PubMed Health⌕ Search

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 1,243 records · Page 69Linked to original sources
PubMed2005

Ecological risk assessment of polycyclic aromatic hydrocarbons in sediments: identifying sources and ecological hazard.

Polycyclic aromatic hyftovst ond (PAH) are nearly ubiqutous contaminants of freshwater and marine sediments. Sediment PAHs are derived from combustion of organic matter, fossil fuels, and biosynthesis by microbes. Pyrogenic PAHs, particularly those associated with combustion particles (soot), have a low accessibility and bioavailability in sediments. Polycyclic aromatic hydrocarbons associated with petroleum, creosote, or coal tar in sediments may have a moderate accessibility/bioavailability, particularly if the PAHs are part of a nonaqueous phase liquid (NAPL) phase that is in contact with sediment pore water. We present a method for estimating the hazard of complex PAH assemblage in sediments to benthic organisms. Concentrations of all PAHs in sediment pore water are estimated by an equilibrium partitioning model relative to concentrations in bulk sediment. Predicted log Koc values can be used for predicting sediment/water partitioning of petrogenic PAH, but empirically derived log Kd values are needed to predict partitioning of pyrogenic PAH. A hazard quotient (HQ) for each PAH is calculated as the ratio of the estimated concentration in pore water to the chronic toxicity of the PAH determined by a log Kow/toxicity model. Hazard quotients for all PAH in a sample are summed to produce a hazard index (HI), which is a measure of the worst-case estimated hazard of the sediment PAH to benthic organisms. The results of this study show that the integration of HI results with PAH source data provides insights into the causes of sediment toxicity that are useful in an ecological risk assessment.

Animals↗
PubMedDate not supplied

Accumulation, release, and solubility of arsenic, molybdenum, and vanadium in wetland sediments.

This study was undertaken to determine the fate of As, Mo, and V (trace elements, TEs) in the sediments of a constructed wetland in use for the remediation of potentially toxic trace element-contaminated agricultural drainwater. After three years of wetland operation, sediment cores were collected to determine changes in TE concentrations as a function of depth and the effects of varying water column depth. All TE concentrations were highest in the top 2 to 4 cm and decreased with depth. Molybdenum accumulated in the wetland sediments, up to levels of 32.5 +/- 4.6, 30.2 +/- 8.9, and 59.3 +/- 26.1 mg kg(-1) in the top 1 cm of sediment at water depths of 15, 30, and 60 cm, respectively. In the top 2 cm of sediment, As accumulated (28.2 +/- 3.0 mg kg(-1)) only at the 60-cm water depth. Below 2 cm, as much as 10 mg kg(-1) of As was lost from the sediment at all water depths. In most cases, V concentrations decreased in the sediment. In this wetland system, the lowest redox potentials were found near the sediment surface and increased with depth. Thus, in general As, Mo, and V concentrations in the sediment were highest under more reducing conditions and lowest under more oxidizing conditions. Most of the accumulated Mo (73%) became water soluble on drying of samples. This has important implications for systems undergoing changes in redox status; for instance, if these wetland sediments are dried, potentially large amounts of Mo may be solubilized.

Arsenic↗
PubMedDate not supplied

Effects of sedimentation on soil nutrient dynamics in riparian forests.

The influence of sedimentation rates on biogeochemistry of riparian forests was studied near ephemeral streams at Fort Benning, GA. Upper reaches of seven ephemeral streams had received varying rates of sedimentation stemming from erosion along unpaved roadways at the military installation. Two reference catchments were also included in the study. Decomposition of foliar litter, microbial C and N, N mineralization, and arthropod populations were compared within and among catchments. Rates of sedimentation over the past 25 yr ranged from 0 in references to 4.0 cm yr(-1). Decomposition rates declined exponentially with sedimentation rates as low as 0.20 to 0.32 cm yr(-1) and appeared to reach an equilibrium at a sedimentation rate of 0.5 cm yr(-1). Nitrogen mineralization and microbial C and N followed the same trend. Sedimentation had no discernible effect on arthropod populations. These data suggest that biogeochemical cycles may be altered by sedimentation rates that commonly occur in some floodplain forests.

Animals↗
PubMed2001

Impact of sediment manipulation on the bioaccumulation of polycyclic aromatic hydrocarbons from field-contaminated and laboratory-dosed sediments by an oligochaete.

The accumulation kinetics of polycyclic aromatic hydrocarbons (PAHs) by the freshwater oligochaete Lumbriculus variegatus were measured for field-contaminated and laboratory-dosed sediment. In addition, sediment manipulations typically used for homogenization and dosing in bioaccumulation assays were compared. Rather than an asymptotic approach to steady state, both resident and dosed PAH accumulation exhibited a peak during the 14-d assays, with steeper declines being noted for the lower-molecular-weight compounds. Lack of evidence of a peak for higher-molecular-weight PAHs may be due to slower kinetics and the short length of the assay. Relative to minimally mixed sediment, slurried sediment enhanced the accumulation of less-soluble resident PAHs, did not affect moderately soluble PAHs, and reduced the uptake of the more-soluble PAHs, fluorene and phenanthrene. Aging sediment after mixing reduced the availability of highly to moderately soluble resident PAHs but had no effect on less-soluble PAHs. A similar effect was noted for dosed PAHs, though a larger reduction in bioavailability was observed. Dosed PAH uptake clearance coefficients (ks) exceeded those of minimally mixed resident PAHs by factors of 3 to 4 for pyrene and 26 for benzo[a]pyrene. These results demonstrate that sediment manipulations and contamination history need to be considered when measuring PAH bioaccumulation.

Animals↗
PubMed2002

Polychlorinated dibenzo-p-dioxins and dibenzofurans and dioxinlike polychlorinated biphenyls in sediments and mussels at three sites in the lower Great Lakes, North America.

Levels of contaminants including polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), non-ortho-substituted and mono-ortho-substituted dioxinlike polychlorinated biphenyls (DLPCBs) were determined in sediments and freshwater mussels (Dreissena spp. and Elliptio complanata) at three sites in the lower Great Lakes (North America). Impacts of mussel colonization on sediment quality were investigated by comparing contaminant levels in colonized sediment with levels in sediment in the same area that was not colonized, but exposed to similar environmental conditions. Significant impacts on contaminant levels of colonized sediment, compared to noncolonized sediment, were observed at two sites exhibiting high mussel population densities (Fort Erie, eastern Lake Erie, ON, Canada, 2.2 kg/m2 dry wt biomass, and Port Dalhousie, western Lake Ontario, Ontario, Canada, 6.1 kg/m2 dry wt biomass); these differences were not observed at a site with lower mussel densities (Bay of Quinte, eastern Lake Ontario, Ontario, Canada, 0.7 kg/m2). Total organic carbon and contaminant concentrations were statistically significantly greater in colonized sediment, compared to noncolonized sediment, at the two impacted sites. Areal estimates of PCDD/PCDF and DLPCB toxicity equivalents (TEQs) in mussel biomass at the three sites averaged 0.16% and 3.3%, respectively, of the TEQs in the top 3 cm of sediment, indicating that the sediments were the primary sink for contaminants. The observed differences between colonized and noncolonized sediment suggest that Dreissena are capable of influencing the chemical properties of sediment they colonize.

Animals↗
PubMed2002

Predicting amphipod toxicity from sediment chemistry using logistic regression models.

Individual chemical logistic regression models were developed for 37 chemicals of potential concern in contaminated sediments to predict the probability of toxicity, based on the standard 10-d survival test for the marine amphipods Ampelisca abdita and Rhepoxynius abronius. These models were derived from a large database of matching sediment chemistry and toxicity data, which includes contaminant gradients from a variety of habitats in coastal North America. Chemical concentrations corresponding to a 20, 50, and 80% probability of observing sediment toxicity (T20, T50, and T80 values) were calculated to illustrate the potential for deriving application-specific sediment effect concentrations and to provide probability ranges for evaluating the reliability of the models. The individual chemical regression models were combined into a single model, using either the maximum (P(Max) model) or average (P(Avg) model) probability predicted from the chemicals analyzed in a sample, to estimate the probability of toxicity for a sample. The average predicted probability of toxicity (from the P(Max) model) within probability quartiles closely matched the incidence of toxicity within the same ranges, demonstrating the overall reliability of the P(Max) model for the database that was used to derive the model. The magnitude of the toxic effect (decreased survival) in the amphipod test increased as the predicted probability of toxicity increased. Users have a number of options for applying the logistic models, including estimating the probability of observing acute toxicity to estuarine and marine amphipods in 10-d toxicity tests at any given chemical concentration or estimating the chemical concentrations that correspond to specific probabilities of observing sediment toxicity.

Amphipoda↗
PubMed2002

Use of triolein-semipermeable membrane devices to assess the bioconcentration and sediment sorption of hydrophobic organic contaminants in the Huaihe River, China.

Triolein-containing semipermeable membrane devices (triolein-SPMD) were deployed I m above the sediments at two sampling sites in the Huaihe River, China, for a period of 28 d. Sediment and fish samples were simultaneously collected from the same sampling sites. Concentrations of substituted benzenes, selected pesticides, polycyclic aromatic hydrocarbon (PAH), and polychlorinated biphenyls (PCBs) were measured in triolein-SPMDs, sediments, and fishes. The concentrations of these hydrophobic organic contaminants (HOCs) in fish and in sediment organic carbon were correlated with HOCs accumulation in triolein-SPMDs. Our results showed reasonably good correlations between the log concentrations of contaminants in fish lipid and in triolein-SPMDs. Good correlations were also found between the log concentrations of contaminants in sediment organic carbon and in triolein-SPMDs (except for PAHs). The results were discussed in terms of the partitioning of hydrophobic organic contaminants among different compartments in the aquatic environment and the suitability of using triolein-SPMDs to predict bioconcentration factor (BCF) and sediment-water partitioning coefficient (K(oc)).

Adsorption↗
PubMed2003

[Organochlorine residues of sediments in Taihu Lake and its risk evaluation].

This study analyzed chlorinated pesticides of sediments in Taihu Lake. The DDT, DDE, DDD, HCH isomers, Aldrin, Diddrin, Hexachlorobenze, Heptachlor were measured in all samples. beta-HCH, p, p'-DDE and Hexachlorobenze had higher concentrations than others. The average values of them were 6.572 ng/g, 1.432 ng/g and 2.158 ng/g, respectively. HCHs in sediments were higher than DDTs. The organochlorine residues in sediments mainly originated form the runoff, atmospherically deposition and industrial sewage. HCHs and DDTs of sediments in Taihu Lake were higher than those of sediments in Chinese rivers, but lower than those of bays reported in some papers. According to the ERL and ERM value of risk evaluation for ocean which can also be applied for lake, sediments in Taihu Lake pose a low risk to consumers of bottom feeders.

China↗
PubMed2003

[Sediment chlorophyll in HAB (harmful Algal bloom) area of East China Sea].

The content and distribution of chlorophyll a (chl-a) and phaeopigments (pha-a) in the sediment of East China Sea was investigated in August and September, 2002. The results showed that chlorophyll a and phaeopigments had the same resource. Both chlorophyll a and phaeopigments decreased significantly with increasing depth, and would be stable to a certain depth. There are several observed leaps in the vertical distribution of chlorophyll a and phaeopigments, which might reflect the effects of bioturbation. The chlorophyll a and phaeopigments concentration on the surface of sediment varied from 0.14 to 1.17 micrograms.g-1 and 0.83 to 5.58 micrograms.g-1, respectively, and the mean concentrations in the top centimeter of sediment (0-0.5 cm) were 0.54 microgram.g-1 for chlorophyll a and 2. 45 micrograms.g-1 for phaeopigments. The spatial distribution of benthic chlorophyll a and phaeopigments were affected by the combination of several factors such as depth (and therefore light), temperature, salinity and water content. As the main degradation product of chlorophyll a, phaeopigments became the main type of chlorophyll while increased to certain extent, and accounting for 80-90% of total chlorophyll. Due to the water temperature, the surface chlorophyll a and phaeopigments concentration varied significantly with the season. Total chlorophyll a in the sediment accounted for 31% of total chlorophyll a in the water column.

China↗
PubMed2005

Abundances, depositional fluxes, and homologue patterns of polychlorinated biphenyls in dated sediment cores from the Pearl River Delta, China.

Despite the recent efforts to investigate the distribution and fate of persistent organic pollutants in the tropical and subtropical regions of Asia, very little was known about the temporal change of polychlorinated biphenyls (PCBs) in the environmental ecosystem of China. In this study, three dated sediment cores collected from the Pearl River Delta of southern China were analyzed for a large suite of PCB congeners, from which the temporal profiles of PCB abundances, fluxes, and homologue patterns were constructed. The sedimentary inventories of total PCBs at the sampling sites ranged from 480 to 1310 ng/cm2, at the low end of the worldwide figures. Although production and use of PCBs have been banned or highly restricted in China since the early 1980s, the fluxes of total PCBs continued to increase in the Pearl River Delta sediments. There was a concurrent increase of PCB fluxes and gross domestic product per capita in the region from 1980 to 1997, and a decline of agricultural land use was evident at the same time. Apparently, large-scale land transform since the early 1980s as well as emissions from the PCB-containing electrical equipments were responsible for the sharp rise of PCB fluxes in the recent sediments. The difference in the PCB homologue patterns from 1940 to the mid-1970s was probably indicative of the different timelines of PCB usage in Macao/Hong Kong and mainland China and the differenttypes of technical PCBs commercially used. PCBs were detectable in sediments deposited well before the time frame when production of PCBs began (before 1930) and were relatively enriched in the less chlorinated homologue groups (3Cl and 4Cl PCBs), suggesting the downward mobility of lightly chlorinated PCB congeners in the sediment column.

China↗
PubMed2005

[Characteristics and effect factors for sorption of trichlorobenzene on sediment in Huaihe River (Jiangsu reach)].

The characteristics for sorption of trichlorobenzene on sediment in Huaihe River (Jiangsu reach) was studied. It was also in vestigated at the same time that some factors of influence on the sorption, such as initial consistence of adsorbate, concentration of adsorbent and pH value, by ortho-experiment. The results indicate that the sorption isotherms of trichlorobenzene to sediment in Huaihe River (Jiangsu reach) are linear in the experiments condition,and distribution plays a leading role. The affected degrees of different environmental factors are different for sorption of trichlorobenzene on sediment in Huaihe River. The results of ortho-experiment are analysis with SPSS(Statistical Package for the Social Science) and the results are indicate that the affection of initial consistence of adsorbate is the biggest in all environmental factors,and initial consistences of adsorbate have expressly significant influence for sorption of trichlorobenzene on sediment in fresh water, and yet the pH has almost no influence for the sorption of trichlorobenzene on same sediment.

Adsorption↗
PubMed2006

[Determination of methylmercury in biological and sediment samples by capillary gas chromatography on-line coupled with atomic fluorescence spectrometry].

A comprehensive method for the determination of methylmercury by capillary gas chromatography (GC) on-line coupled with atomic fluorescence spectrometry (AFS) was developed. The hyphenation system was carefully designed and the operation conditions such as injector temperature, carrier gas flow rate, make-up gas flow rate and argon flow rate were optimized in detail. The absolute detection limits (3sigma) were 0.005 ng of Hg for both methylmercury (MMC) and ethylmercury (EMC). The relative standard deviations (RSD, n = 5) for MMC and EMC at 10 ng x mL(-1) of Hg levels were 2.5% and 1.3%, respectively. The method was evaluated by analyzing a certified reference material (DORM-2), and the MMC concentration determined was in good agreement with the certified value. In addition, the recoveries of MMC in two sediment samples were 70% and 77%, respectively. The proposed method was accurate, sensitive and suitable for the determination of MMC in biological and sediment samples.

Animals↗
PubMed2002

Cyst-based toxicity tests XII--development of a short chronic sediment toxicity test with the ostracod crustacean Heterocypris incongruens: selection of test parameters.

Experiments were carried out with neonates of the freshwater ostracod Heterocypris incongruens hatched from cysts in order to develop a new culture/maintenance-free solid-phase microbiotest for the toxicity assessment of contaminated sediments. Based on preliminary investigations, a number of test parameters were investigated for a short-chronic assay: hatching time, size of the cups of the multiwell test plates, feeding of the test organisms prior to the test, amount of supplemental algal food, volume of sediment, and duration of the test. On the basis of the findings, a test protocol was formulated for a 6-day assay in 12-cup multiwell plates with 10 organisms per cup and 3 replicates. The test organisms were collected 52 h after the start of the incubation of the cysts in standard freshwater at 25 degrees C under continuous illumination after a 4-h prefeeding with 1.3 mg/mL Spirulina. The test biota in the cups were exposed to 300 microL of test sediment in 2 mL of standard freshwater with 3 x 10(7) live algal cells (Raphidocelis subcapitata) as food supplement. Calibrated sand was used as a reference sediment. Mortality and growth of the ostracods were determined after 6 days' incubation at 25 degrees C in darkness. The selected test parameters for the new microbiotest were found adequate for toxicity determination of natural sediments compared with the 10-day contact test with the amphipod Hyalella azteca.

Animals↗
PubMed2003

Analysis of pesticides in water and sediment under different storage conditions using gas chromatography.

This paper describes the process of testing a simple low-solvent method for simultaneously extracting five classes of pesticides (triazines, organophosphates, organochlorines, pyrethroids, and carbamates) from reconstituted water and sediment. This method uses techniques available in most laboratories, namely solid phase extraction (SPE) and sonication in combination with gas chromatography. The recoveries of pesticides ranged from 60 to 120% with the exception of carbaryl, dicofol, and methoxychlor that had higher recoveries. Methods were further tested with pond water and soil samples. The recoveries of pesticides from soil were comparable with those from sediments, while in pond water, recoveries of the organochlorines exceeded 100%. A matrix enhancement effect was suspected to be the cause for the observed elevated recoveries. In order to determine time range and conditions in which the samples can be stored without significant losses, recoveries of pesticides in water and sediment were monitored for 28 days. Water samples were most stable when extracted immediately and stored in SPEs in the freezer. These samples remained stable for up to six weeks in the freezer, whereas sediment samples were stored for a month without a significant decrease in pesticide concentrations.

Chromatography, Gas↗
PubMed2000

Bacterial reduction of copper-contaminated ferric oxide: copper toxicity and the interaction between fermentative and iron-reducing bacteria.

Fe(III) oxide is an important heavy-metal sink, and bacteria are responsible for much of the Fe(III) reduced in nonsulfidogenic aquatic environments, yet factors governing the bacterial reduction of heavy metal-contaminated iron oxide are largely unknown. In this study with a stabilized bacterial consortium enriched from metal-contaminated sediments, we demonstrate that Cu toxicity impedes anaerobic carbon oxidation and bacterial reduction of hydrous ferric oxide (HFO). In the enrichment culture, a Clostridium sp. fermented lactate to propionate and acetate and Fe(III) reducers coupled acetate oxidation to HFO reduction. Increasing the amount of Cu in the culture medium significantly extended the time before Fe(III) reduction occurred and decreased the reduction rate, but did not affect the extent of HFO reduction. The Clostridium had a higher Cu-complexation capacity than the Fe(III) reducer Shewanella alga. Iron reduction was inhibited until almost all of the dissolved Cu was removed from solution and occurred two to seven times faster if the sediment enrichment culture was fed lactate instead of acetate. Our findings suggest that fermentative bacteria play a role in ameliorating heavy metal toxicity to iron-reducing bacteria. Fermenters may therefore enhance metal release in sediments by facilitating the bacterial reductive dissolution of heavy metal-contaminated HFO.

Bacteria↗