Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Sediment”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 289 records · Page 16Linked to original sources
PubMed1998

Sedimentation of free and attached Cryptosporidium oocysts and Giardia cysts in water.

Experimental analysis of the sedimentation velocity of Cryptosporidium parvum oocysts and Giardia lamblia cysts was compared with mathematical description of their sedimentation velocities by using measurements of (oo)cyst size and density and the density and viscosity of the sedimentation medium to determine if the sedimentation kinetics of freely suspended oocysts of C. parvum and cysts of G. lamblia can be described by Stokes' law. The theoretically calculated sedimentation kinetics showed a good agreement with the experimentally observed kinetics. Both showed a decline in sedimentation velocity over time, caused primarily by variation in (oo)cyst density. The initial apparent sedimentation velocities in Hanks balanced salt solution at 23 degrees C was 0.35 micron . s-1 for oocysts and 1.4 micron . s-1 for cysts. (Oo)cysts that enter the surface water environment by discharges of biologically treated sewage may be attached to sewage particles, and this will affect their sedimentation kinetics. Therefore, (oo)cysts were mixed with settled secondary effluent. (Oo)cysts readily attached to the (biological) particles in effluent; 30% of both cysts and oocysts attached during the first minutes of mixing, and this fraction increased to approximately 75% after 24 h. The sedimentation velocity of (oo)cysts attached to secondary effluent particles increased with particle size and was (already in the smallest size fraction [1 to 40 micron]) determined by the sedimentation kinetics of the effluent particles. The observed sedimentation velocities of freely suspended (oo)cysts are probably too low to cause significant sedimentation in surface water or reservoirs. However, since a significant proportion of both cysts and oocysts attached readily to organic biological particles in secondary effluent, sedimentation of attached (oo)cysts after discharge into surface water will probably be a significant factor in the environmental ecology of C. parvum and G. lamblia. Attachment to particles influences not only sedimentation of (oo)cysts in surface water but also their behavior in drinking water treatment processes.

Animals↗
PubMed2001

The relevance of rooted vascular plants as indicators of estuarine sediment quality.

Toxicity assessments and numerical quality assessment guidelines for estuarine sediments are rarely based on information for aquatic plants. The effect of this lack of information on contaminated sediment toxicity evaluations is largely unknown. For this reason, the toxicities of whole sediments collected from 15 sites in three urbanized Florida bayou-estuaries were determined for the benthic invertebrates Mysidopsis bahia and Ampelisca abdita and the plants Scirpus robustus Pursh (saltmarsh bulrush) and Spartina alterniflora Loisel (saltmarsh cordgrass). The results of the bioassays, conducted for 7 to 28 days, were compared for interspecific differences and to effects-based, sediment quality assessment guidelines. A variety of inorganic and organic analytes were detected in the estuarine sediments, and concentrations of as many as 7 analytes exceeded the sediment guidelines at the 15 sampling locations. Toxicity occurred at 2 of the 15 sampling stations based on invertebrate survival. Twelve of the 15 sediments had either a significant stimulatory or inhibitory effect on early seedling growth relative to a reference sediment (p < 0.05). The phytoresponse was specific to the location, test species, and plant tissue. There was no consistent trend between the sensitivities of the plants and invertebrates exposed to the sediments collected from the same sites. Of the 12 sediments that significantly affected seedling growth, 10 were not acutely toxic to the invertebrates. Consequently, the plant test species provided information that would have been missing if only animal test species were used. For this reason, the phytotoxicity database needs to be expanded for contaminated sediments to further evaluate interspecific sensitivities and to provide perspective on the environmental relevancy of proposed sediment quality criteria and effects-based assessment guidelines for which this information is usually missing. However, additional test method development and field validation are needed to support this effort, which includes the identification of sensitive plant test species, response parameters, and the chemical and physical sediment factors that influence plant growth.

Animals↗
PubMed2006

Variation of metals in bed sediments of Qaraaoun Reservoir, Lebanon.

The Qaraaoun Reservoir (impoundment of the River Litani) is the only artificial surface water body in the country, Lebanon. Earlier study on the water quality of the Qaraaoun Reservoir identified three water quality zoning with a central distinct zone suitable for multipurpose water usage. The objective of this study was to extend the earlier work by considering the total metal content of reservoir bed sediments and hence to evaluate factors that control metal deposition or capture. Water samples were collected from 15 sampling sites and sediment samples were simultaneously collected from 9 sites. Water parameters analyzed were pH, Eh, DO and temperature. Sediment samples were dried and sieved and sediment < 75 microm was retained for analysis. Sediments were subjected to a stepwise heating process with aqua regia to extract the metals, and their content in sediments determined by ICP-MS. The sediment data revealed higher metal contents where the river entered the reservoir which matched higher concentrations of water parameters at the influx site. Regression analysis of total metals in sediments with distance from the river Litani influx point to the dam revealed a log trend for Fe, Cr and Ni, whereas, the concentrations of Cu, Zn, Cd, Pb were better described by a polynomial regression. Three sediment zones were identified: entrance, oxidation (central) and reducing (near dam) zones. Sediment contents of Zn, Cu and Pb correlated with organic content, whereas sediment Cr and Ni were associated with iron. It was concluded that sediments act as a sink for metals and the deposition of metals is primarily related to sediment organic content and the level of dissolved oxygen in water.

Environmental Monitoring↗
PubMed2006

Biodegradation of polycyclic aromatic hydrocarbons in the natural waters of the Yellow River: effects of high sediment content on biodegradation.

The contamination of polycyclic aromatic hydrocarbons (PAHs) has become one of the major problems in the Yellow River of China. As the Yellow River is the most turbid large river in the world, it remains unknown to which extent the high suspended sediment content in the river may affect the fate and effect of PAHs. Here we report the effect of sediment on biodegradation of chrysene, benzo(a)pyrene and benzo(g,h,i)perylene with phenanthrene as a co-metabolism substrate in natural waters from the Yellow River. Biodegradation kinetics of the PAHs in the river water with various levels of sediment contents were studied in the laboratory by fitting with a biodegradation kinetics model for organic compounds not supporting growth. The results indicated that the biodegradation rates of PAHs increased with the sediment content in the water. When the sediment contents were 0, 4 and 10 g/l, the biodegradation rate constants of chrysene with the initial concentration of 3.80 microg/l were 0.053, 0.084 and 0.111 d(-1), respectively. Further studies suggested the enhanced biodegradation rate in the presence of sediment was caused by the following mechanisms: (1) the population of PAH-degrading bacteria in the water system was found to increase with the sediment content; the bacteria population on sediment phase was far greater than that on water phase during the cultivation process; (2) the sorption of PAHs on the sediment phase was well described by the dual adsorption-partition model. Although the sorption capacity of PAH per unit weight of sediment decreased with the increase of the sediment content, the amount of sorbed PAH increased with the sediment content; and, (3) the desorption of PAHs from the solid phase led to a higher concentration near the water-sediment interface. Since the bacteria were also attached to the interface, this resulted in an increased contact chance between the bacteria and PAHs.

Adsorption↗
PubMed2005

Sedimentation rates and erosion processes in the lagoon of Venice.

Since the early 1990s in the lagoon of Venice, especially in the central basin, the surface sediment underwent high re-suspension and sedimentation changes and water turbidity increased both because of the disappearance of the macroalgal coverage and the harvesting of the Manila clam Tapes philippinarum Adams and Reeve, which had rapidly colonised the bottom free of macrophytes. Clams are harvested with hydraulic and mechanical dredges which remove and re-suspend surface sediments causing the transport and loss of the finest materials. Sediment transport and re-deposition in the lagoon have been monitored with sediment traps placed onto the bottoms near the Malamocco mouth (st. A), the Lido watershed (st. B) and the mainland (sts. C and D). From 1989-1993 to 1998-1999 sedimentation rates increased significantly at st. A (from 41 to 228 kg DW m(-2) year(-1)), st. B (from 65 to 760 kg DW m(-2) year(-1)) and st. C (from 140 to 721 kg DW m(-2) year(-1)), while at st. D sedimentation rates increased only by ca. 20%. In parallel sediment grain-size changed with a loss of the finest fraction especially near the mainland. The erosion or sedimentation status, acquired by utilizing sedimentation devices placed onto the bottoms, showed that sts. B, C, D were affected by sediment losses, while st. A, populated by seagrasses and characterised by seasonal variations which depend on the shoot development, did not show any significant bathymetric change on an annual basis. The highest sediment erosion was recorded at st. D (ca. 3.6 cm year(-1)) whereas a loss of ca. 1.5 and 0.5 cm year(-1) was found at sts. C and B, respectively, which accounted for a mean loss in the central lagoon of ca. 1.2 million tonnes year(-1). Those data agree with the previous indirect estimation of sediment loss which was based on the number of fishing boats operating in the lagoon on an annual basis.

Animals↗
PubMed2005

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: II. Organism and population-level endpoints.

This study aimed to test the performance of the amphipod Gammarus locusta (L.) in chronic sediment toxicity tests. It constitutes part of a multi-level assessment of chronic toxicity of estuarine sediments, integrating organism and population-level endpoints with biochemical markers responses. Here we account for organism and population-level effects, while biomarker responses were reported in a companion article. Five moderately contaminated sediments from Sado and Tagus estuaries were tested, comprising 3 muddy and 2 sandy sediments. These sediments either did not show acute toxicity or were diluted with control sediment as much as required to remove acute toxicity. Subsequent chronic tests consisted of 28-day exposures with survival, individual growth and reproductive traits as endpoints. Two of the muddy sediments induced higher growth rates in the amphipods, and improved reproductive traits. This was understood to be a consequence of the amount of organic matter in the sediment, which was nutritionally beneficial to the amphipods, while concurrently decreasing contaminant bioavailability. Biomarker responses did not reveal toxicant-induced stress in amphipods exposed to these sediments. One of the sandy sediments was acutely toxic at 50% dilution, but in contrast stimulated amphipod growth when diluted 75%. This was presumed to be an indication of a hormetic response. Finally the two remaining contaminated sediments showed pronounced chronic toxicity, affecting survival and reproduction. The sex ratio of survivors was highly biased towards females, and offspring production was severely impaired. The particulars of the responses of this amphipod were examined, as well as strengths versus limitations of the sediment test. This study illustrates the utility of this chronic test for toxicity assessment of contaminated estuarine sediments, with potential application all along Atlantic Europe.

Amphipoda↗
PubMed2005

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: I. Biochemical endpoints.

We report on biomarker responses conducted as part of a multi-level assessment of the chronic toxicity of estuarine sediments to the amphipod Gammarus locusta. A companion article accounts for organism and population-level effects. Five moderately contaminated sediments from two Portuguese estuaries, Sado and Tagus, were assessed. Three of them were muddy and two were sandy sediments. The objective was to assess sediments that were not acutely toxic. Three of the sediments met this criterion, the other two were diluted (50% and 75%) with clean sediment until acute toxicity was absent. Following 28-d exposures, the amphipods were analysed for whole-body metal bioaccumulation, metallothionein induction (MT), DNA strand breakage (SB) and lipid peroxidation (LP). Two of the muddy sediments did not cause chronic toxicity. These findings were consistent with responses at organism and population levels that showed higher growth rates and improvement of reproductive traits for amphipods exposed to these two sediments. Two other sediments, one muddy and one sandy, exhibited pronounced chronic toxicity, affecting SB, MT induction (in muddy sediment), survival and reproduction. Potential toxicants involved in these effects were identified. The last sandy sediment exhibited some loss of DNA integrity, however growth was also enhanced. Present results, together with the organism/population-level data, and also benthic communities information, were analysed under a weight-of-evidence approach. By providing evidence of exposure (or lack of it) to contaminants in sediments, the biomarkers here applied assisted in distinguishing toxicants' impacts in test organisms from the confounding influence of other geochemical features of the sediments.

Amphipoda↗
PubMed2006

Chronic exposure of Leptocheirus plumulosus to Baltimore Harbor sediment: bioenergetic and population-level effects.

We investigated the long-term effects of contaminants in sediment from Baltimore Harbor, MD, USA, on a burrowing amphipod (Leptocheirus plumulosus) via a full life-cycle laboratory exposure. Contaminants in the Baltimore Harbor sediment included PAHs (10,800 ng/g), PCBs (152 ng/g), and heavy metals (including As, Cd, Cu, Pb, Hg, Ni, and Zn). Exposures were initiated with neonate amphipods, placed in microcosms containing either contaminated or reference sediment, and were maintained for 42 days, allowing ample time for the initial cohort to mature and reproduce. At the end of the exposure period, the populations of amphipods were surveyed to ascertain the number and size of amphipods in each size class (neonate, juvenile, and adult), and bioenergetic measurements were performed on adults, including metabolic rate, lipid content, and fecundity. Contaminated sediment from Baltimore Harbor caused lower growth and reproductive rates; in Baltimore Harbor sediment, the average dry weight of amphipod offspring in each size class was significantly lower and there were less than one-third as many individuals in each size class, compared to reference sediment. By the end of the exposure, the total amphipod biomass in Baltimore Harbor sediment was less than one quarter of that in reference sediment. On average, gravid females in reference sediment produced at least twice as many viable offspring as those in contaminated sediment. Adult male amphipods in Baltimore Harbor sediment possessed significantly lower lipid concentrations. Lipid content in neonates also appeared to be negatively affected by parental exposure to contaminants. Metabolic rate was elevated in adult amphipods exposed to Baltimore Harbor sediment. Overall, the results suggest that contaminated sediment conditions in the urban estuary may chronically affect L. plumulosus by diverting energy from production to maintenance pathways, resulting in slower growth and reduced fecundity, and ultimately leading to retarded population growth rates. The results of this study reinforce the need for long-term toxicological exposures to reveal chronic effects.

Amphipoda↗
PubMed2005

Kinetics of phosphorus release from a natural mixed grain-size sediment with associated algal biofilms.

Experiments using flumes containing mixed grain-size sediment with an associated algal biofilm, from two sites on the R. Tame, investigated the sediment-water exchanges in heterogeneous sediment deposits. These results were considered in the light of findings of a companion study [Gainswin BE, et al. The effects of sediment size fraction and associated algal biofilms on the kinetics of phosphorus release. Sci Total Environ, this issue.] by considering this natural system in relation to the effects of the different sizes of material comprising the sediment. Sediment samples were collected in trays installed in the river over a period of one growth cycle (March 2001-April 2002) and placed in flume channels with controlled water flow. The temperature, pH, and dissolved oxygen of the solution overlying the sediment were monitored automatically whilst filtered samples were obtained at 2-0h intervals over 48 h. The biomass, expressed as chlorophyll a, of the algal component of the biofilm from the surface of the sediment was estimated using methanol extraction. The composition of the sediment, viz. size fractions, organic matter and porosity, were determined at the end of the experiments. The equilibrium phosphate concentration and a phosphorus transfer index were used to establish that a net uptake of phosphorus by some of the samples that occurred at the time of sampling. The results were modelled using a Diffusion Boundary Layer model and the maximum flux from the sediment (or limiting diffusion flux) compared for each of the samples. The limiting diffusion flux was highest at the most contaminated site--reaching approximately 180 nmol m(-2) s(-1) (normalised with respect to the river bed area). The limiting diffusion flux calculated for the composite samples was in agreement with the flux estimated from the contributions expected from the individual size fractions [Gainswin BE, et al. The effects of sediment size fraction and associated algal biofilms on the kinetics of phosphorus release. Sci Total Environ, this issue.]. The dominance of the flux contribution from the stones size fraction (>20 mm) confirms that sediment having a filamentous biofilm and associated particulate material results in a greater flux than a silt sediment without such a biomass.

Biofilms↗
PubMed2001

Exploratory analysis of the effects of particulate characteristics on the variation in partitioning of nonpolar organic contaminants to marine sediments.

The partitioning of nonpolar organic contaminants to marine sediments is considered to be controlled by the amount of organic carbon present. However, several studies propose that other characteristics of sediments may affect the partitioning of contaminants. For this exploratory analysis, we measured 19 sediment characteristics from five marine sediments and 11 characteristics of humic acids extracted from the sediments. These characteristics included elemental composition, grain size, soot carbon, polarity indices and molar ratios. Each individual characteristic and combinations of these characteristics were then used to normalize partition coefficients (Kp) generated for three organic contaminants: lindane, fluoranthene and a tetrachlorinated biphenyl (PCB). A coefficient of variation (CV) was then calculated for each contaminant to determine which normalization characteristic (individually or in combination) resulted in the lowest variability in partitioning between study sediments. For lindane and the PCB. normalization by the amount of sediment organic carbon resulted in the lowest variability in partition coefficients with CVs of 16.2% and 37.7%. respectively. However, normalization of fluoranthene by silt content resulted in lower CVs than those generated by organic carbon normalization: 31.0% vs. 37.6%. Normalization of contaminants Kp's by combined values of sediment characteristics resulted in lower CVs but only by a few percent. Using humic acid characteristics, humic organic carbon reduced variability between sediments most effectively. But only the normalized fluoranthene values had a CV (i.e., 25.4%) lower than the one based on normalization by sediment characteristics. When combined, humic acid characteristics resulted in lower CVs than normalization by individual or combinations of sediment characteristics for fluoranthene and the PCB with CVs of 19.3% and 28.7%, respectively. This analysis indicates variability associated with the partitioning of some organic contaminants to marine sediments can be further reduced when normalization by sediment characteristics other than organic carbon are utilized.

Absorption↗
PubMed2002

Partitioning and bioaccumulation of cadmium in artificial sediment systems: application of a stable isotope tracer technique.

The utility of stable isotope tracers for investigating the relationship between cadmium (Cd) partitioning in artificial sediment-water systems and Cd accumulation in a benthic detritivore (Asellus racovitzai, Isopoda) was explored. In the laboratory, Cd isotopes were applied to synthetic sediment and isotope concentrations were measured in sediment, overlying water and exposed asellids over a 10-day period. Isotope ratios measured in sediment and water were compared to ratios measured in asellids to determine whether Cd partitioning could predict metal bioaccumulation. Two different parameters which might affect Cd partitioning between the sediment and overlying water compartments were investigated: the chemical form in which Cd was added to systems, and the organic matter content of the sediment. To test the effect of chemical form on Cd partitioning, three isotopes of cadmium were individually applied to formulated sediment in varying combinations of 113Cd(NO3)2, 112Cd-humic acid (HA) 114CdSO4. The results demonstrated that chemical form did not influence partitioning, as the Cd isotope that was applied to sediment in the nitrate form exhibited similar partitioning between sediment and overlying water as the isotope that was applied in the sulfate or HA form. However, Cd isotope concentrations in overlying water were strongly related to the pattern of isotope accumulation in asellids suggesting that overlying water concentrations determined Cd bioaccumulation. In contrast, when the organic matter content of sediment was increased through the addition of Sphagnum peat moss, total Cd concentrations in overlying water and tissue were low, and there was no relationship between Cd-isotope concentrations in tissue and water. These results indicate that Cd accumulation occurred primarily from water, and factors that increase metal partitioning to sediment, such as increased sediment organic matter content, decrease Cd accumulation in asellids. The stable isotope tracer method described herein appears to be a useful technique for investigating the relationship between metal partitioning and bioaccumulation in simple sediment systems, but could also be extended to more complex systems, and used with different metals that have multiple stable isotopes.

Animals↗
PubMed2002

Toxicity of sediments from around a North Sea oil platform: are metals or hydrocarbons responsible for ecological impacts?

Discharges of contaminated drill cuttings have caused appreciable ecological change of the benthos adjacent to many oil and gas platforms in the North Sea. Many platforms have large piles of cuttings lying beneath them and these probably present the greatest potential hazard to the environment during platform decommissioning and removal. There is, however, a lack of consensus on which aspects of drill cuttings are responsible for the adverse ecological effects. This hinders risk assessment of management options. Here we report data on the toxicity of sediments from around the North West Hutton platform to the amphipod Corophium volutator, the polychaete Arenicola marina and the Microtox" acute test system. Sediment was acutely toxic to Corophium out as far as 600 m from the platform. Sediment from 100 m from the platform remained acutely toxic to Corophium when 3% contaminated sediment was mixed with clean sediment. A 10% dilution of this sediment also inhibited Arenicola feeding almost completely. Sediment elutriates did not inhibit Microtox light output, but organics extracted by dichloromethane were very toxic. Fifteen minute EC50 values were as low as 0.25 mg ml(-1) and were strongly correlated with hydrocarbon concentrations. Metal concentrations in whole sediments were correlated with their toxicity to Corophium but the relationship was much weaker when data on dilutions were included. Except at sites immediately adjacent to the platform, metal concentrations were well below ERL values from the literature, so were too low to explain sediment toxicity. Toxicity of sediments to Corophium was closely correlated with their hydrocarbon content, even when tests on dilutions were included in the analysis. We conclude that hydrocarbons are the most significant cause of toxicity in these sediments contaminated with oil based drill cuttings and that polar organics, sulphide. ammonia and other water soluble substances are of much lower significance. Applying OSPAR guidelines to our data on the toxicity of cuttings pile material to Corophium data would give a maximum allowable concentration of 0.03% in clean sediments. The Microtox data indicate that sediments from deeper in the pile would require an even greater dilution than this.

Animals↗
PubMed2001

Changes in the leachability of metals from dredged canal sediments during drying and oxidation.

The behaviour of metals in canal sediments after their disposal to land has important implications for the environmental management of canal dredgings. The leaching behaviour of trace metals was investigated in a laboratory-based experiment using sediment from a canal in the UK (139 mg Zn kg-1dry sediment, 1.1 mg Cd, kg-1dry sediment 31.5 mg Cr kg-1dry sediment, 20.6 mg Cu kg-1dry sediment 48.4 mg Ni kg-1dry sediment, 43.4 mg Pb kg-1dry sediment and 7.6 mg As kg-1dry sediment). The sediment was allowed to dry. Cores (10 cm long) of the drying canal sediment were taken over a period of 12 weeks. A simple water extraction procedure was used to investigate changes in metal leachability at varying depths through the cores. Metal leachability increased over the first five weeks of drying and then subsequently decreased between weeks five and twelve, (e.g. Cd increased from approximately 0.006 to 0.018 mg/kgsediment then decreased to approximately 0.006 mg/kgsediment, Zn increased from approximately 1.5 to 3 mg/kgsediment and then decreased to approximately 1.5 mg/kgsediment). These results were combined with sulphide/sulphate ratios, which showed a decrease as the sediment dried (e.g. at 2-4 cm depth from approximately 1 to 0.49), and BCR sequential extraction data. Most metals (except Cd and As) showed a redistribution from the residual phase into more mobile phases as the sediment dried and oxidised. Metal leachability was strongly correlated with the sulphide/sulphate ratio with leachability normally increasing with decreasing sulphide/sulphate ratio. The combined results were used to infer the likely behaviour of dredged material upon disposal to land.

Environmental Monitoring↗
PubMed2001

Sorption and desorption behavior of organotin compounds in sediment-pore water systems.

Sediments contaminated with organotin compounds (OTs), in particular triorganotins (TOTs), are abundant in areas with high shipping activities. To assess the possible remobilization of these highly toxic compounds from such sediments, a profound understanding of their sorption/desorption behavior is necessary. In this work the extent and reversibility of sorption of OTs to sediments has been investigated using contaminated freshwater harbor sediments and two certified OT containing marine sediments. Experiments conducted with perdeuterated OTs showed that sorption of OTs to sediments is a fast and reversible process involving primarily particulate organic matter (POM) constituents as sorbents. The organic carbon-normalized sediment-water distribution ratios (DOC, expressed in L/kgOC) determined in the laboratory were consistent with in-situ DOCs obtained from OT concentrations measured in sediment and pore water samples from two dated sediment cores. For both butyl- and phenyltin compounds the log DOC values were in the range of 4.7-6.1, and the following sequence was observed: DOC (tri-OT) > or = DOC (di-OT) > or = DOC (mono-OT). However, the differences were much less pronounced than would have been expected for hydrophobic partitioning of the corresponding compounds into POM. These results support our hypothesis from earlier work with dissolved humic acids that OT sorption to sediments occurs primarily by reversible formation of (innerspere) complexes between the tin atom and carboxylate and phenolate ligands present in POM. Because of the high DOC values (i.e. log DOC > or = 4) the diffusion of OTs from deeper sediments to the surface will be rather slow, and thus a major release from undisturbed sediments is not expected. However, because OTs readily desorb, any resuspension of contaminated sediments (e.g., by the tide, storms or dredging activities) will lead to enhanced OT concentrations in the overlaying water column. Furthermore, in contrastto polycyclic aromatic hydrocarbons (PAH) where large fractions may be tightly bound (in)to soot or other carbonaceous materials, OTs will be more readily bioavailable due to the fast and reversible sorption/desorption behavior.

Absorption↗
PubMed2004

Sorption of phenanthrene to environmental black carbon in sediment with and without organic matter and native sorbates.

Strong sorption to soot- and charcoal-like material (collectively termed black carbon or BC) in soils and sediments is possibly the reason for recent observations of elevated geosorbent-water distribution ratios, slow desorption, limited uptake, and restricted bioremediation. We evaluated the role of environmental BC in the sorption of phenanthrene (PHE) to a polluted lake sediment from a Rhine River sedimentation area. Sorption isotherms were determined over a wide concentration range (0.0005-6 microg/ L) for the original sediment (with organic matter or OM, native sorbates, and BC), sediment from which we had stripped > 90% of the native sorbates (only OM and BC), and sediment combusted at 375 degrees C (only BC). The sorption isotherms of the original and stripped sediments were almost linear (Freundlich coefficient or n(F) > 0.9), whereas the isotherm of the BC remaining after the sediment combustion was highly nonlinear (n(F) = 0.54). At low concentrations (ng/L range), PHE sorption to BC in the combusted sediment was found to exceed the total PHE sorption in the original and stripped sediments. This implies that it may not be possible to use a BC-water sorption coefficient measured in combusted sediment to estimate total sorption to the original sediment. This "intrinsic" BC-water sorption coefficient after combustion was calculated to be 9 times larger than the "environmental" one in the untreated sediment. Competition between the added PHE and the native PAHs and/or OM may explain this difference. It appears that, at low aqueous PHE concentrations (ng/L and below), BC is the most important geosorbent constituent with respect to sorption. At higher concentrations (microg/L), BC sorption sites become saturated and BC sorption is overwhelmed by sorption to the other OM constituents. Because sorption is a central process affecting contaminant behavior and ecotoxicity, understanding this process can strongly contribute to risk assessment and fate modeling.

Adsorption↗
PubMed2005

Microcosm experiments to assess the effects of temperature and microbial activity on polychlorinated biphenyl transport in anaerobic sediment.

Increased polychlorinated biphenyl (PCB) loadings from sediment to the water column under low-flow conditions during late spring and summer months have been observed in the Grasse River (Massena, NY) and other PCB-contaminated rivers in the United States. Temperature appears to be an important factor affecting this phenomenon, as increased sediment temperature leads to increased microbial and bioturbator activity as well as increased rates of diffusion and desorption. Laboratory-scale sediment microcosms were developed and used to study with fine-scale resolution the effects of temperature and microbial activity on PCB transport in river sediment. Over the time course of these experiments, with the extraction procedures used, irreversible sorption of each congener to sediment was observed and increased with aging of the sediment. Temperature-dependent transport was observed for PCB congeners 2,4,5-trichlorobiphenyl (BZ29), 2,5-dichlorobiphenyl (BZ9), and 2-chlorobiphenyl (BZ1) in Grasse River sediment and a synthetic sediment system. The fastesttransport of the congeners occurred in biologically active Grasse River sediment followed by biologically inactive (autoclaved) Grasse River sediment, and synthetic sediment. The increased transport in biologically active sediment demonstrated the importance of microbial activity, in particular gas bubble generation, in PCB transport in near-surface sediments.

Anaerobiosis↗
PubMed2006

Comparative phosphorus sorption by marine sediments and agricultural soils in a tropical environment.

The influence of soil phosphorus (P) sources on P sorption characteristics of marine sediments was investigated for Pearl Harbor and off shore Molokai in Hawaii. Estuary sediments were sampled in seven locations; these represented different soils and on-shore activities. The soil samples included nine major soils that contributed sediment to the Harbor and coastal sediments near the island of Molokai. Sediment and soil samples were equilibrated for 6 days in 0.01 M CaCl(2) solution and synthetic seawater containing differing amounts of P. Phosphorus sorption curves were constructed. The equilibrated solution P, with no P added, ranged from 0.01 to 0.2 mg L(-1); P sorption by sediments at standard solution concentration 0.2 mg L(-1), ranged from 0 to 230 mg kg(-1). Sediment P sorption corresponded closely with soil sorption characteristics. Soils contributing sediments to the west reach of Pearl Harbor are highly weathered Oxisols with high standard P sorption values while those in the southeast of the Harbor were Vertisols and Mollisols which sorb little P. The influence of source materials on sediment P sorption was also observed for off-shore sediments near Molokai. Sediments serve as both source and sink for P in Pearl Harbor and in this role can be a stabilizing influence on P concentration in the water column. Phosphorus sorption curves in conjunction with water quality data can help to understand P dynamics between sediments and the water column and help evaluate concerns about P loading to a water body. For Pearl Harbor, solution P in equilibrium with sediments from the Lochs was 0.021 mg L(-1); a value unlikely to produce an algal bloom. (Measured total P in the water columns (mean) was 0.060.).

Adsorption↗
PubMed2001

Presence of nitrate-accumulating sulfur bacteria and their influence on nitrogen cycling in a shallow coastal marine sediment.

Nitrate flux between sediment and water, nitrate concentration profile at the sediment-water interface, and in situ sediment denitrification activity were measured seasonally at the innermost part of Tokyo Bay, Japan. For the determination of sediment nitrate concentration, undisturbed sediment cores were sectioned into 5-mm depth intervals and each segment was stored frozen at -30 degrees C. The nitrate concentration was determined for the supernatants after centrifuging the frozen and thawed sediments. Nitrate in the uppermost sediment showed a remarkable seasonal change, and its seasonal maximum of up to 400 microM was found in October. The directions of the diffusive nitrate fluxes predicted from the interfacial concentration gradients were out of the sediment throughout the year. In contrast, the directions of the total nitrate fluxes measured by the whole-core incubation were into the sediment at all seasons. This contradiction between directions indicates that a large part of the nitrate pool extracted from the frozen surface sediments is not a pore water constituent, and preliminary examinations demonstrated that the nitrate was contained in the intracellular vacuoles of filamentous sulfur bacteria dwelling on or in the surface sediment. Based on the comparison between in situ sediment denitrification activity and total nitrate flux, it is suggested that intracellular nitrate cannot be directly utilized by sediment denitrification, and the probable fate of the intracellular nitrate is hypothesized to be dissimilatory reduction to ammonium. The presence of nitrate-accumulating sulfur bacteria therefore may lower nature's self-purification capacity (denitrification) and exacerbate eutrophication in shallow coastal marine environments.

Bacteria↗