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PubMed1999

Ratio of the concentration of anthraquinone to anthracene in coastal marine sediments.

The ratio of the concentration of the oxidation product anthraquinone to that of its parent polycyclic aromatic hydrocarbon anthracene is reported for several coastal marine sediments. The ratio ranges from 0.317 in a highly contaminated industrialized harbor to 2.81 in a remote, less contaminated site. We hypothesize that differences in this ratio result from the input source of PAHs, with input from atmospheric deposition at remote sites resulting in a predominance of anthraquinone (ratio > 1), and direct discharge to highly contaminated industrialized harbors resulting in a predominance of anthracene (ratio < 1). To support this hypothesis, the fate of anthracene in the marine environment was investigated with respect to conversion to its oxidation product, anthraquinone. Once associated with sediments, anthracene is believed to be relatively persistent; however, it can potentially be subjected to oxidation via biological (microbial degradation) and chemical (chemical oxidation and photooxidation) processes. An assessment of the extent of oxidation of anthracene associated with sediments was conducted both under conditions simulating those found in the marine environment and under rigorous conditions by exposure to UV radiation. Results of this study show that while anthracene associated with marine sediments does not readily undergo oxidation to anthraquinone under conditions normally encountered in the marine environment, under extreme conditions anthracene is photooxidized by exposure to UV radiation. The extent of oxidation is influenced by sediment characteristics such as percent organic carbon, humic acid content and sediment surface area. The relative stability of anthracene under normal conditions may help to validate the use of the anthraquinone to anthracene ratio in marine sediments as an environmental marker of contaminant source.

Air Pollution↗

PubMed1999

Cesium-137 and mercury contamination in lake sediments.

The contribution of fluvial discharge and global fallout of 137Cs and mercury to sedimentation fluxes in Lake Shinji and Lake Nakaumi, Japan, was studied. The fluvial flux through soil erosion accounted for 11 to 27% of accumulated 137Cs in the sediments in the 1950's and 1960's, which were the periods of the most extensive atmospheric input, and for 90 to 100% in the 1990's. The vertical profiles of mercury concentrations in the lake sediments studied showed a maximum between 1959 and 1963, which was originated mostly from the extensive use of mercury-agrochemicals in paddyfields of the watershed in the past. These findings are representative examples of long-term contamination of lake sediments caused by the contaminated ground soil erosion.

Cesium Radioisotopes↗

PubMed2001

Impact of frontal systems on estuarine sediment and pollutant dynamics.

In this paper, a brief description of frontal systems, their modes of occurrence and impact on the estuarine environment, is presented. Previous studies of estuarine fronts have largely focused on the water surface and within the water column. New observations in the Tay Estuary, Scotland have shown that the presence of fronts within the water column may be marked, not only by surface foam bands, but also by abrupt (i.e. non-gradational) changes in the underlying bedform morphology and/or sediment facies, as detected using side-scan sonar. This preliminary evidence suggests that fronts may exert a control, not only on the surface and intra-water column sediment and pollutant partitioning, but also on the distribution and persistence of bedload transport pathways.

Animals↗

PubMed2001

Floodplain lakes as sinks for sediment-associated contaminants--a new source of proxy hydrological data?

Lake and reservoir sediments often contain valuable records of sediment yield history and sediment-associated nutrient and contaminant transport spanning timescales from decades to millennia. Nevertheless, there have been few attempts to evaluate floodplain lakes as a source of proxy hydrological data for reconstructing short-term trends in sediment-associated nutrient and contaminant transport. Results from an analysis of floodplain lake sediment cores suggested good preservation of the 137Cs record, which provided an absolute dating control. Changes in the concentration of sediment-associated heavy metals and phosphorus were observed downcore and the analysis of mineral magnetic properties and particle size were used to identify the influx of sediment associated with high magnitude, low frequency flood events. Although floodplain lake-sediments only preserve a partial record, they may provide a valuable source of proxy hydrological data for reconstructing trends in sediment and sediment-associated contaminant transport where long-term sediment monitoring programmes are not available.

Cesium Radioisotopes↗

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

Phenolic xenoestrogens in surface water, sediments, and sewage sludge from Baden-Württemberg, south-west Germany.

Nine structurally different phenolic chemicals, which have been reported to mimic estrogen effects, were determined in various aquatic environmental compartments. Twenty-three water samples from five streams and rivers showed levels up to 458 ng/l for 4-nonylphenol (4NP), 189 ng/l for 4-t-octylphenol (4tOP), 272 ng/l for bisphenol A (BPA) and 47 ng/l for 2-hydroxybiphenyl (2OHBiP). Elevated levels of these compounds in a stream with a high load of effluents of sewage treatment plants (STPs), compared to a brook free of sewage, identified STPs as major sources. With a similar order, 4NP (10-259 micrograms/kg dry matter), 4tOP (< 0.5-8 micrograms/kg), BPA (< 0.5-15 micrograms/kg), and 2OHBiP (2-69 micrograms/kg) were also detected regularly in riverine sediment (n = 11). Levels in sewage sludge were one order of magnitude higher than in sediments. 4-Hydroxybiphenyl and 4-chloro-3-methylphenol were found predominantly in sludge and sediment in the lower ppb range.

Estrogens, Non-Steroidal↗

PubMed2003

Organic compounds and trace metals of anthropogenic origin in sediments from Montego Bay, Jamaica: assessment of sources and distribution pathways.

Surface sediments throughout Montego Bay, Jamaica were collected in 1995 and analyzed for their trace metal and trace organic contaminant content. A variety of trace metals, petroleum hydrocarbons, polycyclic aromatic hydrocarbons, coprostanol as well as chlorinated hydrocarbons such as pesticides and polychlorinated biphenyls were detected and provide evidence for several anthropogenic inputs to the bay. Two main sources of these chemicals are the Montego River and the North Gully, the latter being more significant. Particle-associated pollutants were found to be distributed along the Montego River plume, as well as being transported by the prevailing water currents to the South-Western sections of the bay, probably through re-suspension of enriched fine sediments from the North Gully outfall area.

Environmental Monitoring↗

PubMed2003

Flux estimates and sedimentation of polychlorinated naphthalenes in the northern part of the Baltic Sea.

The concentrations and fluxes of polychlorinated naphthalenes (PCNs) were measured in surface sediments, and settling particulate matter collected in sediment traps, at two coastal and two offshore sampling stations in the Gulf of Bothnia, northern Baltic Sea, Sweden. The PCN concentrations (of tetra- to hepta-chloro congeners) in the surface sediments ranged from 0.27 to 2.8 ng/g dry weight and were of the same order of magnitude as background concentrations reported previously in Europe. The PCN fluxes in the southern basin (0.93 and 0.86 microg/m2/year) of the Gulf of Bothnia were higher than those in the northern basin (0.58 and 0.49 microg/m2/year); they were also higher near the coast than in the open sea. These PCN fluxes are similar to the pre-industrial levels determined from lake sediments in northwest England. The PCN homologue distribution changed from a relatively even distribution in samples collected near the coast, to TeCNs dominating in the samples from the open sea. This indicates that higher chlorinated PCNs are deposited and retained in sediments to a higher degree near the coast. The total annual deposition of PCNs in sediments in the Gulf of Bothnia was estimated to be 91 kg/year.

Geologic Sediments↗

PubMed2002

Release and phase partitioning of metals from anoxic estuarine sediments during periods of simulated resuspension.

Periodically, marine sediments are subjected to physical processes which resuspend them into the water column, releasing previously sequestered metals. The role of resuspension energy and duration on release and subsequent redistribution of sediment bound metals was measured experimentally using a particle entrainment simulator. Two metal contaminated anoxic sediments with different physical and chemical characteristics were resuspended for 12 h at energies of 2 and 5 dynes cm(-2). Samples were taken at specified intervals, and the water column pH, Eh and dissolved oxygen levels were monitored continuously. Over time, metal concentrations increased in the particulate (nonfilterable > or = 1 microm) and filterable (< 1 microm) phases of the overlying water. In general, metal enrichment followed the Irving-Williams order of complex stability. Overall, the sediment's chemical and physical composition were major factors in determining the amount of metal released, more so than the level of resuspension energy applied. These results provide insight into how physical and chemical processes interact during sediment resuspension to release sediment bound metals and control their phase distribution in the water column.

Algorithms↗

PubMed2002

Theoretical considerations on the use of solid-phase microextraction with complex environmental samples.

The equations governing the use of equilibrium solid-phase microextraction (SPME) for environmental samples with complex heterogeneous matrices were derived in terms of parameters commonly measured or estimated by environmental scientists. Parameterization of the SPME equations allowed for the a priori prediction of SPME performance as a function of analyte and sample properties as well as experimental conditions. A theoretical evaluation of SPME was performed for a broad range of realistic scenarios using calculated equilibrium partitioning parameters and the implications for practical applications were discussed. Potential pitfalls and errors in quantitative measurements were identified, and different approaches to SPME calibration were presented. The concept of an optimum minimum volume for the analysis of heterogeneous environmental samples was presented and fully developed. Data from three previous studies were used to validate the correctness of our theoretical framework; the agreement between the measured relative recoveries of a variety of hydrophobic organic chemicals and theoretical predictions was reasonable. The results of this study highlight the potential for SPME to be a valuable technique for the measurement of hydrophobic organic contaminants in complex environmental samples. The SPME technique appears to be especially well suited for samples with high solids-to-water ratios and/or large sample volumes. Examples of such applications include sediment interstitial water and in situ field measurements, respectively.

Calibration↗

PubMed2003

Differential adsorption of molybdate and tetrathiomolybdate on pyrite (FeS2).

Molybdenum is a nutrient important for a variety of biological functions, most notably nitrogen fixation. Molybdenum availability is limited through sorption reactions, particularly in environments rich in sulfide minerals. This study examines the sorption of two major molybdenum species, molybdate (MoO4(2-)) and tetrathiomolybdate (MoS4(2-)), on synthetic pyrite (FeS2) as a function of solution composition. Both MoO4(2-) and MoS4(2-) partitioned strongly on FeS2 under a range of conditions and ionic strengths. Molybdate and tetrathiomolybdate adsorption obeyed a Langmuir isotherm with a calculated site density between 2 and 3 sites/nm2 under acidic and circumneutral conditions, which decreased to less than 1 site/ nm2 at pH 9. Although both MoO4(2-) and MoS4(2-) adsorbed most strongly under moderately acidic conditions, MoO4(2-) readily desorbed while MoS4(2-) remained adsorbed even at high pH. The reversibility of MoO4(2-) adsorption suggests the formation of labile surface complexes while MoS4(2-) likely forms strong inner-sphere complexes. X-ray absorption spectroscopy was used to determine the structure of the surface complexes. Molybdate formed bidentate, mononuclear complexes on FeS2. The Mo-S and Mo-Fe distances for tetrathiomolybdate on pyrite are consistent with the formation of Mo-Fe-S cubane-type clusters. The high affinity of MoS4(2-) for FeS2, as well as its resistance to desorption, supports the hypothesis that thiomolybdate species are the reactive Mo constituents in reduced sediments and may control Mo enrichment in anoxic marine environments.

Adenosine Triphosphatases↗

PubMed2003

Intra-aggregate mass transport-limited bioavailability of polycyclic aromatic hydrocarbons to Mycobacterium strain PC01.

Biodegradation kinetics for three- and four-ring PAHs by Mycobacterium sp. strain PC01 were measured in whole and density-fractionated estuarine sediments and in a system without intra-aggregate mass transport limitations. The biokinetic data in the systems with and without intra-aggregate mass transport limitations were compared with abiotic PAH desorption kinetics. The results indicate that intra-aggregate mass transport limitations, and not the intrinsic bacterial PAH utilization capacity, were most important in controlling the rate of biodegradation of sediment-sorbed PAHs. Achievable extent of biodegradation could be predicted by the independently measured traction of desorbable PAHs in the fast-diffusion regime of a two-domain intra-aggregate mass transport model. A closed-form mathematical model was developed to describe sediment-pore water partitioning and rapid aqueous-phase diffusion of PAHs through the macropore and mesopore network of sediment aggregates, followed by first-order biodegradation of desorbed PAHs in the bulk aqueous domain. The model effectively predicted independent biodegradation kinetics of PAHs field-aged in two estuarine sediments. Despite low aqueous solubility of PAHs, macropore and mesopore diffusion may be an important mechanism controlling intra-aggregate mass transport and bioavailability of the most readily and extensively desorbed PAHs in sediments.

Biodegradation, Environmental↗

PubMed2003

In situ two-dimensional high-resolution profiling of sulfide in sediment interstitial waters.

A recently developed technique of diffusive gradients in thin films (D6T)-computer-imaging densitometry (CID) was improved to study in situ two-dimensional distributions of sulfide in sediment interstitial waters adjacent to the DGT device. The in situ profiler accumulates sulfide from the sediment interstitial water through a diffusive gel onto a AgI binding gel to form black Ag2S. The amount of sulfide bound in the binding gel is then determined from the gray scale density of the dried binding gel. New gel-making procedures were employed to produce stable, evenly dispersed AgI binding gels and to minimize the darkening of the AgI gel upon exposure to light The improved DGT-CID technique was used to profile the distribution of sulfide in sediment interstitial waters at Delta Marsh, a highly productive Prairie wetland on the south shore of Lake Manitoba, at a vertical and lateral resolution of < or = 0.4 mm. The in situ high-resolution microprofiles revealed unprecedented two-dimensional heterogeneity in sulfide concentrations in the sediment interstitial waters adjacent to the DGT device. The mosaic distribution of oxic and sulfidic microenvironments suggested not only the complexity and heterogeneity of the biogeochemistry of sulfur species and sulfide-binding metals (e.g., Cd, Cu, Pb, Hg, Zn) in sediments but also the capability of aquatic organisms for coping with the sulfidic environment

Densitometry↗

PubMed2004

Bioremediation process for sediments contaminated by heavy metals: feasibility study on a pilot scale.

The core stages of a sediment remediation process--the conditioning of dredged sludge by plants and the solid-bed leaching of heavy metals using microbially produced sulfuric acid--were tested on a pilot scale using a highly polluted river sediment. Conditioning was performed in 50 m3 basins at sludge depths of 1.8 m. During one vegetation period the anoxic sludge turned into a soil-like oxic material and became very permeable to water. Reed canary grass (Phalaris arundinacea) was found to be best suited for conditioning. Bioleaching was carried out in an aerated solid-bed reactor of 2000 L working volume using oxic soil-like sediment supplemented with 2% sulfur. When applying conditioned sediment, the oxidation of easily degradable organic matter by heterotrophic microbes increased the temperature up to 50 degrees C in the early leaching phase, which in turn temporarily inhibited the sulfur-oxidizing bacteria. Nevertheless, most of the metal contaminants were leached within 21 days. Zn, Cd, Mn, Co, and Ni were removed by 61-81%, Cu was reduced by 21%, while Cr and Pb were nearly immobile. A cost-effectiveness assessment of the remediation process indicates it to be a suitable treatment for restoring polluted sediments for beneficial use.

Biodegradation, Environmental↗

PubMed2003

Determination of strongly reducing substances in sediment.

Reducing substances in sediments play an important role in regulating the chemical and biological status of the sediment. Strongly reducing substances are the most active part of them, and are difficult to measure directly. In this work, we have developed a method for their determination based on the oxidation by Fe(III). Then, the produced Fe(II) was determined by colorimetry, using 2,2'-bipyridine as the chelating agent. Prior to determination, these substances were extracted from the sediment by M acetic acid. The whole process was carried out in a closed system, so that oxidation of Fe(II) and reducing substances by atmospheric oxygen could be avoided. The calibration curve between absorbance and Fe(II)-chelate concentration in extract was linear. When ascorbic acid was added to the extract, the recovery was larger than 94.0%. The effect of surplus Fe(III) on the result was discussed. With the proposed method, the concentration of strongly reducing substances in sediment samples from Dianchi Lake of China was measured with good reproducibility.

Chelating Agents↗

PubMed2005

Exposure-pathway models explain causality in whole sediment toxicity tests.

Measurements of lethal effect concentrations (LC50) and bioaccumulation following water-only and whole-sediment exposures of the amphipod, Melita plumulosa, and the bivalve, Tellina deltoidalis, to copper, were combined with bioenergetic-based kinetic models of exposure pathways to explain causality in whole-sediment toxicity tests. For both organisms, lethal body concentrations (LBCs) were greater for water-only exposures than for sediment exposures and indicated that the rate of copper accumulation and/or the mode of toxicity of copper assimilated were different for dissolved and particulate phases. The net assimilation of copper, expressed as a lethal exposure concentration (LEC) that was independent of the postexposure copper efflux, was shown to better explain the observed toxicity. The LEC of copper was the same for both water-only and whole-sediment toxicity tests. It is predicted that, for each species, a large range of effect concentrations may be measured for sediments having the same total copper concentration. These are conditional effect concentrations, as their value will be determined by total copper concentrations, partitioning (Kd) relationships (sediment properties), organism physiology (uptake rates from waters, assimilation efficiencies from solids), and organism feeding behavior (feeding selectivity). The importance of these factors to the development of sediment quality guidelines for metals based on species sensitivity distributions is discussed.

Amphipoda↗

PubMed2006

Metal-solid interactions controlling the bioavailability of mercury from sediments to clams and sipunculans.

The bioavailability of sedimentary Hg(II) and methylmercury (MeHg) was quantified by measuring the assimilation efficiency (AE) in the clam Ruditapes philippinarum and the extraction of the gut juices from the sipunculan Sipunculus nudus. Three factors (Hg concentration in sediment, Hg sediment contact time, and organic content of sediments) were modified to examine metal-solid interactions in controlling Hg bioavailability. The Hg AEs in the clams were strongly correlated with the extraction from the sipunculan gut juices for both Hg species. The bioavailability of both Hg(II) and MeHg generally increased with increased sediment Hg concentration but decreased with sedimentmetal contact time and increasing organic content (except that MeHg was not influenced by organic content). Hg(II) speciation in sediments, quantified by sequential chemical extraction (SCE), was dependent on geochemical conditions and greatly controlled the mobility and bioavailability of Hg(II) in sediments. Most bioavailable Hg(II) originated from the strongly complexed phase (e.g., Hg bound up in Fe/Mn oxide, amorphous organosulfur, or mineral lattice), whereas Hg bound with the organocomplexed phase (Hg humic and Hg2Cl2) was not bioavailable. Hg bound with the other geochemical phases (water soluble, HgO, HgSO4, and HgS) contributed very little to the bioavailable Hg due to their low partitionings. Further, the amount of bioavailable Hg was inversely related to the particle reactivity of Hg with the sediments. Detailed analyses of metal-solid interactions provide a better understanding of how Hg in sediments can predict Hg concentration and therefore bioavailability in benthic invertebrates.

Animals↗

PubMed2006

Nitrogen removal in a small constructed wetland: an isotope mass balance approach.

The nitrogen (N) removal potential of constructed wetlands is increasingly used to lower the N load from agricultural nonpoint sources to inland and coastal waters. To determine the removal efficiency and key factors limiting wetland N removal, N fluxes were studied in a small constructed wetland in Central Switzerland. With an isotope mass balance approach integrating the natural isotope signature of nitrate (NO3-, ammonium (NH4+), and particulate nitrogen (PN), the N transformations such as assimilation, mineralization, nitrification, and denitrification were quantified. On average, the wetland removed 45 g m(-2) yr(-1) N during the studied 2.5 years, corresponding to a removal efficiency of 27%. Denitrification contributed 94% to the N removal, while only 6% of the removed N accumulated in the sediments. Denitrification was most efficient during periods with an oxic water column overlying anoxic sediments, as NH4+ released during mineralization of sediment organic matter was completely nitrified and subsequently denitrified at the sediment-water interface. During water column anoxia, NH4+ accumulated in the water and fueled assimilation by duckweed and internal recycling. The NO3-N isotope signature in the wetland mainly reflected the mineralization of sediment organic matter and subsequent nitrification, while denitrification at the sediment-water interface produced no fractionation.

Ammonia↗