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At least 919 records · Page 51Linked to original sources

PubMed2001

Fate of atmospherically deposited polycyclic aromatic hydrocarbons (PAHs) in Chesapeake Bay.

Factors controlling polycyclic aromatic hydrocarbon (PAH) distributions in southern Chesapeake Bay surface sediments were investigated with samples collected seasonally from five sites. Principal components analysis (PCA) suggests unique sources (combustion vs petroleum) and partitioning differences (volatile vs particle reactive) among PAHs, but a common mode of entry for these contaminants to Chesapeake Bay sediments. The fractional concentrations of all PAHs in Bay sediments, with the exception of perylene, were positively correlated with their atmospheric dry deposition fluxes (Fdry) to the Bay indicating that atmospheric deposition of aerosol-bound PAHs to the watershed controls their influx to Bay sediments. Overall, PAH concentrations in Chesapeake Bay sediments were well explained by a multiple-regression model (r2 = 0.88, p = 0.0001) with Fdry and sediment total organic carbon (TOC) content explaining most of the variance (57% and 43%, respectively). However, for many PAHs gas exchange across the air-water interface is of similar or greater magnitude even when Fdry is scaled to the watershed surface area. The fate of PAHs input to the Bay from gas deposition was determined to be uptake and metabolism within the aquatic food web rather than deposition to sediments.

Aerosols↗

PubMed2003

Reductive dehalogenation of halomethanes in iron- and sulfate-reducing sediments. 1. Reactivity pattern analysis.

The incorporation of reductive transformations into environmental fate models requires the characterization of natural reductants in sediments and aquifer materials. For this purpose, reactivity patterns (range and relative order of reactivity) for a series of 14 halogenated methanes were measured in iron- and sulfate-reducing sediments and two representative model systems: adsorbed Fe(II)/goethite [Fe(II)ads/alpha-FeOOH] and iron sulfide (FeS). Both Fe(II)ads and FeS are naturally occurring reductants. The strong similarity in reactivity patterns between the iron- and sulfate-reducing sediments suggests that the two share a common reductant despite their different chemical compositions (i.e., the sulfate-reducing sediment contained FeS). An orthogonal regression analysis of the halomethane transformation rate data in the sediment and model systems supports the assumption that a common mechanism for halomethane transformation exists between the sediments and the Fe(II)ads/alpha-FeOOH system and further corroborates the conclusion that Fe(II) adsorbed to Fe(III)-containing minerals is the dominant reductant in both sediment systems. Weak (0.5 N) and strong (6.0 N) acid extraction of the sediments indicated that solid-phase Fe(II) was 67% higher in the sulfate-reducing sediment than in the iron-reducing sediment, which is consistent with the observations that the halomethanes were transformed a factor of 3 times faster in the sulfate-reducing sediment and that Fe(II) was the dominant reductant.

Adsorption↗

PubMed2003

Bioaccumulation and toxic potencies of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in tidal flat and coastal ecosystems of the Ariake Sea, Japan.

Sediment and marine biota comprising several species of tidal flat and coastal organisms were analyzed for polychlorinated biphenyls (PCBs) including non- and mono-ortho coplanar congeners and polycyclic aromatic hydrocarbons (PAHs) to examine bioaccumulation profiles and toxic potencies of these contaminants. Concentrations of PCBs in tidal flat organisms ranged from 3.6 ng/g (wet wt) in clams to 68 ng/g (wet wt) in omnivore tidal flatfishes, a discernible trend reflecting concentrations and trophic levels. In contrast, PAHs concentrations were the highest in lower trophic organisms, such as crabs and lugworms from tidal flat, whereas those in coastal fishes, squid, and finless porpoises were less than detection limit. Greater bioaccumulation of PAHs was found in lugworms and crabs, which might be due to their direct ingestion of sediment particulates absorbed with PAHs. TCDD toxic equivalents (TEQs) were calculated for PCBs and PAHs in sediments and biota. PCBs accounted for a greater proportion of total TEQs (sum(TEQs): sum of TEQ(PCB) and TEQ(PAH)) in coastal and tidal flatfishes (>95%), while PAHs occupied a considerable portion of sum(TEQs) in sediment (>97%). Interestingly, TEQ(PAH) accounted for 37% and 81% of the sum(TEQs) in crabs and clams, respectively. Benzo[b]fluoranthene was the dominant contributor to TEQ(PAH) in both the species. Considering these observations, the environmental risks of PAHs may not be ignored in benthic tidal flat organisms due to their greater bioaccumulation through sediments.

Animals↗

PubMed2003

Dioxins in aquatic sediment and soil in the Kanto region of Japan: major sources and their contributions.

Major sources of dioxins (tetra- to octa-chlorinated dibenzo-p-dioxins and dibenzofurans) were quantitatively identified, and the contributions of each source were estimated in aquatic surface sediment and soil in the Kanto region of Japan, where a major part of the municipal, industrial, and agricultural activities in Japan take place. Detailed chromatographic peak-specific data corresponding to all dioxin compounds were used throughout the analysis to achieve source specificity. Four major sources were identified by using principal component analysis. Three of them were combustion processes, impurities in pentachlorophenol, and impurities in the diphenyl ether herbicide CNP. One, characterized by polychlorinated dibenzo-p-dioxins with 1,2,6,9-chlorine substitution, remained unattributed to any known source or transformation process. The composition of the unattributed source resembled those reported in sediment samples free from anthropogenic impacts. Contributions from the four major sources were estimated by using a mass balance receptor model, and the source contributions to each homologue varied among samples. Tokyo Bay sediment was characterized by the highest relative contribution from pentachlorophenol impurities in the region. The unattributed source contribution was most prominent in the Lake Kasumigaura sediment. The results indicated considerable contributions in aquatic surface sediment in the studied region from dioxin impurities in herbicides used in the past.

Agriculture↗

PubMed2003

Reductive dechlorination of polychlorinated biphenyls: threshold concentration and dechlorination kinetics of individual congeners in Aroclor 1248.

Reductive dechlorination of individual PCB congeners in Aroclor 1248 was investigated using sediment microorganisms from the St. Lawrence River (NY). No dechlorination was observed at Aroclor concentrations below 40 ppm [137 nmol (g of sediment)(-1)]. Above this threshold, congeners could be divided into three categories: group A, congeners that dechlorinated above 40 ppm; group B, congeners that dechlorinated only at high concentrations above 60 ppm [206 nmol (g of sediment)(-1)]; and group C, lower chlorinated congeners that increased in concentration. The dechlorination rate of congeners in groups A and B was a linear function of their initial sediment concentration. For group A congeners, the concentration intercepts of this linear function were the same as their concentrations in the Aroclor at the threshold concentration, and these therefore represented the threshold values. However, the intercepts of group B congeners were significantly higher than their levels at the threshold Aroclor concentration and were equivalent to their concentrations in Aroclor 1248 at about 75 ppm [258 nmol (g of sediment)(-1)]. The final concentrations of group A and group B congeners at the end of dechlorination were the same, regardless of their initial concentrations. These final concentrations were significantly lower than their threshold values. The accumulation rate of group C congeners was a linear function of their initial concentrations, and the total accumulation was greater at higher Aroclor concentrations in sediments.

Aroclors↗

PubMed2004

Contaminant trends in reservoir sediment cores as records of influent stream quality.

When reconstructing water-quality histories from lake and reservoir cores, it is sometimes assumed that the chemical signatures in the cores reflect historical water quality in the influent streams. To investigate this assumption, concentrations of metals, PAHs, and organochlorine compounds in sediment cores were compared to those associated with an influent-stream suspended sediment for three reservoirs in Fort Worth, TX, and two reservoirs in Boston, MA, U.S.A., and interpreted in light of land-use and regulation histories. In evaluating relations between suspended sediments and cores, three levels of preservation were indicated: (1) influent concentrations and historical trends are preserved in cores (metals at all sites; some organic contaminants at some sites); (2) some loss occurs during transport and initial deposition but relative historical trends are preserved in cores (some organic contaminants at some sites); and (3) neither stream concentrations nor relative historical trends are preserved (dieldrin and p,p'-DDT). The degree of preservation of influent concentration histories varied between lakes, particularly for PAHs. The results support the use of sediment cores to infer streamwater-quality histories for many contaminants but indicate that reservoir-bottom sediment samples might underestimate concentrations of organic contaminants in some streams.

Environmental Monitoring↗

PubMed2001

Distribution of heavy metals in surface sediments from an Antarctic marine ecosystem.

The concentrations of lead, cadmium, copper, chromium, iron, manganese and zinc in surface sediments collected from Potter Cove, in the 25 de Mayo Island (King George Island), Antarctica, and its drainage basin, were measured by atomic absorption spectroscopy. The obtained results were use to determine the areal and vertical distribution of the metals of in the Cove and potential sources of these metals to this environment. The geochemical data suggest that most of the metals found in Potter Cove constitute a redistribution of autochthonous materials within the ecosystem. Therefore, the metal concentrations can be considered to be present at natural background levels in surface sediments.

Antarctic Regions↗

PubMed2000

Monitoring the quality of the marine environment.

As part of the monitoring program from Instituto Hidrográfico, since 1981 sediment and water samples have been collected from four different estuarine areas located along the continental coast of Portugal. The concentrations of different parameters were measured in the water and sediment samples. After normalization, the concentrations of chromium, mercury, lead and zinc in the sediments from the different areas were compared.

Environmental Monitoring↗

PubMed2004

Polycyclic aromatic hydrocarbons in sediments and mussels of Corral Bay, south central Chile.

PAHs were measured in sediments and mussels (Mytilus chilensis) from Carboneros and Puerto Claro, located in Corral Bay, Valdivia. According to the ratio of phenanthrene/anthracene and fluoranthene/pyrene concentrations, these sites are medium polluted with PAHs originating mainly from pyrolytic sources. Fluoranthene was the major component measured in mussels (3.1-390 ng g(-1) dry weight) and sediments (6.9-74.1 ng g(-1) dry weight). In general, mussels were mainly exposed to the dissolved fraction of the lower molecular weight PAHs (tri- and tetra-aromatics) while the higher molecular ring systems (penta- and hexa-aromatics) were more bioavailable to sediments. Mussel PAHs content was relatively constant, with the exception of the 1999 summer season (March), when higher concentration values were found in both sites; however, PAHs residues in sediments showed a temporal variation.

Animals↗

PubMed2001

Extraction and characterization of organic matter from surface waters (reservoir of Keddara in Algeria).

The combined XAD-8 and XAD-4 resin procedure for isolating dissolved organic solutes from Keddara reservoir in Algeria was found to isolate 65% of total organic carbon (TOC). Of the 45% of solute adsorbed onto XAD-8 resin, 34% was in the form of fulvic acids, and 11% humic acids. Approximately 19% of the hydrophilic solutes were adsorbed onto XAD-4 resin. Characterization experiments have shown that the three isolated fractions have a low apparent molecular weight investigated by ultrafiltration and fluorescence and low aromaticity as shown by the results of UV-absorbance, the formation potential of total organic halogens (reactivity with chlorine) and the polyhydroxyaromatic (PHA) determined by pyrolysis gas chromatography/mass spectrometry (GC/MS) which show that the isolated fractions are aliphatic as well as aromatic. The low molecular weight and the low aromaticity compared with literature data are due to coagulation and sedimentation of NOM with high molecular weight, which occur naturally in the reservoir. The Keddara reservoir, with low hydraulic loading area and long detention times receiving water with low NOM and high in hardness can be expected to be very effective coagulation and sedimentation basins.

Benzopyrans↗

PubMed2006

The carbon cycle and associated redox processes through time.

Earth's biogeochemical cycle of carbon delivers both limestones and organic materials to the crust. In numerous, biologically catalysed redox reactions, hydrogen, sulphur, iron, and oxygen serve prominently as electron donors and acceptors. The progress of these reactions can be reconstructed from records of variations in the abundance of 13C in sedimentary carbonate minerals and organic materials. Because the crust is always receiving new CO2 from the mantle and a portion of it is being reduced by photoautotrophs, the carbon cycle has continuously released oxidizing power. Most of it is represented by Fe3+ that has accumulated in the crust or been returned to the mantle via subduction. Less than 3% of the estimated, integrated production of oxidizing power since 3.8 Gyr ago is represented by O2 in the atmosphere and dissolved in seawater. The balance is represented by sulphate. The accumulation of oxidizing power can be estimated from budgets summarizing inputs of mantle carbon and rates of organic-carbon burial, but levels of O2 are only weakly and indirectly coupled to those phenomena and thus to carbon-isotopic records. Elevated abundances of 13C in carbonate minerals ca 2.3 Gyr old, in particular, are here interpreted as indicating the importance of methanogenic bacteria in sediments rather than increased burial of organic carbon.

Atmosphere↗

PubMed2006

Deinococcus radiodurans engineered for complete toluene degradation facilitates Cr(VI) reduction.

Toluene and other fuel hydrocarbons are commonly found in association with radionuclides at numerous US Department of Energy sites, frequently occurring together with Cr(VI) and other heavy metals. In this study, the extremely radiation-resistant bacterium Deinococcus radiodurans, which naturally reduces Cr(VI) to the less mobile and less toxic Cr(III), was engineered for complete toluene degradation by cloned expression of tod and xyl genes of Pseudomonas putida. The recombinant Tod/Xyl strain showed incorporation of carbon from 14C-labelled toluene into cellular macromolecules and carbon dioxide, in the absence or presence of chronic ionizing radiation. The engineered bacteria were able to oxidize toluene under both minimal and complex nutrient conditions, and recombinant cells reduced Cr(VI) in sediment microcosms. As such, the Tod/Xyl strain could provide a model for examining the reduction of metals coupled to organic contaminant oxidation in aerobic radionuclide-contaminated sediments.

Chromium↗

PubMed2002

Rapid determination of 226Ra and uranium isotopes in solid samples by fusion with lithium metaborate and alpha spectrometry.

A simple and rapid method has been developed to determine 226Ra in rocks, soils, and sediments. Samples are decomposed by fusion with lithium metaborate and the melt is dissolved in a solution containing sulfates and citric acid. During the dissolution, a fine suspension of mixed barium and radium sulfates is formed. The microcrystals are collected on a membrane filter (pore size 0.1 microm) and analysed in an alpha spectrometer. Application of a 133Ba tracer enables us to assess the loss of the analyte, which only rarely exceeds 10%. All analytical operations, beginning from sample decomposition to source preparation for alpha spectrometry, can be accomplished within 1 or 2 h. With uranium determination, the filtrate is spiked with a 232U tracer and passed through a column loaded with a Dowex AG (1 x 4) anion-exchange resin in the sulfate form. Interfering elements are eluted with dilute sulfuric acid followed by concentrated hydrochloric acid. Uranium is eluted with water, electrodeposited on silver discs, and analysed in the alpha spectrometer. The method was tested on reference soil and sediment materials and was found to be accurate within the estimated uncertainties.

Borates↗

PubMed2006

Quantification of mcrA by quantitative fluorescent PCR in sediments from methane seep of the Nankai Trough.

A quantitative fluorogenic PCR method for group-specific methyl coenzyme M reductase subunit A genes (mcrA) from methanotrophic archaea was established and applied to the characterization of microbial communities in anoxic methane seep sediments at the accretionary prism of the Nankai Trough. All of the previously identified subgroups of anaerobic methanotroph (ANME) mcrA genes were detected in the cores up to 25 cm below the seafloor, but distributional patterns of mcrA genes were found to differ according to depth. These findings suggest a distinct distribution of phylogenetically and physiologically diverse methanotrophic archaea that mediate methane oxidation in the anoxic sediments. This quantification method will contribute to future investigations of methanotrophic microbial ecosystems in anoxic marine sediments.

Anaerobiosis↗

PubMed2000

Nonbiological fractionation of iron isotopes.

Laboratory experiments demonstrate that iron isotopes can be chemically fractionated in the absence of biology. Isotopic variations comparable to those seen during microbially mediated reduction of ferrihydrite are observed. Fractionation may occur in aqueous solution during equilibration between inorganic iron complexes. These findings provide insight into the mechanisms of iron isotope fractionation and suggest that nonbiological processes may contribute to iron isotope variations observed in sediments.

Chemical Fractionation↗

PubMed1999

Anaerobic versus aerobic degradation of dimethyl sulfide and methanethiol in anoxic freshwater sediments.

Degradation of dimethyl sulfide and methanethiol in slurries prepared from sediments of minerotrophic peatland ditches were studied under various conditions. Maximal aerobic dimethyl sulfide-degrading capacities (4.95 nmol per ml of sediment slurry. h-1), measured in bottles shaken under an air atmosphere, were 10-fold higher than the maximal anaerobic degrading capacities determined from bottles shaken under N2 or H2 atmosphere (0.37 and 0. 32 nmol per ml of sediment slurry. h-1, respectively). Incubations under experimental conditions which mimic the in situ conditions (i. e., not shaken and with an air headspace), however, revealed that aerobic degradation of dimethyl sulfide and methanethiol in freshwater sediments is low due to oxygen limitation. Inhibition studies with bromoethanesulfonic acid and sodium tungstate demonstrated that the degradation of dimethyl sulfide and methanethiol in these incubations originated mainly from methanogenic activity. Prolonged incubation under a H2 atmosphere resulted in lower dimethyl sulfide degradation rates. Kinetic analysis of the data resulted in apparent Km values (6 to 8 microM) for aerobic dimethyl sulfide degradation which are comparable to those reported for Thiobacillus spp., Hyphomicrobium spp., and other methylotrophs. Apparent Km values determined for anaerobic degradation of dimethyl sulfide (3 to 8 microM) were of the same order of magnitude. The low apparent Km values obtained explain the low dimethyl sulfide and methanethiol concentrations in freshwater sediments that we reported previously. Our observations point to methanogenesis as the major mechanism of dimethyl sulfide and methanethiol consumption in freshwater sediments.

Aerobiosis↗

PubMed2000

Isolation and characterization of diverse halobenzoate-degrading denitrifying bacteria from soils and sediments.

Denitrifying bacteria capable of degrading halobenzoates were isolated from various geographical and ecological sites. The strains were isolated after initial enrichment on one of the monofluoro-, monochloro-, or monobromo-benzoate isomers with nitrate as an electron acceptor, yielding a total of 33 strains isolated from the different halobenzoate-utilizing enrichment cultures. Each isolate could grow on the selected halobenzoate with nitrate as the terminal electron acceptor. The isolates obtained on 2-fluorobenzoate could use 2-fluorobenzoate under both aerobic and denitrifying conditions, but did not degrade other halobenzoates. In contrast, the 4-fluorobenzoate isolates degraded 4-fluorobenzoate under denitrifying conditions only, but utilized 2-fluorobenzoate under both aerobic and denitrifying conditions. The strains isolated on either 3-chlorobenzoate or 3-bromobenzoate could use 3-chlorobenzoate, 3-bromobenzoate, and 2- and 4-fluorobenzoates under denitrifying conditions. The isolates were identified and classified on the basis of 16S rRNA gene sequence analysis and their cellular fatty acid profiles. They were placed in nine genera belonging to either the alpha-, beta-, or gamma-branch of the Proteobacteria, namely, Acidovorax, Azoarcus, Bradyrhizobium, Ochrobactrum, Paracoccus, Pseudomonas, Mesorhizobium, Ensifer, and Thauera. These results indicate that the ability to utilize different halobenzoates under denitrifying conditions is ubiquitously distributed in the Proteobacteria and that these bacteria are widely distributed in soils and sediments.

Benzoates↗

PubMed2001

Isolation, characterization, and polyaromatic hydrocarbon degradation potential of aerobic bacteria from marine macrofaunal burrow sediments and description of Lutibacterium anuloederans gen. nov., sp. nov., and Cycloclasticus spirillensus sp. nov.

Two new polyaromatic hydrocarbon-degrading marine bacteria have been isolated from burrow wall sediments of benthic macrofauna by using enrichments on phenanthrene. Strain LC8 (from a polychaete) and strain M4-6 (from a mollusc) are aerobic and gram negative and require sodium chloride (>1%) for growth. Both strains can use 2- and 3-ring polycyclic aromatic hydrocarbons as their sole carbon and energy sources, but they are nutritionally versatile. Physiological and phylogenetic analyses based on 16S ribosomal DNA sequences suggest that strain M4-6 belongs to the genus Cycloclasticus and represents a new species, Cycloclasticus spirillensus sp. nov. Strain LC8 appears to represent a new genus and species, Lutibacterium anuloederans gen. nov., sp. nov., within the Sphingomonadaceae. However, when inoculated into sediment slurries with or without exogenous phenanthrene, only L. anuloederans appeared to sustain a significant phenanthrene uptake potential throughout a 35-day incubation. In addition, only L. anuloederans appeared to enhance phenanthrene degradation in heavily contaminated sediment from Little Mystic Cove, Boston Harbor, Boston, Mass.

Aerobiosis↗