethylbenzene, m- xylene, and/or o-xylene in petroleum-contaminated aquifer sediment from sites in Michigan (MI) and North Carolina (NC) and relate the results to previous field investigations of intrinsic bioremediation. Laboratory microcosms, designed to simulate ambient conditions, were constructed under anaerobic conditions with sediment and groundwater from source, mid-plume, and end-plume locations at each site. The general patterns of biodegradation and electron acceptor utilization in the microcosms were consistent with field data. At the MI site, methane was produced after a moderate lag period, followed by toluene degradation in all sets of microcosms. At the NC site, biodegradation of the target compounds was not evident in the source area microcosms. In the mid-plume microcosms, toluene and o-xylene biodegraded first, followed by m-xylene and benzene, a pattern consistent with contaminant decay along the plume length. Chemical extraction of microcosm sediment at the beginning and end of me incubation indicated that iron-reducing conditions were dominant and iron reduction occurred on a sediment fraction not extracted by 0.5N HC1. In the end-plume microcosms, degradation of benzene, toluene, and xylene isomers occurred but was variable between replicates. Consistent with field data, dissolved concentrations of the target contaminant(s) persisted at low but detectable levels (0.05 to 0.25 μM) in microcosms from both sites where biodegradation was measured.     

In situ bioremediation of monoaromatic pollutants in groundwater: a review

Monoaromatic pollutants such as benzene, toluene, ethylbenzene and mixture of xylenes are now considered as widespread contaminants of groundwater. In situ bioremediation under natural attenuation or enhanced remediation has been successfully used for removal of organic pollutants, including monoaromatic compounds, from groundwater. Results published indicate that in some sites, intrinsic bioremediation can reduce the monoaromatic compounds content of contaminated water to reach standard levels of potable water. However, engineering bioremediation is faster and more efficient. Also, studies have shown that enhanced anaerobic bioremediation can be applied for many BTEX contaminated groundwaters, as it is simple, applicable and economical.

This paper reviews microbiology and metabolism of monoaromatic biodegradation and in situ bioremediation for BTEX removal from groundwater under aerobic and anaerobic conditions. It also discusses the factors affecting and limiting bioremediation processes and interactions between monoaromatic pollutants and other compounds during the remediation processes.     

Selecting Remediation Goals by Assessing the Natural Attenuation Capacity of Groundwater Systems

Remediation goals for the source areas of a chlorinated ethene-contaminated groundwater plume were identified by assessing the natural attenuation capacity of the aquifer system. The redox chemistry of the site indicates that sulfate-reducing (H₂ ∼ 2 nanomoles [nM]) per liter conditions near the contaminant source grade to Fe(III)-reducing conditions (H₂ ∼ 0.5 nM) downgradient of the source. Sulfate-reducing conditions facilitate the initial reduction of perchloroethene (PCE) to trichloroethene (TCE), cis-dichloroethene (cis-DCE), and vinyl chloride (VC). Subsequently, the Fe(III)-reducing conditions drive the oxidation of cis-DCE and VC to carbon dioxide and chloride. This sequence gives the aquifer a substantial capacity for biodegrading chlorinated ethenes. Natural attenuation capacity (the slope of the steady-state contaminant concentration profile along a groundwater flowpath) is a function of biodegradation rates, aquifer dispersive characteristics, and groundwater flow velocity. The natural attenuation capacity at the Kings Bay, Georgia site was assessed by estimating groundwater flowrates (∼0.23±0.12 m/d) and aquifer dispersivity (∼1 m) from hydrologic and scale considerations. Apparent biodegradation rate constants (PCE and TCE ∼0.01 d^-1; cis-DCE and VC ∼0.025 d^-1) were estimated from observed contaminant concentration changes along aquifer flowpaths. A boundary-value problem approach was used to estimate levels to which contaminant concentrations in the source areas must be lowered (by engineered removal), or groundwater flow velocities lowered (by pumping) for the natural attenuation capacity to achieve maximum concentration limits (MCLs) prior to reaching a predetermined regulatory point of compliance.     

Controlled Field Study on the Use of Nitrate and Oxygen for Bioremediation of a Gasoline Source Zone

Controlled releases of unleaded gasoline were used to evaluate the biotransformation of the soluble aromatic hydrocarbons (benzene, toluene, ethylbenzene, xylene isomers, trimethylbenzene isomers, and naphthalene) within a source zone using nitrate and oxygen as electron acceptors. Experiments were performed within two 2 m×2 m×3.5 m deep sheet-piling cells. A gasoline-contaminated zone was created below the water table in each treatment cell. Groundwater amended with electron acceptors was then flushed continuously through the cells for 174 d. One cell received approximately 100 mg/L nitrate and “microaerophilic” (i.e., 2 mg/L or less) dissolved oxygen (DO), a second cell received micro aerophilic DO only. Electron-acceptor utilization and hydrocarbon-metabolite formation were observed in both cells, suggesting that some microbial activity had been induced in response to flushing. However, nitrate utilization was slow relative to the cell residence time, and aromatic-hydrocarbon mass losses in response to microaerophilic DO addition were not apparent under these in situ conditions. Concentration trends in both cells suggested that there was relatively little biotransformation of the aromatic hydrocarbons over the 2-m flow path monitored in this experiment. Extraction-well concentration trends, for example, were consistent with abiotic gasoline dissolution. The results from the nitrate-amended cell suggest that a large denitrifying population capable of aromatic hydrocarbon biotransformation failed to develop within the gasoline source zone over a 14-month period of nitrate exposure. This study reinforces the need for detailed aquifer-specific testing prior to selecting bioremediation for full-scale cleanup, particularly for recent hydrocarbon spills.     

Absorption and retention of selenium from shrimps in man

This study was undertaken to evaluate the bioavailability of selenium in shrimps, a possible good source of selenium, by measurements of the absorption and retention of selenium and the effects on plasma selenium concentration and glutathione peroxidase activity. Twelve healthy young subjects (9F and 3M) received 100 g of shrimps each day for six weeks in addition to their habitual diet. In the third week of the study a balance period was inserted in which the subjects received all food from the department and collected faeces and urine over 5 days. Blood samples were collected at commencement of the study, after 2, 4, and 6 weeks. The selenium intake increased from 39.4 ± 15.3 μg/d to 127 ± 5.5 μg/d with the addition of shrimps. The apparent absorption of selenium from shrimps was 83 ± 4%. Faecal and urinary selenium excretion was 32.5 ± 17.0 μg/d and 21.2 ± 9.0 μg/d, respectively and the total retention of selenium was 3.1 ± 1.1 mg. Plasma selenium concentrations were 95.2 ± 9.7 μg/L and 101.5 ± 9.7 μg/L before and after six weeks of shrimp intake, respectively (p<0.05). Plasma and erythrocyte glutathione peroxidase activities were not influenced by shrimp intake. Thus, despite the high absorption and retention, plasma selenium concentrations were only moderately affected by an increase in selenium intake of about 100 μg/d in the chemical forms found in shrimp. Whether the accumulation of selenium from shrimps in tissues may represent a potential hazard is to be further investigated.     

Biodegradation of Trichloroethylene and Its Anaerobic Daughter Products in Freshwater Wetland Sediments

The wide range of redox conditions and diversity of microbial populations in organic-rich wetland sediments could enhance biodegradation of chlorinated solvents. To evaluate potential biodegradation rates of trichloroethylene (TCE) and its anaerobic daughter products (cis-1,2-dichloroethylene; trans-1,2-dichloroethylene; and vinyl chloride), laboratory microcosms were prepared under methanogenic, sulfate-reducing, and aerobic conditions using sediment and groundwater from a freshwater wetland that is a discharge area for a TCE contaminant plume. Under methanogenic conditions, biodegradation rates of TCE were extremely rapid at 0.30 to 0.37 d^-1 (half-life of about 2 days). Although the TCE biodegradation rate was slower under sulfate-reducing conditions (0.032 d^-1) than under methanogenic conditions, the rate was still two orders of magnitude higher than those reported in the literature for microcosms constructed with sandy aquifer sediments. In the aerobic microcosm experiments, biodegradation occurred only if methane consumption occurred, indicating that methanotrophs were involved. Comparison of laboratory-measured rates indicates that production of the 1,2-dichloroethylene isomers and vinyl chloride by anaerobic TCE biodegradation could be balanced by their consumption through aerobic degradation where methanotrophs are active in wetland sediment. TCE degradation rates estimated using field data (0.009 to 0.016 d^-1) agree with the laboratory-measured rates within a factor of 3 to 22, supporting the feasibility of natural attenuation as a remediation method for contaminated groundwater discharging in this wetland and other similar environments.     

Effect of Chemical Oxidation on Subsurface Microbiology and Trichloroethene (TCE) Biodegradation

Research was conducted to determine the effect of chemical oxidation on subsurface microbiology and cometabolic biodegradation capacity in a trichloroethene (TCE)/perchloroethene (PCE)-contaminated aquifer previously treated with Fenton's reagent. Groundwater pH declined from 5 to 2.4 immediately after the treatment, and subsequently rose to a range of 3.4 to 4.0 after 17 months. Limited microbial growth and TCE degradation were detected in the treated zone (pH 3.37 and TCE 5 to 21 mg/L) with carbon addition (i.e., methane and phenol). Methane addition resulted in the enrichment of yeast and fungi in microcosms at low pH. In contrast, methane addition to groundwater from the control well (pH 4.9 and TCE ca. 0.7 mg/L) stimulated methanotrophic growth, indicated by methane consumption, fluorescent antibody analysis, phospholipid-based markers, and rDNA probes. TCE degradation was measured in the control microcosms, but only when phenol was added. Although higher TCE concentrations in the treated zone might have inhibited TCE cometabolism, these results also indicate that low groundwater pH resulting from the chemical oxidation process (pH 3.37 versus 4.9) inhibited TCE degradation. Methanotrophic growth and TCE biodegradation may be possible as pH increases both in the treated zone and at the leading edge of plume, as long as the local soil is able to buffer the groundwater pH. Moreover, the Fenton's reagent process could be designed to operate at a higher pH (e.g., ≥ 4.5) and/or lower hydrogen peroxide concentration to minimize detrimental effects, providing an optimal environment to couple advanced oxidation processes with bioremediation technologies.     

Effects of Oxygenation on Hydrocarbon Biodegradation in a Hypoxic Environment

In 1984, an underground storage tank leaked approximately 41,000 L of gasoline into the ground water at the Naval Construction Battalion Command in Port Hueneme, CA (USA). Benzene, toluene, ethylbenzene, and xylenes (BTEX) contamination stimulated remedial action. In 1995, a ground water circulation well (GCW) and network of surrounding monitoring wells were installed. After year of operation, dissolved oxygen and nitrate concentrations remained low in all monitoring wells. Benzene utilization (the sum of respiration, uptake, and conversion to polar compounds) ranged from 0.03 to 4.6 µg L^-1 h^-1, and toluene utilization ranged from 0.01 to 5.2 µg L^-1 h^-1. Heterotrophic bacterial productivity (total carbon assimilation) increased dramatically in the GCW, although benzene and toluene utilization decreased markedly relative to surrounding wells. Benzene and toluene uptake accounted for a significant proportion (mean=22%) of the heterotrophic bacterial productivity except within the GCW, indicating other fuel contaminant or indigenous organic carbon and not BTEX compounds served as primary carbon source. The GCW effectively air-stripped BTEX compounds, but failed to stimulate benzene and toluene biodegradation and thus would not be effective for stimulating BTEX bioremediation under current deployment parameters. Air stripping was three orders of magnitude more effective than biodegradation for removing benzene and toluene in the GCW.     

Production d'NH4 par la crevette Crangon crangon L. dans deux écosystémes côtiers. approche expérimentale et étude de l'influence du sédiment sur le taux d'excrétion

Estimation of the ammonia production of the shrimp C. crangon in two littoral ecosystems (oligotrophic sand and eutrophic mud) was determined in winter and summer conditions from laboratory observations in experimental microcosms. The ammonia excretion rate of C. crangon was not influenced by either the sediment type or the ammonia concentration of the overlying water; on the other hand, the mean excretion rate and the response to initial handling stress increased markedly as shrimp were deprived of soft substratum.

The daily ammonia production of C. crangon was 16 μmol NH₃ · g ⁻¹ wet wt · day ⁻¹ in winter and 40 μmol in summer. A gross production of 12 μmol NH₃ · m⁻² · day ⁻¹ and 300–700 μmol μ m⁻² · day⁻¹, respectively, could be expected in the two ecosystems studied. This would account for 5% (winter) and 2–4% (summer) of the total NH⁺₄ flux at the sediment-water interface. The contribution of the excretion of all macrofauna to the NH⁺₄ flux from the sediment is discussed.     

Use of an SF6-Based Diagnostic Tool for Assessing Air Distributions and Oxygen Transfer Rates during IAS Operation

A diagnostic test designed to assess air distribution and oxygen delivery rate to the aquifer during in situ air sparging (IAS) is described. The conservative tracer gas, sulfur hexafluoride (SF₆), is added upstream of the air injection manifold during steady IAS operation and groundwater samples are collected from the target treatment zone after some time period (usually 4 to 24 h). The appearance of SF₆ in groundwater is used to characterize the air distribution in the target treatment zone, while the SF₆ concentration increase with time is used to assess oxygen transfer rates to the target treatment zone. Conversion from SF₆ concentration to oxygen mass transfer rate involves correcting the SF₆ concentration increase over time for differences in the relevant chemical properties and injection air concentration. Data presented from a field demonstration site illustrate the utility of this test for identifying air distribution details not readily identified by deep vadose zone helium and groundwater pressure transducer response tests. Oxygen transfer rates at this site ranged from 0 to 20 mg-O₂/L-H₂O/d. Finally, a comparison of short-term SF₆ test data with longer-term dissolved oxygen data illustrated this test's utility for anticipating long-term dissolved oxygen distributions.     

Interactive effects of pH, arsenic and phosphorus on uptake of As and P and growth of the arsenic hyperaccumulator Pteris vittata L. under hydroponic conditions

Arsenic (As)-contaminated soil and water vary with pH and concentrations of As and P. This study examined the effects and interactions of three factors, pH, As and P, on As hyperaccumulator Pteris vittata L. to optimize plant growth and maximize As removal from contaminated sites, especially water. Two sets of hydroponic experiments were conducted using three-factor, five-level central composite design. Five levels of pH (4.5–8.0), As (0–668 μM), and P (0–1000 μM) were used to understand their individual as well as interactive effects. Plant biomass and uptake of P and As were impacted by all the three factors. Phosphorus inhibited As uptake at all concentrations, whereas As below 334 μM benefited plant growth and P uptake. Enhanced plant biomass was most likely a result of increased P uptake. Low pH enhanced plant uptake of As (pH≤5.21) and P (pH≤6.25). The fern had a relatively high biomass and P uptake at low pH/low As or high pH/high As. The referencing saddle points (turning points) were pH 6.33 and As 359 μM for plant biomass and pH 5.87 and As 331 μM for P uptake based on the response surface plot. The results suggested that optimum plant growth could be achieved by adjusting pH corresponding to As levels in the growth media, and maximum plant As hyperaccumulation by maintaining minimum P concentrations with medium pH≤5.21. Our results should be useful for developing strategies to remediate As-contaminated water using Chinese Brake fern.     

Effects of creosote compounds on the aerobic bio-degradation of benzene

The inhibitory effect of creosote compounds on the aerobic degradation of benzene was studied in microcosm experiments. A total removal of benzene was observed after twelve days of incubation in microcosms where no inhibition was observed. Thiophene and benzothiophene, two heterocyclic aromatic compounds containing sulfur (S-compounds), had a significant inhibitory effect on the degradation of benzene, but also an inhibitory effect of benzofuran (an O-compound) and 1-methylpyrrole (a N-compound) could be observed, although the effect was weaker. The NSO-compounds also had an inhibitory effect on the degradation of p-xylene, o-xylene, and naphthalene, while they only had a weak influence on the degradation of 1-methylnaphthalene, o-cresol and 2,4-dimethylphenol. The phenolic compounds seemed to have a weak stimulating effect on the degradation of benzene whereas the monoaromatic hydrocarbons and the naphthalenes had no significant influence on the benzene degradation. The inhibitory effect of the NSO-compounds on the aerobic degradation of benzene could be identified as three different phenomena. The lag phase increased, the degradation rate decreased, and a residual concentration of benzene was observed in microcosms when NSO-compounds were present. The results show that NSO-compounds can have a potential inhibitory effect on the degradation of many creosote compounds, and that inhibitory effects in mixtures can be important for the degradation of different compounds.Abbreviations ben benzene - bf benzofuran - bt benzothiophene - dmp 2,4-dimethylphenol - GC gas chromatograph - ind indole - mnap 1-methylnaphthalene - MAHs monoaromatic hydrocarbons - mp 1-methylpyrrole - nap naphthalene - NSO-compounds heterocyclic aromatic compounds containing nitrogen, sulphur or oxygen - o-cre o-cresol - o-xyl o-xylene - PAHs polyaromatic hydrocarbons - phe phenol - p-xyl p-xylene - pyr pyrrole - thi thiophene - qui quinoline     

Effects of creosote compounds on the aerobic bio-degradation of benzene

The inhibitory effect of creosote compounds on the aerobic degradation of benzene was studied in microcosm experiments. A total removal of benzene was observed after twelve days of incubation in microcosms where no inhibition was observed. Thiophene and benzothiophene, two heterocyclic aromatic compounds containing sulfur (S-compounds), had a significant inhibitory effect on the degradation of benzene, but also an inhibitory effect of benzofuran (an O-compound) and 1-methylpyrrole (a N-compound) could be observed, although the effect was weaker. The NSO-compounds also had an inhibitory effect on the degradation of p-xylene, o-xylene, and naphthalene, while they only had a weak influence on the degradation of 1-methylnaphthalene, o-cresol and 2,4-dimethylphenol. The phenolic compounds seemed to have a weak stimulating effect on the degradation of benzene whereas the monoaromatic hydrocarbons and the naphthalenes had no significant influence on the benzene degradation. The inhibitory effect of the NSO-compounds on the aerobic degradation of benzene could be identified as three different phenomena. The lag phase increased, the degradation rate decreased, and a residual concentration of benzene was observed in microcosms when NSO-compounds were present. The results show that NSO-compounds can have a potential inhibitory effect on the degradation of many creosote compounds, and that inhibitory effects in mixtures can be important for the degradation of different compounds.     

The activities of several detoxication enzymes are differentially induced by juices of garden cress, water cress and mustard in human HepG2 cells

It has been previously demonstrated in a human-derived hepatoma cell line (HepG2) that juices from cruciferous vegetables protect against the genotoxicity caused by dietary carcinogens. HepG2 cells possess different enzymes involved in the biotransformation of xenobiotics. Therefore, we investigated the effect of cruciferous juices on the activities of CYP 1A and several phase II enzymes in this cell model. For each experiment, 1 × 10⁶ cells were seeded on Petri dishes. After 2 days, the juices (0.5–8 μl/ml of culture medium) were added for 48 h prior to cell harvesting. The addition of juice from water cress (Nasturtium officinalis R. Br) significantly increased the activities of ethoxyresorufin-O-deethylase at high doses only and NAD(P)H-quinone reductase in a dose-dependent manner (1.8- and 5-fold, respectively). The addition of juice from garden cress (Lepidum sativum L.) significantly increased the activities of NAD(P)H-quinone reductase and UDP-glucuronosyl-transferase with a maximal effect around the dose of 2 μl/ml juice (1.4- and 1.2-fold, respectively) while the other enzymes were not altered. Mustard (Sinapis alba L.) juice increased the activities of NAD(P)H-quinone reductase (2.6-fold at the dose of 8 μl/ml), and N-acetyl-transferase (1.4-fold at the dose of 8 μl/ml) in a dose-dependent manner while a maximal induction of UDP-glucuronosyl-transferase was obtained with a dose of 2 μl/ml (1.8-fold). These observations show that the three juices have different induction profiles: only water cress acted as a bifunctional inducer by enhancing both phase I and phase II enzymes. As a consequence, each juice may preferentially inhibit the genotoxicity of specific compounds.     

The impact of long-term past exposure to elemental mercury on antioxidative capacity and lipid peroxidation in mercury miners

Limited information is available on the effects of chronic mercury exposure in relation to the risk of cardiovascular disease (CVD). It is known from in vitro and in vivo studies that Hg can promote lipid peroxidation through promotion of free radical generation, and interaction with antioxidative enzymes and reduction of bioavailable selenium. The objective of the study was to test the hypothesis that long-term past occupational exposure to elemental Hg (Hg⁰) can modify antioxidative capacity and promote lipid peroxidation in miners.

The study population comprised 54 mercury miners and 58 workers as the control group. The miners were examined in the post-exposure period. We evaluated their previous exposure to Hg⁰, the putative appearance of certain nonspecific symptoms and signs of micromercurialism, as well as the main behavioural and biological risk factors for CVD, and determined: 1) Hg and Se levels in blood and urine, 2) antioxidative enzymes, Cu/Zn superoxide dismutase (CuZn-SOD), catalase (CAT), and selenoenzyme glutathione peroxidase (GSH-Px) activity in erythrocytes as indirect indices of free radical activity, 3) pineal hormone melationin (MEL) in blood and urine, and 4) lipid hydroperoxides (LOOHs) and malondialdehyde (MDA) as lipid peroxidation products.

The mercury miners were intermittently exposed to Hg⁰ for periods of 7 to 31 years. The total number of exposure periods varied from 13 to 119. The cumulative U-Hg peak level varied from 794-11,365 μg/L. The current blood and urine Hg concentrations were practically on the same level in miners and controls. Miners showed some neurotoxic and nephrotoxic sequels of micromercurialism. No significant differences in behavioural and biological risk factors for CVD were found between miners and controls. A weak correlation (r = 0.36, p < 0.01) between systolic blood pressure and average past exposure U-Hg level was found. The mean P-Se in miners (71.4 μg/L) was significantly lower (p < 0.05) than in the controls (77.3 μg/L), while the mean U-Se tended to be higher (p < 0.05) in miners (16.5 μg/g creatinine) than in the controls (14.0 μg/g creatinine). Among antioxidative enzyme activities, only CAT in erythrocytes was significantly higher (p < 0.01) in miners (3.14 MU/g Hb) than in the controls (2.65 MU/g Hb). The mean concentration of B-MEL in miners (44.3 ng/L) was significantly higher (p < 0.01) than in the controls (14.9 ng/L). The mean value of U-MEL sulphate (31.8 μg/L) in miners was significantly lower (p < 0.01) than in the control group (46.9 μg/L). Among the observed lipid peroxidative products, the mean concentration of U-MDA was statistically higher (p < 0.01) in miners (0.21 μmol/mmol creatinine) than in the controls (0.17 μmol/mmol creatinine).

In the group of miners with high mercury accumulation and the presence of some nonspecific symptoms and signs of micromercurialism, the results of our study partly support the assumption that long-term occupational exposure to Hg⁰ enhances the formation of free radicals even several years after termination of occupational exposure. Therefore, long-term occupational exposure to Hg⁰ could be one of the risk factors for increased lipid peroxidation and increased mortality due to ischaemic heart disease (ICH) found among the mercury miners of the Idrija Mine.     

Vapor Pressure Characterization to Predict Contaminant Releases from MGP Site Source Area Soils

Risk-based management of contaminated sites often requires timely screening and identification of source areas that release contaminants to groundwater and other reception of concern. Over-reliance on total concentrations often results in costly site characterization, delays in remediation, and overestimation of the soil volumes targeted for removal or treatment. Advances in diagnostic tools to accelerate source area characterization will improve the reliability of management decisions. The objective of this work was to determine the potential of using vapor pressure measurements as a rapid indicator of the mass release potential of suspected source area soils.

The current work has focused on determining the relationship between partial pressure and mobility for monoaromatic and polycyclic aromatic hydrocarbon (PAH) contaminants in source area soils. This work ascertained that for a wide spectrum of non-ionized, aromatic contaminants in MGP soils, total vapor pressure and benzene partial pressure could be measured with good repeatability. Under controlled conditions, photoionization detector (PID) measurements on 16 soil samples from two MGP sites were found to correlate well to laboratory measurements of equilibrium partitioning and resin-mediated soil contaminant desorption with R² values of over 0.9. Results indicate that vapor pressure correlates well to contaminant mobility in soils.     

Chemistry of vinylidene complexes XI. Synthesis of trinuclear MnFePt complexes by means of consecutive assembling out of mono- and dimetal vinylidene precursors

The dimetal μ-vinylidene complexes Cp(CO)₂MnPt(μ-C = CHPh)L₂ (L = tert.-phosphine or -phosphite), which have been obtained by coupling of the mononuclear complex Cp(CO)₂Mn=C=CHPh and unsaturated PtL₂ unit, add smoothly the Fe(CO)₄ moiety to produce trimetal MnFePt compounds. The μ₃-vinylidene cluster CpMnFePt(μ₃-C=CHPh)(CO)₆(PPh₃) was prepared in quantitative yields from the reactions of Cp(CO)₂MnPt(μ-C=CHPh)(PPh₃)L (L = PPh₃ or CO) with Fe₂(CO)₉ in benzene at 20 °C. The phosphite-substituted complexes Cp(CO)₂Mnpt(μ-C=CHPh)L₂ (L = P(OEt)₃ or P(OPrⁱ)₃) react under analogous conditions with Fe₂(CO)₉ to give mixtures (2:3) of the penta- and hexacarbonyl clusters, CpMnFePt(μ₃-C = CHPh)(CO)₅L₂ and CpMnFePt(μ₃-C = CHPh)(CO)₆L, respectively. The similar reaction of the dimetal complex Cp(CO)₂MnPt(μ-C = CHPh)(dppm), in which the Pt atom is chelated by dppm = Ph₂PCH₂PPhPin2 ligand, gives only a 15% yield of the analogous trimetal μ₃-vinylidene hexacarbonyl product CpMnFePt(μ₃-C = CHPh)(CO)(dppm), but the major product (40%) is the tetranuclear μ₄-vinylidene cluster (dppm)PtFe₃(μ₄-C = CHPh)(CO)₉. The IR and ¹H, ¹³C and ³¹P NMR data for the new complexes are reported and discussed.     

Novel aerobic benzene degrading microorganisms identified in three soils by stable isotope probing

The remediation of benzene contaminated groundwater often involves biodegradation and although the mechanisms of aerobic benzene biodegradation in laboratory cultures have been well studied, less is known about the microorganisms responsible for benzene degradation in mixed culture samples or at contaminated sites. To address this knowledge gap, DNA based stable isotope probing (SIP) was utilized to identify active benzene degraders in microcosms constructed with soil from three sources (a contaminated site and two agricultural sites). For this, replicate microcosms were amended with either labeled (¹³C) or unlabeled benzene and the extracted DNA samples were ultracentrifuged, fractioned and subject to terminal restriction fragment length polymorphism (TRFLP). The dominant benzene degraders (responsible for ¹³C uptake) were determined by comparing relative abundance of TRFLP phylotypes in heavy fractions of labeled benzene (¹³C) amended samples to the controls (from unlabeled benzene amended samples). Two phylotypes (a Polaromonas sp. and an Acidobacterium) were the major benzene degraders in the microcosms constructed from the contaminated site soil, whereas one phylotype incorporated the majority of the benzene-derived ¹³C in each of the agricultural soils (“candidate” phylum TM7 and an unclassified Sphingomonadaceae).     

Reductive Dechlorination of Tetrachloroethene Following Abiotic Versus Biotic Reduction of Hexavalent Chromium

A feasibility evaluation identified chemical reduction and biostimulation as a potential remedy for a plume containing hexavalent chromium (Cr(VI)) and tetrachloroethene (PCE) at an industrial site in southern California. The objectives of this laboratory study were to determine the stoichiometry of calcium polysulfide (CaS_x) reaction with Cr(VI) in the presence of sediment, the effect of CaS_x on the potential for in situ biological reductive dechlorination of PCE, and the potential to reduce Cr(VI) and PCE by addition of only an electron donor. Approximately 1 L of CaS_x solution (containing 50 g S^2-/L) was required per 1000 L of groundwater containing 45 mg/L of Cr(VI) (i.e., 1.8 mol S^2- per mol Cr(VI)). The sediment also exerted a sulfide demand (≥0.38 g S^{2 -} per kg sediment), but at a slower rate than the Cr(VI). In microcosms prepared with lactate, corn syrup, soybean oil, or methanol, but no CaS_x, the Cr(VI) was biologically reduced in the treatments with lactate and corn syrup, but much more slowly than with CaS_x. Even after 20 months of incubation, no significant reductive dechlorination of PCE occurred in any of the microcosms, including those in which the Cr(VI) was removed with CaS_x. Bioaugmentation was tested with the microcosms that received lactate and corn syrup (following 20 months of incubation), using an enrichment culture that actively dechlorinates trichloroethene. PCE dechlorination began within 1 month in the lactate-only treatment; in the corn syrup-amended treatment, PCE dechlorination occurred in only one of the three bottles. However, no PCE dechlorination occurred following bioaugmentation of the lactate and corn syrup microcosms that were initially treated with CaS_x, indicating that CaS_x (and/or its reaction products) exerted a negative impact on the chlororespiring microbes. This outcome highlights the need to evaluate sites on a case-by-case basis when in situ chemical treatment is applied prior to microbial reductive dechlorination.     

牛樟芝多糖对HepG2细胞酒精性氧化损伤的保护作用

研究了不同剂量(100、200和400μg/mL)的牛樟芝粗多糖(CP)和醇提物后的水提物(WEE)对酒精诱导的HepG2细胞氧化损伤的保护作用.研究结果表明:与模型组比较,各剂量组的CP和200、400μg/mL的WEE均能极显著提高HepG2细胞的细胞活力.100μg/mL的CP和WEE均能极显著降低细胞培养液的A...