SEARCH · PubMed Health

Results for “Geologic Sediments”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources

PubMed2001

Heavy metal anomalies in lagoon sediments related to intensive agriculture in Altata-Ensenada del Pabellón coastal system (SE Gulf of California).

Heavy metal concentrations were examined in surface sediments from 79 sites within the Altata-Ensenada del Pabellon lagoon system. Data were normalized to separate natural from anthropogenic factors using aluminum and lithium as conservative elements and following two different discriminating criteria. For the normalization process, the natural metal concentrations were assumed to vary consistently with aluminum and lithium, unless the metal contents were of human origin. Strong linear correlations (P < .001) were observed between the conservative elements and the metals measured. According to Szefer's normalizing criteria, about 90% of the polluted sites, for at least one metal, occurred near agricultural discharge drains. In accordance with the Muller [Umschau 79 (1979) 778.] scale, this lagoon system is subject to pollutant effects only with regard to Pb (moderately to strongly polluted). It was concluded that either Al and Li could be useful to normalize granulometric variability in heavy metal studies of these lagoon sediments, and that Summers' normalization criterion proved more rigorous than Szefer's for these types of sediments.

Agriculture↗

PubMed2001

Method for enumeration of 5-cyano-2,3-ditoyl tetrazolium chloride (CTC)-active cells and cell-specific CTC activity of benthic bacteria in riverine, estuarine and coastal sediments.

Bacteria are the most abundant and active organisms in marine sediments and are critical for nutrient cycling and as a food source to many benthic and pelagic organisms. Bacteria are found both as free-living cells and as particle-associated cells, which can make investigations of these communities difficult. We found that common procedures for extracting bacteria from sediments leave the bacteria clay particle-associated and the clay particles clump, which reduce the reproducibility of direct counts. We optimized a sonication/surfactant method that produces a homogeneous suspension of bacterial cells against a uniform background of clay particles, which results in reproducible samples for epifluorescence microscopy. We developed a method to estimate CTC-positive cells and cell-specific CTC content in intact cores of surficial sediment communities from riverine, estuarine and coastal sites. Benthic bacterial abundances averaged 4.9x10(8) cells/g dry wt sediments in Apalachicola River, Florida sediments, 4.9-13.8x10(9) cells/g dry wt sediments in a variety of Apalachicola Bay sediments and 3.6x10(8) cells/g dry weight in shallow, anoxic Gulf of Mexico sediments. Percent CTC-positive cells ranged from low values of 9-10% CTC-positive cells in Apalachicola River and Apalachicola Bay sediments to high values of 25% CTC-positive cells in anoxic Gulf of Mexico sediments. After correction for abiotic CTC reduction and chlorophyll interference, estimates of cell-specific CTC reduction ranged from 0.15 to 0.55 fmol CTC(red)/active cell in the Apalachicola Bay sediments to 1.6 to 3.8 fmol CTC(red)/active cell in anoxic Gulf of Mexico sediments.

Bacteria↗

PubMed2004

Dynamic model for the accumulation of cadmium and zinc from water and sediment by the aquatic oligochaete, Tubifex tubifex.

In aquatic environments, organisms are exposed to and accumulate metals via waterborne and dietary routes including ingested sediment. A key element in understanding metal uptake and accumulation is information concerning the relative importance of the routes of uptake and the kinetics of the processes. In this work the bioaccumulation of the essential element zinc and the nonessential element cadmium were studied from the aqueous and sediment phase, in the cosmopolitan oligochaete Tubifex tubifex, using the radiotracers 109Cd and 65Zn. A compartmental kinetic model was constructed and parametrized by fitting the model to metal body concentrations. Using the pharmacokinetic modeling approach and taking into account the distribution of the metal between water and sediment, the different routes were quantitatively separated. Under the experimental conditions, the sediment phase accounted for 9.8% of the cadmium and 52% of the zinc uptake. These values are based on the uptake of the radiotracers spiked sediments and therefore likely represent maximal values since it was shown that under the specific conditions this was the most mobile metal fraction. This difference was largely explained by the large difference in assimilation efficiency between cadmium and zinc. Simulations of different conditions showed that both dissolved and sediment-associated metal can be important sources of metal exposure for the worms and that the relative importance strongly depends on the metal and exposure conditions including the lability of the metals in the sediment phase.

Animals↗

PubMed2004

Sediment and porewater profiles and fluxes of mercury and methylmercury in a small seepage lake in northern Minnesota.

Mercury (HgT) and methylmercury (MeHg) were measured at 1-2 cm resolution in sediment porewater and sediment cores from Spring Lake in the Marcell Experimental Forest of northern Minnesota. Recent sediment accumulation of HgT was 21.4 microg m(-2) yr(-1) (1990-2000), 2 orders of magnitude greater than the accumulation of MeHg (0.20 microg m(-2) yr(-1)). The highest solid phase concentrations of MeHg were observed persistently at the sediment surface and declined sharply with depth. Porewater profiles showed a small diffusive flux of MeHg from sediment to water (5 ng m(-2) month(-1)). Springtime porewater concentrations of MeHg were relatively low (approximately 0.5 ng L(-1)) and increased by late summer to early fall (1.5-2.2 ng L(-1)), showing distinct peaks roughly correlated with maxima in sulfate reducing activity at 5 and 15 cm. Advective transport carrying MeHg deeper into the sediment was evident in summer and fall. The percent of HgT present as MeHg was highest in the water column above the sediment (10%) and decreased with sediment depth in both the solid and porewater phases. Sediments at this study site are a net sink for MeHg, although diagenetic processes of demethylation and methylation are evident within the lake-sediment environment.

Environmental Monitoring↗

PubMed2006

Calculation and uses of mean sediment quality guideline quotients: a critical review.

Fine-grained sediments contaminated with complex mixtures of organic and inorganic chemical contaminants can be toxic in laboratory tests and/or cause adverse impacts to resident benthic communities. Effects-based, sediment quality guidelines (SQGs) have been developed over the past 20 years to aid in the interpretation of the relationships between chemical contamination and measures of adverse biological effects. Mean sediment quality guideline quotients (mSQGQ) can be calculated by dividing the concentrations of chemicals in sediments by their respective SQGs and calculating the mean of the quotients for the individual chemicals. The resulting index provides a method of accounting for both the presence and the concentrations of multiple chemicals in sediments relative to their effects-based guidelines. Analyses of considerable amounts of data demonstrated that both the incidence and magnitude of toxicity in laboratory tests and the incidence of impairment to benthic communities increases incrementally with increasing mSQGQs. Such concentration/response relationships provide a basis for estimating toxicological risks to sediment-dwelling organisms associated with exposure to contaminated sediments with a known degree of accuracy. This sediment quality assessment tool has been used in numerous surveys and studies since 1994. Nevertheless, mean SQGQs have some important limitations and underlying assumptions that should be understood by sediment quality assessors. This paper provides an overview of the derivation methods and some of the principal advantages, assumptions, and limitations in the use of this sediment assessmenttool. Ideally, mean SQGQs should be included with other measures including results of toxicity tests and benthic community surveys to provide a weight of evidence when assessing the relative quality of contaminated sediments.

Animals↗

PubMed1999

Release of atrazine ((14)C) from two undisturbed submerged sediments over a two-year period.

Through water erosion and runoff, sediment-adsorbed atrazine can undergo sedimentation and accumulation at the bottom of water bodies and become potential sources of atrazine to the water column. The purpose of this study is to determine the fate and release of atrazine ((14)C) to the water column from two simulated undisturbed submerged sediments at two temperature treatments (5 and 24 degrees C) over a 2-year period. Atrazine residue ((14)C) was released from the two sediments and was, primarily, diffusing from the sediment pore water to the water columns. The amount released was affected by sediment type and is related to the sediment's adsorption/desorption capacity. Larger amounts of residue ((14)C) were released to the water columns at 5 degrees C than at 24 degrees C. Atrazine degraded in the shallow submerged anaerobic sediment's water columns over the 2-year period. Less than 2% (percent of applied in atrazine equivalent) of extractable atrazine and metabolites remained in the sediment after 2 years. The amount of nonextractable atrazine residue ((1)(4)C) was significantly higher in sediments at 24 degrees C than at 5 degrees C. In conclusion, atrazine accumulating in shallow undisturbed submerged sediments from nonpoint sources would most likely degrade and/or become nonextractable over time and would have a low probability of becoming a significant source to the water body. The conditions where accumulation and future release of atrazine have a greater potential to occur are under very cold temperatures with low adsorption capacity sediments.

Atrazine↗

PubMed2004

The impact of ballast water effluent on the Manila clam, Tapes semidecussatus.

The impact of ballast water discharge from an oil refinery in Whitegate Harbour, Co. Cork, Ireland to the Manila clam, Tapes semidecussatus, was investigated using a whole sediment bioassay. Bioassay organisms were exposed to surface sediments for a period of 21 days, including a reference and control sediment, collected from the vicinity of a ballast water discharge pipe. At the whole organism level, mortality and burrowing behaviour (assessed as time taken for organisms to burrow into the sediment) were used to determine the effects of exposure to test sediments. After 21 days, clam mortality was higher in surface sediments collected directly at the point of the ballast water discharge pipe than from all other test sediments assayed. After 10 days exposure to test sediments collected from the vicinity of the ballast water discharge pipe, the burrowing behaviour of animals was significantly different to the behaviour of animals exposed to uncontaminated sediments.

Animals↗

PubMed2006

Development of a dynamic aquatic model (DynA Model): estimating temporal emissions of DDT to Lake Maggiore (N. Italy).

BACKGROUND, AIMS AND SCOPE: Most existing models used to describe the fate of chemicals in surface water and sediment generally consider a 'static scenario', in which a contaminant is discharged at a constant rate and environmental input parameters do not change during the simulation time. This approach is not suitable in environmental scenarios characterized by daily or periodic changes of several input parameters. The aim of this study is to estimate approximate emissions of DDT lo Lake Maggiore using a new surface water model, (DynA Model) that describes the fate of a chemical in a dynamic scenario. METHODS: The model is developed on the grounds of an existing and validated model (QWASI). A numerical solution was adopted to build the fully dynamic version of the model. RESULTS AND DISCUSSION: The model was applied to Lake Maggiore emitting DDT at a constant rate until steady-state was reached. Emissions were stopped and later sporadic 'pulse' emissions were added. This was done to calculate the amount of DDT needed to simulate concentrations close to those measured in water and sediments. This allowed the evaluation of the order of magnitude of emissions. An uncertainty analysis for sediment resuspension was also performed, given the lack of measured resuspension rates. CONCLUSION: The model showed the time response of the Lake Maggiore system to varying emission scenarios and provided what are regarded as reasonable estimates of DDT emissions. The model demonstrated the importance of sediment-water exchange. RECOMMENDATION AND OUTLOOK: In order to better calculate DDT concentrations the model should be run with different discharge scenarios to clarify the time trends of concentrations, possibly with the use of different sets of measured data (such as biota and sediment deposition/resuspension rates).

DDT↗

PubMed2005

Bio/chemical analysis of dioxin-like compounds in sediment samples from Osaka Bay, Japan.

The combinatorial bio/chemical investigation of sediments (six surface samples and one core sample) from Osaka Bay, Japan was conducted to clarify the horizontal and vertical distribution profiles of persistent organic pollutants in the sediments. Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), and polybrominated diphenylethers (PBDEs) were determined by chemical analysis and compared to bioassay results using H4IIE-luc/Dioxin Responsive-Chemical Activated LUciferase eXpression (DR-CALUX). For surface sediments, World Health Organization-toxicity equivalent (WHO-TEQ) values ranged from 1.8 to 92 pg g(-1) dry weight and the bioassay-TEQ (CALUX-TEQ) values (3.7-140 pg g(-1) dry weight) yielded significant correlation with them (r2 = 0.96). On the other hand, correlation between both TEQs (for WHO-TEQ, 5.5-47 and for CALUX-TEQ, 27-76 pg g(-1) dry weight) for core samples was not so good (r2 = 0.46). Comparing the vertical profiles of CALUX-TEQ and WHO-TEQ, they were different in that WHO-TEQ reached the maximum in the 1957 core section, while CALUX-TEQ reached in the 1984 core section. CALUX-TEQ values were 1-5-fold more than WHO-TEQ values in all the surface and core samples. CALUX-TEQ values were calculated for PBDE and PBDD/F concentrations, employing their CALUX toxicity equivalent factors (CALUX-TEFs). The estimated CALUX-TEQ values obtained for the brominated compounds could explain for 11% on average (range 4.7-31%) of the experimentally obtained CALUX-TEQ values in the investigated surface sediments.

Benzofurans↗

PubMed2000

The impact of plutonium speciation on the distribution coefficients in a sediment-sea water system, and radiological assessment of doses to humans.

When radionuclides are released from a source into the marine environment, the assessment of long term consequences to humans depends on information on the source term, transport in water, interactions with sediments (KD) and biological uptake (CF). Sensitivity analysis of assessment models demonstrates that KD is one of the most sensitive parameters contributing to large uncertainties in the assessment. Furthermore, the interaction of Pu-species with sediments is a time and temperature dependent process. The distribution coefficient, Bq kg(-1) sediment per Bq L(-1) sea water, increases with time until pseudo-equilibrium/equilibrium is reached (KD). Thus, the contact time between contaminated sea water and sediments should be taken into account in dispersion and dose assessment models. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a sediment-sea water system to obtain information on KD's. After a defined contact time, the samples have been sequentially extracted to determine mobile and bound fractions. The results indicate that the distribution coefficient, KD, for plutonium depends on Pu-species in question. Thus, sediments act as a sink for Pu(III, IV) (high KD), while Pu(III, IV)-organic and Pu(V, VI) should be considered more mobile (low KD). Furthermore, the interaction with inert fractions obtained from sequential extraction depends less on Pu-species but increase with time. For short time interactions, species-specific time functions rather than KD constants should be applied in assessment models. When the accepted KD (10(5) L kg(-1)) is implemented in the model, the estimated collective dose is about 8 x 10(-4) person-Sv, i.e., a factor of about 2 lower than for Pu(III, IV)-organic and Pu(V, VI). So changes in KD have an impact on the assessment of collective dose received from a potential release of plutonium from fallout, reactor accidents, etc., which underlines the need for more detailed studies on speciation, kinetics, and KD's in different sediment-sea water systems.

Acetates↗

PubMed2007

In vitro cell growth of marine archaeal-bacterial consortia during anaerobic oxidation of methane with sulfate.

Anoxic sediment from a methane hydrate area (Hydrate Ridge, north-east Pacific; water depth 780 m) was incubated in a long-term laboratory experiment with semi-continuous supply of pressurized [1.4 MPa (14 atm)] methane and sulfate to attempt in vitro propagation of the indigenous consortia of archaea (ANME-2) and bacteria (DSS, Desulfosarcina/Desulfococcus cluster) to which anaerobic oxidation of methane (AOM) with sulfate has been attributed. During 24 months of incubation, the rate of AOM (measured as methane-dependent sulfide formation) increased from 20 to 230 micromol day(-1) (g sediment dry weight)(-1) and the number of aggregates (determined by microscopic counts) from 0.5 x 10(8) to 5.7 x 10(8) (g sediment dry weight)(-1). Fluorescence in situ hybridization targeting 16S rRNA of both partners showed that the newly grown consortia contained central archaeal clusters and peripheral bacterial layers, both with the same morphology and phylogenetic affiliation as in the original sediment. The development of the AOM rate and the total consortia biovolume over time indicated that the consortia grew with a doubling time of approximately 7 months (growth rate 0.003 day(-1)) under the given conditions. The molar growth yield of AOM was approximately 0.6 g cell dry weight (mol CH(4) oxidized)(-1); according to this, only 1% of the consumed methane is channelled into synthesis of consortia biomass. Concentrations of biomarker lipids previously attributed to ANME-2 archaea (e.g. sn-2-hydroxyarchaeol, archaeol, crocetane, pentamethylicosatriene) and Desulfosarcina-like bacteria [e.g. hexadecenoic-11 acid (16:1omega5c), 11,12-methylene-hexadecanoic acid (cy17:0omega5,6)] strongly increased over time (some of them over-proportionally to consortia biovolume), suggesting that they are useful biomarkers to detect active anaerobic methanotrophic consortia in sediments.

Anaerobiosis↗

PubMed2000

Horizontal heterogeneity of denitrifying bacterial communities in marine sediments by terminal restriction fragment length polymorphism analysis.

Although it is widely believed that horizontal patchiness exists in microbial sediment communities, determining the extent of variability or the particular members of the bacterial community which account for the observed differences among sites at various scales has not been routinely demonstrated. In this study, horizontal heterogeneity was examined in time and space for denitrifying bacteria in continental shelf sediments off Tuckerton, N.J., at the Rutgers University Long-Term Ecosystem Observatory (LEO-15). Characterization of the denitrifying community was done using PCR amplification of the nitrous oxide reductase (nosZ) gene combined with terminal restriction fragment length polymorphism analysis. Spatial scales from centimeters to kilometers were examined, while temporal variation was assayed over the course of 1995 to 1996. Sorenson's indices (pairwise similarity values) were calculated to permit comparison between samples. The similarities of benthic denitrifiers ranged from 0.80 to 0.85 for centimeter scale comparisons, from 0.52 to 0.79 for meter level comparisons, and from 0.23 to 0.53 for kilometer scale comparisons. Sorenson's indices for temporal comparisons varied from 0.12 to 0.74. A cluster analysis of the similarity values indicated that the composition of the denitrifier assemblages varied most significantly at the kilometer scale and between seasons at individual stations. Specific nosZ genes were identified which varied at centimeter, meter, or kilometer scales and may be associated with variability in meio- or macrofaunal abundance (centimeter scale), bottom topography (meter scale), or sediment characteristics (kilometer scale).

Cluster Analysis↗

PubMed2002

2-Ethyl-3-methylmaleimide in Tokyo Bay sediments providing the first evidence for its formation from chlorophylls in the present photic and oxygenic zone.

Tokyo Bay bottom sediments were analyzed for 2-ethyl-3-methylmaleimide, a degradation product of chlorophylls, which has been detected in ancient sediments. It was found in all sediments examined in concentrations of about 1 to 15 nmol/g- of dried sediment, and it was shown to be preserved for 100 years in the sediments. Its depth distribution agreed with that of the reported total organic carbon content of the sediments, reflecting a change in primary productivity. We concluded that this maleimide was produced under photic and oxygenic conditions in nature before the incorporation of photosynthesizing organisms into sediments.

Chlorophyll↗

PubMed2004

Model-aided characterization of Tenax-TA for aromatic compound uptake from water.

The polymer adsorbent Tenax has been widely employed for studying desorption of organic contaminants in soils and sediments and for correlating physical availability with bioavailability. Although Tenax has been invoked to act as an infinite sink that completely and instantaneously removes solutes from the aqueous phase, to our knowledge no systematic characterization of Tenax resins has been carried out. The present study provides equilibrium and kinetic parameters for the uptake of benzene, nitrobenzene, naphthalene, phenanthrene, and pyrene by Tenax in selected water-solute-Tenax systems, and it offers guidelines for the use of Tenax resins. Sorption isotherms of the test compounds on Tenax-TA are nonlinear, and most show an inflection at high concentration, marking a change in physical state from glassy to rubbery. A simple dual-mode model was applied to the isotherms below the apparent inflection point. Sorption parameters for dissolution and hole-filling domains each correlate with the octanol-water partition coefficient. The effects of dissolved organic matter and salinity on Tenax-TA uptake are minor. Regeneration of Tenax-TA by hot-methanol extraction increased its affinity for naphthalene. Inclusion of 23% graphitized carbon in the polymer reduced affinity for phenanthrene. Uptake rate data were fit by the dual-mode diffusion model, which assumes diffusion in the polymer matrix. The obtained diffusion rate parameter correlates with molecular size. Equilibrium and kinetic parameters for benzene and nitrobenzene were comparable despite a three-orders-of-magnitude difference in their Henry's law coefficients, indicating that a pathway to the Tenax surface through the vapor phase is not required. Extrapolating to typical conditions in soil-desorption studies reveals that single-solute uptake is 95% or more complete within 4 min for the test compounds and within 7 min for benzo[a]pyrene. Thus, Tenax is suitable for compounds with desorption from soil or sediment that occurs over comparably longer timescales.

Adsorption↗

PubMed2006

Measurement of total polycyclic aromatic hydrocarbon concentrations in sediments and toxic units used for estimating risk to benthic invertebrates at manufactured gas plant sites.

The U.S. Environmental Protection Agency's (U.S. EPA) narcosis model requires the measurement of 18 parent and 16 groups of alkyl polycyclic aromatic hydrocarbons (PAHs) (so-called 34 PAHs) in sediments to calculate the number of PAH toxic units (TU) available to benthic organisms. If data for the 34 PAHs are not available, the U.S. EPA proposes estimating the risk by multiplying the TU for 13 parent PAHs by 11.5 (95% confidence interval) based on data from 488 sediments. This estimate is overly conservative for PAHs from pyrogenic manufactured gas plant (MGP) processes based on the analysis of 45 sediments from six sites. Parent PAHs contributed approximately 40% of the total concentrations and TU for MGP sediments. In contrast, parent PAHs from diesel fuel and petroleum crude oil contributed only 2 and 1%, respectively, of the PAH concentrations and TU, compared to approximately 98 to 99% contributed by the alkyl PAHs. Statistical comparison of the TU based on the measured 34 alkyl and parent PAHs and those based on only 13 parent PAHs demonstrated that a factor of 4.2 (rather than 11.5) is sufficient to estimate total TU within a 95% confidence level for MGP sites. Similarly, measurement of parent PAHs is sufficient to accurately estimate the total 34 alkyl and parent PAH concentrations for MGP-impacted sediments.

Animals↗

PubMed2006

Measured partitioning coefficients for parent and alkyl polycyclic aromatic hydrocarbons in 114 historically contaminated sediments: part 1. K(OC) values.

Polycyclic aromatic hydrocarbon (PAH) partitioning coefficients between sediment organic carbon and water (K(OC)) values were determined using 114 historically contaminated and background sediments collected from eight different rural and urban waterways in the northeastern United States. More than 2100 individual K(OC) values were measured in quadruplicate for PAHs ranging from two to six rings, along with the first reported K(OC) values for alkyl PAHs included in the U.S. Environmental Protection Agency's (U.S. EPA) sediment narcosis model for the prediction of PAH toxicity to benthic organisms. Sediment PAH concentrations ranged from 0.2 to 8600 microg/g (U.S. EPA 16 parent PAHs), but no observable trends in K(OC) values with concentration were observed for any of the individual PAHs. Literature K(OC) values that are commonly used for environmental modeling are similar to the lowest measured values for a particular PAH, with actual measured values typically ranging up to two orders of magnitude higher for both background and contaminated sediments. For example, the median log K(OC) values we determined for naphthalene, pyrene, and benzo[a]pyrene were 4.3, 5.8, and 6.7, respectively, compared to typical literature K(OC) values for the same PAHs of 2.9, 4.8, and 5.8, respectively. Our results clearly demonstrate that the common practice of using PAH K(OC) values derived from spiked sediments and modeled values based on n-octanol-water coefficients can greatly overestimate the actual partitioning of PAHs into water from field sediments.

Carbon↗

PubMedDate not supplied

Effect of nutrient amendments on indigenous hydrocarbon biodegradation in oil-contaminated beach sediments.

Nutrient amendment to oil-contaminated beach sediments is a critical factor for the enhancement of indigenous microbial activity and biodegradation of petroleum hydrocarbons in the intertidal marine environment. In this study, we investigated the stimulatory effect of the slow-release fertilizers Osmocote (Os; Scotts, Marysville, OH) and Inipol EAP-22 (Ip; ATOFINA Chemicals, Philadelphia, PA) combined with inorganic nutrients on the bioremediation of oil-spiked beach sediments using an open irrigation system with artificial seawater over a 45-d period. Osmocote is comprised of a semipermeable membrane surrounding water-soluble inorganic N, P, and K. Inipol, which contains organic N and P, has been used for oil cleanup on beach substrate. Nutrient concentrations and microbial activity in sediments were monitored by analyzing sediment leachates and metabolic dehydrogenase activity of the microbial biomass, respectively. Loss of aliphatics (n-C12 to n-C33, pristane, and phytane) was significantly greater (total loss between 95 and 97%) in oil-spiked sediments treated with Os alone or in combination with other nutrient amendments, compared with an unamended oil-spiked control (26% loss) or sediments treated with the other nutrient amendments (28-65% loss). A combination of Os and soluble nutrients (SN) was favorable for the rapid metabolic stimulation of the indigenous microbial biomass, the sustained release of nutrients, and the enhanced biodegradation of petroleum hydrocarbons in leached, oil-contaminated sediments.

Bacteria↗

PubMed2006

Effects of plants on the removal of hexavalent chromium in wetland sediments.

The effect of two wetland plants, Typha latifolia L. (cattail) and Phragmites australis (Cav.) Trin. ex Steud (common reed), on the fate of Cr(VI) in wetland sediments was investigated using greenhouse bench-scale microcosm experiments. The removal of Cr(VI) was monitored based on the vertical profiles of aqueous Cr(VI) in the sediments. The Cr(VI) removal rates were estimated taking into account plant transpiration, which was found to significantly concentrate dissolved species in the sediments. After correcting for evapotranspiration, the actual Cr(VI) removal rates were significantly higher than would be inferred from uncorrected profiles. On average, the Cr(VI) removal rates were 0.005 to 0.017 mg L(-1) d(-1), 0.0003 to 0.08 mg L(-1) d(-1), and 0.004 to 0.13 mg L(-1) d(-1) for the control, T. latifolia, and P. australis microcosms, respectively. The fate of the removed Cr(VI) was examined by determining the quantity and chemical speciation of the Cr in the sediment and plant materials. Chromium(III) was the dominant form of Cr in both the sediment and plants, and precipitation of Cr(III) in the sediment was the major pathway responsible for the disappearance of aqueous Cr(VI) from the pore water. Incubation results showed that abiotic reduction was the primary mechanism underlying Cr(VI) removal in the microcosm sediments. Organic compounds produced by plants, including root exudates and mineralization products of dead roots, are thought to be the factor that is either directly or indirectly responsible for the gap between Cr(VI) removal efficiencies in the sediments of the vegetated and unvegetated microcosms.

Chromium↗