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PubMed2001

Cl atom-initiated oxidation of three homologous methyl perfluoroalkyl ethers.

Chlorine atom-initiated photooxidations of three homologous methyl perfluoroalkyl ethers (HFEs), n-C(n)F(2n+1)OCH3 (n = 2, 3, and 5), in air in the absence of NOx were investigated with a long path FTIR/photochemical reaction system to elucidate the degradation mechanisms. The environmental removal processes of these three ethers in the troposphere were estimated. For oxidation of the three ethers, perfluoroalkyl formates (C(n)F(2n+1)OCHO; n = 2, 3 and 5) as relatively stable intermediates were produced at unity of the production ratio, which was independent of the perfluoroalkyl length. The rate constants for the reaction of Cl atoms with C2F5OCHO, C3F7OCHO, and C5F11OCHO were (1.2 +/- 0.5) x 10(-14), (1.2 +/- 0.5) x 10(-14), and (1.8 +/- 0.7) x 10(-14) cm3 molecule(-1) s(-1), respectively. The rate constants of the reaction of Cl with produced perfluoroalkyl formates were larger than these of perfluoroalkyl ethers. The formyl group of the perfluoroalkyl formates was finally converted to carbon dioxide. The -CF2- of the perfluoroalkyl groups for the three ethers was mainly converted to COF2 through the C-C cleavage; the conversion ratios from the carbons of the perfluoroalkyl group to COF2 were 48 +/- 10, 76 +/- 10, and 60 +/- 10% for C2F5OCH3, n-C3F7OCH3, and n-C5F11OCH3, respectively. Sixteen percent of the perfluoroalkyl group for n-C3F7OCH3 was converted to C2F5COF. Similarly, the perfluoroalkyl group of n-C5F11OCH3 was converted to C(n)F(2n+1)COF (n = 2, 3, and/or 4) with the yield of 15-30%, while for C2F5OCH3, the formation of CF3COF was not confirmed. As an oxidation product of the terminal CF3- group, 20, 22, and 16% of the CF3 group for C2F5OCH3, n-C3F7OCH3, and n-C5F11OCH3, respectively, were converted to CF3OOOCF3.

Biodegradation, Environmental↗

PubMed2005

Monitoring of the process of composting of kitchen waste in an institutional scale worm farm.

Vermicomposting provides an alternative method of managing waste that is ecofriendly and cost-effective. The Environmental Technology Centre (ETC) at Murdoch University and St. John of God Hospital (SJOG) signed a Memorandum of Understanding (MOU) to install a vermiculture system in SJOG to treat some of the organic waste generated by the on site kitchen facility. This is an effort made by SJOG to reduce the amount of organic waste sent to landfill each year and to treat the waste on site as part of a recycling/reuse program. The study is aimed at scientifically monitoring vermicomposting process and to understand the optimum management requirements to improve the operation of an institutional scale worm farm. In addition, an experiment was conducted to investigate the suitability of bedding materials: horse manure, cow manure, peat coir, and natural bedding (vermicast). The species of earthworms used in this experiment were Red (Lumbricus rubellus), Tiger (Eisenia fetida), and Blue (Lumbricus excavatus). The pH, temperature, worm population and quality of castings were tested in different beds. Results indicated that vermicast was the best bedding for vermicomposting, and there were no significant difference between the performances of the other three beds. However, it can be concluded that the bedding material of horse manure, cow manure, and peat coir were successfully established well within the experimental period of eight weeks, and cow manure with the lowest C:N ratio produced the best quality bedding. As using vermicast for the initial bedding creates a very high capital cost these organic substrates provide cost-effective alternative. Therefore they would be quite appropriate to initiate an institutional scale worm farm.

Animals↗

PubMed1999

Factors influencing expression of luxCDABE and nah genes in Pseudomonas putida RB1353(NAH7, pUTK9) in dynamic systems.

Bioluminescent reporter organisms have been successfully exploited as analytical tools for in situ determination of bioavailable levels of contaminants in static environmental samples. Continued characterization and development of such reporter systems is needed to extend the application of these bioreporters to in situ monitoring of degradation in dynamic environmental systems. In this study, the naphthalene-degrading, lux bioreporter bacterium Pseudomonas putida RB1353 was used to evaluate the relative influences of cell growth stage, cell density, substrate concentration, oxygen tension, and background carbon substrates on both the magnitude of the light response and the rate of salicylate disappearance. The effect of these variables on the lag time required to obtain maximum luminescence and degradation was also monitored. Strong correlations were observed between the first three factors and both the magnitude and induction time of luminescence and degradation rate. The maximum luminescence response to nonspecific background carbon substrates (soil extract broth or Luria broth) was 50% lower than that generated in response to 1 mg of sodium salicylate liter(-1). Oxygen tension was evaluated over the range of 0.5 to 40 mg liter(-1), with parallel inhibition to luminescence and degradation rate (20 mg of sodium salicylate liter(-1)) observed at 1.5 mg liter(-1) and below and no effect observed above 5 mg liter(-1). Oxygen tensions from 2 to 4 mg liter(-1) influenced the magnitude of luminescence but not the salicylate degradation rate. The results suggest that factors causing parallel shifts in the magnitude of both luminescence and degradation rate were influencing regulation of the nah operon promoters. For factors that cause nonparallel shifts, other regulatory mechanisms are explored. This study demonstrates that lux reporter bacteria can be used to monitor both substrate concentration and metabolic response in dynamic systems. However, each lux reporter system and application will require characterization and calibration.

Biodegradation, Environmental↗

PubMed2004

Effect of grasses on herbicide fate in the soil column: infiltration of runoff, movement, and degradation.

The objective of the present study was to evaluate if the presence of grass or the type of grass influences the environmental fate of herbicides within a soil column. Intact soil columns were planted with either smooth brome, big bluestem, tall fescue, switchgrass, or a mixture of prairie grasses or were left unvegetated. Artificial runoff containing atrazine, metolachlor, and pendimethalin was applied to the columns and allowed to infiltrate, and the resulting leachate was collected at the bottom of the soil column. This process was repeated on day 7 with herbicide-fortified runoff and on days 14 and 21 with water only. Following the leaching experiments, soil from the columns was fortified with either [14C]atrazine or [14C]metolachlor to measure pesticide degradation potential. The mean time necessary for infiltration of the artificial runoff decreased from 7.5 h for unvegetated to 3.4 h for grassed soil columns, and the type of grass did not have a significant effect. Neither the type of grass nor the presence of grass caused a significant change in the total amount of herbicide that leached through the columns. However, the presence of some grasses did decrease the amount of herbicide that leached in the final two events (i.e., additions not fortified with herbicide). Fescue was the least effective, reducing the amount of leached atrazine and metolachlor by 13% and 33% respectively, and mixed prairie grass was most effective, with reductions of 43% and 44%, respectively. In addition, atrazine and metolachlor degraded more rapidly in soil vegetated by some grasses. Mixed prairie grass had the greatest effect, increasing atrazine mineralization by 260% and formation of metolachlor-bound residue by 760%.

Acetamides↗

PubMedDate not supplied

Plant processes important for the transformation and degradation of explosives contaminants.

Environmental contamination by explosives is a worldwide problem. Of the 20 energetic compounds, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are the most powerful and commonly used. Nitroamines are toxic and considered as possible carcinogens. The toxicity and persistence of nitroamines requires that their fate in the environment be understood and that contaminated soil and groundwater be remediated. This study, written as a minireview, provides further insights for plant processes important for the transformation and degradation of explosives. Plants metabolize TNT and the distribution of the transformation products, conjugates, and bound residues appears to be consistent with the green liver model concept. Metabolism of TNT in plants occurs by reduction as well as by oxidation. Reduction probably plays an important role in the tolerance of plants towards TNT, and, therefore a high nitroreductase capacity may serve as a biochemical criterion for the selection of plant species to remediate TNT. Because the activities and the inducibilities of the oxidative enzymes are far lower than of nitroreductase, reducing processes may predominate. However, oxidation may initiate the route to conjugation and sequestration leading ultimately to detoxification of TNT, and, therefore, particularly the oxidative pathway deserves more study. It is possible that plants metabolize RDX also according to the green liver concept. In the case of plant metabolism of HMX, a conclusion regarding compliance with the green liver concept was not reached due to the limited number of available data.

Biodegradation, Environmental↗

PubMed2006

Anaerobic degradation of brominated flame retardants in sewage sludge.

Tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and decabromodiphenyl ether (DecaBDE) are high production volume chemicals used as flame retardants in plastics for products such as electronic equipment, insulation panels, and textiles. The environmental safety of brominated flame retardants, especially their persistence, bioaccumulation, and toxicity is a controversial topic. Here, we studied and compared the degradation of TBBPA, HBCD, and DecaBDE under anaerobic conditions in digested sewage sludge. The half-lives of TBBPA and a technical HBCD mixture were 0.59 and 0.66 d, respectively. The fact that (+/-)-alpha-HBCD exhibited an almost doubled half-life compared to (+/-)-beta-HBCD and (+/-)-gamma-HBCD is an important finding with respect to the discussion on the persistence of individual HBCD stereoisomers and the recent reports on strong relative enrichment of alpha-HBCD in biota. We found no statistically significant enantioselective degradation of alpha-, beta-, or gamma-HBCD. Half-lives of TBBPA and a technical HBCD mixture were not dependent on the presence of additional nutrients or primers. Concentrations of TBBPA and a technical HBCD mixture decreased also in sterile control samples, however, at a rate that was more than a factor of 50 smaller than in incubations under non-sterile conditions. Compared to TBBPA and a technical HBCD mixture, DecaBDE exhibited a much longer half-life of 7 x 10(2)d in the same system. Pseudo-first-order degradation rate constants decreased according to the following sequence: TBBPA congruent with(+/-)-gamma-HBCD congruent with(+/-)-beta-HBCD>(+/-)-alpha-HBCD>>DecaBDE. Preliminary investigations suggest that degradation of TBBPA, HBCD, and DecaBDE occurs in full-scale anaerobic digesters, as well.

Anaerobiosis↗

PubMedDate not supplied

Enrichment and isolation of endosulfan-degrading microorganisms.

Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,3,4-benzo-dioxathiepin-3-oxide) is a cyclodiene organochlorine currently used as an insecticide all over the world and its residues are posing a serious environmental threat. This study reports the isolation and identification of enriched microorganisms, capable of degrading endosulfan. Enrichment was achieved by using the insecticide as either the sole source of carbon or sulfur in parallel studies. Two strains each of fungi (F1 and F4) and bacteria (BF2 and B4) were selected using endosulfan as a sole carbon source. A Pandoraea species (Lin-3) previously isolated in our laboratory using lindane (gamma-HCH) as a carbon source was also screened for endosulfan degradation. F1 and F4 (Fusarium ventricosum) degraded alpha-endosulfan by as much as 82.2 and 91.1% and beta-endosulfan by 78.5 and 89.9%, respectively, within 15 d of incubation. Bacterial strains B4 and Lin-3 degraded alpha-endosulfan up to 79.6 and 81.8% and beta-endosulfan up to 83.9 and 86.8%, respectively, in 15 d. Among the bacterial strains isolated by providing endosulfan as a sulfur source, B4s and F4t degraded alpha-endosulfan by as much as 70.4 and 68.5% and beta-endosulfan by 70.4 and 70.8%, respectively, after 15 d. Degradation of the insecticide occurred concomitant with bacterial growth reaching an optical density (OD600) of 0.366 and 0.322 for B4 and Lin-3, respectively. High OD600 was also noted with the other bacterial strains utilizing endosulfan as a sulfur source. Fungal and bacterial strains significantly decreased the pH of the nutrient culture media while growing on endosulfan. The results of this study suggest that these novel strains are a valuable source of potent endosulfan-degrading enzymes for use in enzymatic bioremediation.

Biodegradation, Environmental↗

PubMedDate not supplied

Characterization of lead removal from contaminated soils by nontoxic soil-washing agents.

Few effective strategies exist for remediating and restoring metal-contaminated soils. We have evaluated the potential of two environmentally compatible, nondestructive, biological soil-washing agents for remediating aged, lead-contaminated soils. Two contaminated soils were washed with 10 mM rhamnolipid biosurfactant and 5.3% carboxymethyl-beta-cyclodextrin (CMCD). The metal removal efficiency of these agents was compared with 10 mM diethylenetriamine pentaacetic acid (DTPA) and 10 mM KNO3. Lead removal rates by both soil-washing agents exceeded the removal by KNO3, but were an order of magnitude less than removal by the synthetic chelator, DTPA. Analysis of soil extractions revealed that the Pb in the first soil (3780 mg kg(-1)) was primarily associated with the soluble, exchangeable, oxide, and residual fractions while the Pb in the second soil (23 900 mg kg(-1)) was found in the soluble, exchangeable, carbonate, and residual fractions. After 10 consecutive washes, rhamnolipid had removed 14.2 and 15.3% of the Pb from the first and second soils, respectively, and CMCD had removed 5 and 13.4% from the same two soils. The Pb removal rate by both agents either increased or was consistent throughout the 10 extractions, indicating a potential for continued removal with extended washing. Significant levels of Cu and Zn in both soils did not prevent Pb removal by either agent. Interestingly, the effectiveness of each agent varied as a function of Pb speciation in the soil. Rhamnolipid was more effective than CMCD in removing Pb bound to amorphous iron oxides, while both agents demonstrated similar potential for removing soluble, exchangeable, and carbonate-bound Pb. Neither agent demonstrated potential for the complete remediation of metal-contaminated soils.

Biodegradation, Environmental↗

PubMed2001

Effect of temperature, organic amendment rate and moisture content on the degradation of 1,3-dichloropropene in soil.

1,3-Dichloropropene (1,3-D), which consists of two isomers, (Z)- and (E)-1,3-D, is considered to be a viable alternative to methyl bromide, but atmospheric emission of 1,3-D is often associated with deterioration of air quality. To minimize environmental impacts of 1,3-D, emission control strategies are in need of investigation. One approach to reduce 1,3-D emissions is to accelerate its degradation by incorporating organic amendments into the soil surface. In this study, we investigated the ability of four organic amendments to enhance the rate of degradation of (Z)- and (E)-1,3-D in a sandy loam soil. Degradation of (Z)- and (E)-1,3-D was well described by first-order kinetics, and rates of degradation for the two isomers were similar. Composted steer manure (SM) was the most reactive of the organic amendments tested. The half-life of both the (Z)- and (E)-isomers in unamended soil at 20 degrees C was 6.3 days; those in 5% SM-amended soil were 1.8 and 1.9 days, respectively. At 40 degrees C, the half-life of both isomers in 5% SM-amended soil was 0.5 day. Activation energy values for amended soil at 2, 5 and 10% SM were 56.5, 53.4 and 64.5 kJ mol-1, respectively. At 20 degrees C, the contribution of degradation from biological mechanisms was largest in soil amended with SM, but chemical mechanisms still accounted for more than 58% of the (Z)- and (E)-1,3-D degradation. The effect of temperature and amendment rate upon degradation should be considered when describing the fate and transport of 1,3-D isomers in soil. Use of organic soil amendments appears to be a promising method to enhance fumigant degradation and reduce volatile emissions.

Air Pollutants↗

PubMed2005

Cyanide detoxification by recombinant bacterial rhodanese.

Cyanide is a major environmental pollutant of the chemical and metallurgical industries. Although extremely toxic, cyanide can enzymatically be converted to the less toxic thiocyanate by rhodaneses (thiosulfate:cyanide sulfurtransferases, EC 2.8.1.1). We engineered a genetic system to express high levels of recombinant Pseudomonas aeruginosa rhodanese (r-RhdA) in Escherichia coli, and used this organism to test the role of r-RhdA in cyanide detoxification. Inducible expression of the rhdA gene under the control of the hybrid T7-lacO promoter yielded active r-RhdA over a 4-h period, though r-RhdA-expressing E. coli showed decreased viability starting from 1 h post-induction. At this time, Western blot analysis and enzymatic assay showed r-RhdA partition between the cytoplasm (95%) and the periplasm (5%). The accessibility of thiosulfate to r-RhdA was a limiting step for the sulfur transfer reaction in the cellular system, but cyanide conversion to thiocyanate could be increased upon permeabilization of the bacterial membrane. Specific r-RhdA activity was higher in the whole-cell assay than in the in vitro assay with pure enzyme (2154 vs. 816 micromol min-1 mg-1 r-RhdA, respectively), likely reflecting enzyme stability. The r-RhdA-dependent cyanide detoxification resulted in increased resistance of r-RhdA overexpressing E. coli to 5 mM cyanide. Bacterial survival was paralleled by release of thiocyanate into the medium. Our results indicate that cyanide detoxification by engineered E. coli cells is feasible under laboratory conditions, and suggest that microbial rhodaneses may contribute to cyanide transformation in natural environments.

Biodegradation, Environmental↗

PubMed2006

Nutrient regulation of organic matter decomposition in a tropical rain forest.

Terrestrial biosphere-atmosphere CO2 exchange is dominated by tropical forests, so understanding how nutrient availability affects carbon (C) decomposition in these ecosystems is central to predicting the global C cycle's response to environmental change. In tropical rain forests, phosphorus (P) limitation of primary production and decomposition is believed to be widespread, but direct evidence is rare. We assessed the effects of nitrogen (N) and P fertilization on litter-layer organic matter decomposition in two neighboring tropical rain forests in southwest Costa Rica that are similar in most ways, but that differ in soil P availability. The sites contain 100-200 tree species per hectare and between species foliar nutrient content is variable. To control for this heterogeneity, we decomposed leaves collected from a widespread neotropical species, Brosimum utile. Mass loss during decomposition was rapid in both forests, with B. utile leaves losing >80% of their initial mass in <300 days. High organic matter solubility throughout decomposition combined with high rainfall support a model of litter-layer decomposition in these rain forests in which rapid mass loss in the litter layer is dominated by leaching of dissolved organic matter (DOM) rather than direct CO2 mineralization. While P fertilization did not significantly affect mass loss in the litter layer, it did stimulate P immobilization in decomposing material, leading to increased P content and a lower C:P ratio in soluble DOM. In turn, increased P content of leached DOM stimulated significant increases in microbial mineralization of DOM in P-fertilized soil. These results show that, while nutrients may not affect mass loss during decomposition in nutrient-poor, wet ecosystems, they may ultimately regulate CO2 losses (and hence C storage) by limiting microbial mineralization of DOM leached from the litter layer to soil.

Biodegradation, Environmental↗

PubMed2002

The genotoxicity of priority polycyclic aromatic hydrocarbons in complex mixtures.

Risk assessment of complex environmental samples suffers from difficulty in identifying toxic components, inadequacy of available toxicity data, and a paucity of knowledge about the behavior of geno(toxic) substances in complex mixtures. Lack of information about the behavior of toxic substances in complex mixtures is often avoided by assuming that the toxicity of a mixture is simply the sum of the expected effects from each mixture component, i.e. no synergistic or antagonistic interactions. Although this assumption is supported by research investigating non-genotoxic end-points, the literature describing the behavior of genotoxic substances in complex mixtures is sparse and, occasionally, contradictory. In this study, the results of polycyclic aromatic hydrocarbon (PAH) analyses on freshwater bivalves were used to prepare realistic mixtures containing up to 16 PAHs. The SOS genotoxicity of the mixtures and each component were then assessed in an effort to evaluate the additivity of PAH genotoxicity. At nominal PAH concentrations above 1 microg/ml, observed genotoxic responses were far lower than those predicted under the assumption of additivity. At nominal concentrations below 0.75 microg/ml, differences are smaller and occasionally negligible, indicating that the genotoxicity of unsubstituted homocyclic PAHs is additive or slightly less than additive. Other researchers who have investigated the mutagenicity, carcinogenicity, and DNA binding activity of mixtures containing unsubstituted homocyclic PAHs have also reported additive effects. Therefore, the mutagenic risk posed by simple, well-characterized mixtures of priority PAHs can reasonably be estimated as the sum of the risks posed by the mixture components. Current data indicate that less-than-additive effects likely result from saturation of metabolic pathways needed to activate mutagenic PAHs.

Animals↗

PubMed2004

Streptomycin as a selective agent to facilitate recovery and isolation of introduced and indigenous Sphingomonas from environmental samples.

Sphingomonas is an organism of major interest for the degradation of organic contaminants in soils and other environments. A medium based on the aminoglycoside antibiotic streptomycin (Sm) was developed, which, together with the yellow pigmentation of Sphingomonas, facilitated the detection, recovery and quantification of culturable Sphingomonas from soils. All 29 previously described bacterial strains belonging to 17 different Sphingomonas species were able to grow on mineral media containing 200 microg ml(-1) streptomycin, showing that the capacity to resist high concentrations of Sm is a common characteristic within Sphingomonas. Incorporation of Sm into the mineral medium led to a significant reduction in the background microbial population and a concomitant 100 times more sensitive detection of Sphingomonas inoculated in non-sterile soil matrices. The Sm-containing medium was used to examine a variety of hydrocarbon-contaminated soils for the presence and biodiversity of Sphingomonas. Incorporation of Sm in the medium led to a significant increase in the number of yellow-pigmented colonies. Comparison of contaminated and non-contaminated soils derived from the same site revealed colonization by culturable yellow-pigmented Sm-resistant bacteria of the polluted location solely. Both yellow and non-yellow-pigmented colonies were purified from plates containing glucose and Sm, and BOX-polymerase chain reaction (PCR) was used to sort out clonally related strains. Representative strains from the major BOX-PCR clusters were identified using FAME and partial 16S rRNA gene sequencing. Forty-eight of 58 Sm-resistant isolates were identified as Sphingomonas sp. Streptomycin-resistant Sphingomonas isolates generated BOX-PCR diversity patterns that were site dependent and represented different species mainly belonging to Sphingomonas subgroups containing species formerly designated as Sphingopyxis and Sphingobium. The ability to degrade phenanthrene was only found in a minority of the Sphingomonas isolates, which all originated from soils containing high phenanthrene concentrations.

Anti-Bacterial Agents↗

PubMed2006

Multi tracer test for the implementation of enhanced in-situ bioremediation at a BTEX-contaminated megasite.

At the Centre for Environmental Research Leipzig-Halle (UFZ) research site in Zeitz, Germany, benzene contaminates the lower of two aquifers with concentrations of up to 20 mg/l. Since the benzene plume has a minimum length of approximately 1 km, enhanced natural attenuation measures are being considered as a remediation strategy. This study describes the performance and evaluation of a multi-species reactive tracer test using the tracers fluorescein and bromide as conservative tracers and toluene as reactive tracer. Sampling was performed over a period of six months using a detailed network of multilevel sampling wells. Toluene was only slightly retarded in comparison to bromide, whereas fluorescein was retarded considerably stronger. Therefore, it was not possible to use fluorescein as an in situ tracer for the determination of groundwater velocities. The ionic nature of fluorescein is assumed to be the major reason for its retardation. The results show that the infiltration conditions were suitable to produce a wide spreading of the tracer front along the full thickness of the aquifer. Thus, a large aquifer volume can be treated in future enhanced bioremediation measures. The total quantity of infiltrated toluene (24 l) was degraded under sulfate-reducing conditions over a flow path of 50 m. Benzylsuccinate was identified as a metabolite of toluene degradation under sulfate-reducing conditions at this site. The modelling results show that toluene degradation was described more accurately using Monod kinetics than first-order kinetics. Since toluene was only slightly retarded in comparison to bromide, sorption and desorption processes were considered to be negligible.

Biodegradation, Environmental↗

PubMed2005

Anaerobic degradation of decabromodiphenyl ether.

The environmental safety of decabromodiphenyl ether (BDE-209), a widely used flame retardant, has been the topic of controversial discussions during the past several years. Degradation of BDE-209 into lower brominated diphenyl ether congeners, exhibiting a higher bioaccumulation potential, has been a critical issue. Here, we report on the degradation of BDE-209 and the formation of octa- and nonabromodiphenyl ether congeners under anaerobic conditions. Sewage sludge collected from a mesophilic digester was used as the inoculum and incubated up to 238 days with and without a set of five primers. Following Soxhlet extraction and a liquid chromatography cleanup procedure, parent compounds and debromination products were analyzed by GC/HRMS. In experiments with primers, concentrations of BDE-209 decreased by 30% within 238 days. This corresponds to a pseudo-first-order degradation rate constant of 1 x 10(-3) d(-1). Without primers, the degradation rate constant was 50% lower. Formation of two nonabromodiphenyl ether and six octabromodiphenyl ether congeners proved that BDE-209 underwent reductive debromination in these experiments. Debromination occurred at the para and the meta positions, whereas debromination at the ortho position was not statistically significant. All three nonabromodiphenyl ether congeners (BDE-206, BDE-207, and BDE-208) were found to undergo reductive debromination as well. No significant change of the BDE-209 concentration and no formation of lower brominated congeners was observed in sterile control experiments. To our knowledge, this is the first report demonstrating microbially mediated reductive debromination of BDE-209 under anaerobic conditions.

Animals↗

PubMed2001

In vitro study of the biochemical origin and production limits of odorous compounds in cattle feedlots.

Livestock odors are closely correlated to airborne concentrations of volatile organic compounds (VOC), which are a complex mixture of carbon-, sulfur-, and nitrogen-containing compounds produced primarily during the incomplete anaerobic fermentation of animal manure by microorganisms. Volatile fatty acids, alcohols, and aromatic ring compounds comprise a substantial fraction of VOC, yet very little is known about their biochemical origin and environmental factors controlling their production. The anaerobic production of fermentation products and consumption of substrates (CP, starch, and nonstarch carbohydrate) were analyzed in slurries of fresh (< 24 h) and aged (> 1 d) cattle manure over several weeks. Ethanol, acetate, propionate, butyrate, lactate, and H2 were the major products of fermentation. Aged cattle manure produced twice the concentration of VFA during incubation produced by the fresh manure (P < 0.001). Aromatic compounds (phenols, indoles, and benzoates) remained unchanged in both manures. Production of VFA from fresh manure was inhibited when the pH fell below 4.5. It is likely that the presence of calcareous soil, which has a high buffering capacity, and lactate-consuming microorganisms minimized acidification in the aged manure slurries. Low starch content limited VFA production in the aged manure. Starch was the likely biochemical source for fermentation products in both manures based on the strong negative correlations between fermentation product and starch content (r = -0.944 and -0.773) and ratio of fermentation products produced to starch consumed (r = 0.64 and 0.72) for fresh and aged manure, respectively. Nonstarch carbohydrate served an indeterminate role in the production of fermentation products. Nonstarch carbohydrate decreased by 4.7 and 23.4 g/L in the fresh and aged manure, respectively, whereas the starch content decreased by 18.6 and 22.4 g/L in the fresh and aged manure, respectively. The concentration of CP did not change, which suggests a balance between protein consumption and new bacterial biomass production. We conclude that the types of substrates in cattle manure and the feedlot soils where they are deposited are significant factors in the production of odors.

Animals↗

PubMed2003

Comparing the dehalogenase gene pool in cultivated alpha-halocarboxylic acid-degrading bacteria with the environmental metagene pool.

Culture-dependent and culture-independent approaches were used to determine the relationship between the dehalogenase gene pool in bacteria enriched and isolated on 2,2-dichloropropionic acid (22DCPA) and the environmental metagene pool (the collective gene pool of both the culturable and uncultured microbes) from which they were isolated. The dehalogenases in the pure-cultures isolates, which were able to degrade 22DCPA, were similar to previously described group I and II dehalogenases. Significantly, the majority of the dehalogenases isolated from activated sludge by degenerate PCR with primers specific for alpha-halocarboxylic acid dehalogenases were not closely related to the dehalogenases in any isolate. Furthermore, the dehalogenases found in the pure cultures predominated in the enrichments but were a minor component of the community used to inoculate the batch cultures. Phylogenetic analysis of the dehalogenase sequences isolated by degenerate PCR showed that the diversity of the group II deh gene was greater than that of the group I deh gene. Direct plating of the activated sludge onto minimal media supplemented with 22DCPA resulted in biomass and DNA from which dehalogenases were amplified. Analysis of the sequences revealed that they were much more closely related to the sequences found in the community used to start the enrichments. However, no pure cultures were obtained with this isolation method, and thus no pure cultures were available for identification. In this study we examined the link between genes found in pure cultures with the metagene pool from which they were isolated. The results show that there is a large bias introduced by culturing, not just in the bacteria isolated but also the degradative genes that they contain. Moreover, our findings serve as a caveat for studies involving the culturing of pure cultures of bacteria and conclusions which are drawn from analysis of these organisms.

Bacteria↗

PubMed1987

A record of polycyclic aromatic hydrocarbon (PAH) pollution obtained from accreting sediments of the Tamar Estuary, U.K.: evidence for non-equilibrium behaviour of PAH.

Concentrations of polycyclic aromatic hydrocarbons (PAH) were quantified throughout a 210Po-dated inter-tidal sediment core from the Tamar Estuary, U.K. in order to reconstruct the input history and investigate environmental reactivity of PAH in sediments. The profile recorded is similar to those reported in other aquatic sedimentary studies, with an approximately exponential increase in the concentrations of individual PAH from less than 30 ng (g dry sediment)-1 prior to 1940 to between 100 and 1000 ng (g dry sediment)-1 in contemporary surface sediments. This corresponds to an increased input of total PAH from 0.23 to 21 mg m-2 year-1. The PAH composition is dominated by parent compounds rather than alkylated homologues and is characteristic of pyrogenic sources correlating with increased motor vehicle activity and road runoff into the Tamar. There is a remarkable compositional uniformity of PAH throughout the polluted sediment core, indicating that the biogeochemical transformation and exchange processes (sorption/leaching; microbial breakdown; photo-degradation; etc.) which are known to govern the fate of experimentally-added or petroleum-derived PAH, and which exhibit compound discrimination, appear not to affect PAH in the sediments. Using a linear free energy sediment-water exchange model to simulate the repartitioning and exchange of individual PAH between the surface-mixed layer of sediment and water, we demonstrate that the current PAH concentrations in sediments are between 2 and 5 orders of magnitude greater than those expected from equilibrium partitioning with observed water concentrations. This implies that the PAH input to the sediments has been compositionally uniform and that the PAH are chemically inert. Sorptive exchange with the aqueous phase and hence the potential bioavailability of PAH appear restricted by the existence of occluded and other micro-morphologically inert forms of particle-bound PAH.

Biodegradation, Environmental↗