Trace Metal Concentrations in Estuarine Sediments PDF Download
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Author: Willem Salomons
Publisher:
ISBN:
Category : Estuarine sediments
Languages : en
Pages : 22
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Book Description
Author: Willem Salomons
Publisher:
ISBN:
Category : Estuarine sediments
Languages : en
Pages : 22
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Book Description
Author: Benjamin Bosschieter
Publisher:
ISBN:
Category : Benthic animals
Languages : en
Pages : 35
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Author: Craig Edward Delphey
Publisher:
ISBN:
Category : Estuarine sediments
Languages : en
Pages : 170
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Book Description
The transfer of trace metals within an estuarine system is a complex function of physical and chemical processes unique to that system. Although interactions of metals with individual components has been studied, there has been little investigation of interactions with multiple component systems. Thus to further understand these processes, an artificial sediment was chosen which would contain the major components of a natural estuarine sediment and would be simple enough to allow the analysis of the quantity of metals within each separate component using a relatively simple extraction technique. In this way metals could be initially dosed on individual sediment components and the redistribution of the metals into other components could be followed as a function of time. The stoichiometry of the metal redistribution could then be studied as well as a general determination made of the rate at which the process could occur. An artificial sediment containing sea water, humic acid, montmorillonite clay, ferrous sulfide, and sand was constructed. Metals were dosed only on one component. The metals chosen were copper, cadmium, lead, and zinc at concentrations of 0.2, 0.1, 0.2, and 0.4 mg/kg in the sediment respectively. The metal-dosed sediments were incubated in plastic bottles over a 44 day period under anaerobic conditions. Bottles were removed periodically for chemical analysis using atomic absorption spectroscopy. Metals associated with each sediment component were stripped by a stepwise extraction procedure devised specifically for this sediment mixture. Pore water was removed by centrifugation, humic acid metals by 1% ammonium hydroide, clay metals with 1% nitric acid, and ferrous sulfide metals by hot concentrated nitric acid. Results indicated that metals transfer occurs rapidly and equilibrium is established within five days. Equilibrium was assumed to exist during Days 5 through 14; concentrations of metals were then computed for each metal component and results were correlated with observations found in natural estuarine sediments. Copper was found associated primarily with ferrous sulfide, while cadmium, lead, and zinc were found with the clay fraction. The distribution was discussed in terms of the affinities of the pure sediment components for the individual metals. Anomalous scattering of data at longer incubation times were explained in terms of buffering changes and carryover of particulate matter. The study concluded that metal transfer between sediment components occurs within a period of several days, that the rate of transfer and stoichiometry were the same for each metal regardless of the initial location, and the extraction technique provided a rapid method of determining the partitioning of metals between the sediment components.
Author: W. Salomons
Publisher:
ISBN:
Category : Diffusion in hydrology
Languages : en
Pages : 80
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Author: W. Baeyens
Publisher: Springer Science & Business Media
ISBN: 9401735735
Category : Science
Languages : en
Pages : 200
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Book Description
Oceans and lakes are characterized by large residence times and can thus be considered as being in an equilibrium or quasi-equilibrium state. In contrast, estuaries, which constitute the interface between the fresh water and marine ecosystems, are biogeochemically and physically very dynamic. Strong gradients in physical and chemical variables such as temperature, pH, salinity, dissolved oxygen, nutrients, amount and composition of particulates result from the mixing of fresh water and saline end members. These gradients provoke increased biogeochemical processes, generally resulting in a geochemical filter (the area of high turbidity, showing enhanced adsorption-desorption processes) and a biological filter (the area of high plankton activity showing, besides a high uptake of nutrients, a high accumulation of trace metals). Both filters disturb the conservative mixing pattern of the trace metals in an estuary. In addition, four aspects make the Scheldt estuary very unusual and different from other estuaries: the Scheldt is a tide-governed estuary which means larger residence times; the upper estuary receives large inputs of biodegradable organic matter which leads to oxygen depletion in winter and to anoxic conditions in summer; inputs of toxic pollutants occur in the upper estuary by the industrial park of Antwerp; the anoxic zone, the zone of pollutant input and the zone of the turbidity maximum coincide geographically. The Scheldt estuary is thus an ideal field laboratory for the study of biogeochemical processes which do not occur elsewhere, or only partially, to a very low extent or in a specific compartment, i.e. the sediments. More specifically, redox processes involving trace metals, the formation of non-labile metal complexes, and the methylation of mercury occur as a result of anoxic conditions and the high load of organic matter. Several models describing in detail the transport, the sedimentation and the speciation of the trace metals in this well-mixed estuary (all major estuaries in EC countries adjacent to the North Sea or the Atlantic Ocean are well-mixed) are presented in this book. A comparison of the metal concentrations over a 15-year period shows a net reduction of the pollution level.
Author: Edward D. Burton
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :
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Abstract: An improved understanding of the geochemical partitioning of trace metals and tributyltin (TBT) in sediments is of great importance in risk assessment and remedial investigation. The aim of this thesis was to examine the distribution and partitioning behaviour of trace metals and TBT in benthic, estuarine sediments. This was achieved by a series of field- and laboratory-based studies investigating factors controlling the geochemical behaviour of trace metals and TBT in sediments from south-east Queensland, Australia. The distribution and enrichment of selected trace metals in benthic sediments of the Southport Broadwater (a semi-enclosed coastal body of water adjacent to the Gold Coast city, south-eastern Queensland, Australia) was studied. Sediment contamination for Cd, Cr, Cu, Ni, Pb, Sn and Zn was assessed by (1) comparison with Australian sediment quality guidelines, (2) calculation of the index of geoaccumulation based on regional background values, and (3) geochemical noi-malisation against Al (i.e. the abundance of alumino-silicate clay minerals). Based on this approach, several sites were found to be strongly enriched with Cu, Pb, Sn and Zn, arising from sources related to either urban runoff or vessel maintenance activities. The geochemical partitioning of Cu, Pb and Zn was examined in sediments collected from three of these sites of sediment contamination. Total Cu, Pb and Zn concentrations in coarse-textured (65 to 90 % sand sized particles), sub-oxic sediments (Eh + 120 to +260 mV) ranged from 8.3 to 194 mg/kg for Cu, 16.3 to 74.8 mg/kg for Pb and 30.1 to 220 mg/kg for Zn, and were related to vertical trends in sediment texture. The association of Cu, Pb and Zn with amorphous oxides, crystalline oxides and organic matter was linearly dependent on the abundance of each phase. For retention by amorphous oxide minerals, the trace metal retention ranged from 5.2 to 23.7 mgcjgFe oxide as Fe for Cu, 1 2.8 to 21 .5 mgpb/gFe oxide as Fe for Pb, and 23. I to 85.7 mgm/gFe oxide as Fe for Zn. Corresponding values for association with crystalline oxides were an order of magnitude less than those for amorphous oxides, indicating a weaker affinity of trace metals for crystalline oxides. The relationships describing association with organic matter ranged from 17.6 to 54.0 mgcu/gorg c for Cu, 6.1 to 9.6 mgpb/gorg c for Pb and 6.4 to 16.4 mgzn/gorg c for Zn. The in-situ solid/pore-water partitioning of TBT and the degradation products, dibutyltin (DBT) and monobutyltin (MBT), was determined for an estuarine sediment profile with previously identified elevated Sn concentrations. Total butyltin levels were (depending on depth) 220 to 8750 jig/kg for TBT, 150 to 5450 jig/kg for DBT and 130 to 4250 jig/kg for MBT. Pore-water butyltin concentrations ranged from 0.05 to 2.35 jig/L for TBT, 0.07 to 3.25 jiglL for DBT, and 0.05 to 0.53 J.tgIL for MBT. The organic carbon normalised distribution ratios (Doc) were similar for TBT, DBT and MBT, and were io to 106 L/kg. Values for the Butyltin Degradation Index (BDI) were larger than I at depths greater than 10 cm below the sediment/water-column interface, indicating that substantial TBT degradation has occurred in the sediments. This suggests that natural attenuation may be a viable sediment remediation strategy. Factors controlling the partitioning behaviour of Cu, Pb and Zn in nonsulfidic, estuarine sediments were examined in controlled laboratory-based studies with the use of combined sorption curve - sequential extraction analysis. This allowed determination of sorption parameters for Cu, Pb and Zn partitioning to individual geochemical fractions. Partitioning behaviour in sulfidic sediments was also determined by sequentially extracting Cu, Pb and Zn from synthetic sulfide minerals, and from natural sediment and pure quartz sand after spiking with acid-volatile sulfide (AVS). Trace metal sorption to the 'carbonate' fraction (pH 5, NaOAc extraction) increased with metal loading due to saturation of sorption sites associated with the 'Fe-oxide' (NH2OH. HCI extraction) and 'organic' (H202 extraction) fractions in non-sulfidic sediments. Freundlich isotherm parameters describing sorption to the 'Fe-oxide' and 'organic' fractions were dependent on the sediment Fe-oxide and organic carbon content, respectively. Sequential extraction of Cu from pure CuS, AVS-spiked sediment and AVS-spiked quartz sand showed that AVS-bound Cu was quantitatively recovered in association with the 'organic' fraction. However, some AVS-bound Pb and Zn were recovered by the NH2OH. HCI step (which has been previously interpreted as 'Fe-oxide' bound metals) in the sequential extraction procedure used in this study. This indicates that the sequential extraction of Pb and Zn in sulfidic sediments may lead to AVS-bound metals being mistaken as Fe-oxide bound species. Caution should therefore be exercised when interpreting sequential extraction results for Pb and Zn in anoxic sediments. Tributyltin (TBT) sorption to four natural sediment samples in artificial seawater was also examined under a range of modified pH and salinity conditions in controlled laboratory-based studies. Three of the sediment samples were relatively pristine with regard to TBT contamination, but the fourth was a TBT-contaminated sediment from a commercial marina. Sorption of TBT was described well by linear sorption isotherms, with distribution coefficients ranging from 6.1 to 5210 L/kg depending on pH and salinity. Sediment organic C content and particle size distribution were important determinants of sorption behaviour. The presence of resident TBT in the contaminated marina sediment caused a substantial reduction in TBT sorption due to satuaration of high selectivity sites. Desorption of TBT from the marina sediment was described by relatively large observed distribution coefficients ranging from 5100 to 9400 L/kg, suggesting that aging effects may reduce sorption reversibility. Increased artificial seawater salinity generally reduced TBT sorption at pH 4 and pH 6, but enhanced TBT sorption at pH 8. Regardless of salinity, maximum sorption of TBT was observed at pH 6, which is attributed to an optimal balance between abundance of the cationic TBT species and deprotonated surface ligands. Consideration of aqueous TBT speciation along with octanol-water partitioning behaviour suggest that hydrophobic partitioning of TBTCI to non-polar organic matter was important for pH (up to) 6, whilst partitioning of TBTOH was important at higher pH. The effect of aging on the solid/pore-water partitioning and desorption behaviour of TBT in sediments was examined. Three sediment samples with contrasting physical and chemical properties were spiked with 10 mg/kg TBT and aged under sterile conditions for periods of time ranging from I to 84 days. Aging had a negligible effect in a sandy sample with very low organic carbon content (0.2 % w/w). In contrast, for samples with larger amounts of organic carbon (2.6 and 4.8 % w/w), the effect of aging on the solid/pore-water partitioning behaviour was significant. For these samples, the apparent distribution coefficients (Ks) obtained from sequential two hour desorption experiments exhibited a two-fold increase between spiked sediments subjected to aging for 1 day and 84 days. This study demonstrates that aging effects may be an important aspect of TBT fate in contaminated sediments. Overall, the results described in this thesis demonstrate that environmental factors (i.e. pH, salinity, Eh, aging) and sediment composition (i.e. abundance of fine alumino-silicate minerals, organic matter, Fe-oxides, reactive sulfides) exert substantial effects on trace metal and TBT partitioning. The current reliance on measurement of total trace metal and TBT concentrations in contaminated sediment management may consequently lead to inaccurate estimates of environmental risk and inappropriate remediation measures if other factors regulating contaminant distribution and partitioning are ignored.
Author: Harry James Simpson
Publisher:
ISBN:
Category : Dredging
Languages : en
Pages : 228
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Author: Jeffrey S. Levinton
Publisher: Cambridge University Press
ISBN: 9780521844789
Category : History
Languages : en
Pages : 514
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Book Description
The Hudson River Estuary, first published in 2006, is a scientific biography with relevance to similar natural systems.
Author: Raurrie Patrick Johnson
Publisher:
ISBN:
Category : Estuarine sediments
Languages : en
Pages : 48
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Author: Robert J. Davies-Colley
Publisher:
ISBN:
Category : Estuarine sediments
Languages : en
Pages : 224
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Sediments are the major compartment in aquatic environments for many materials of toxic or nutrient concern. The lack of knowledge of the phase associations of toxic metals in sediments is the largest deficiency in our understanding of the environmental hazard posed by metal contamination. This study examined the sedimentary partitioning of copper and cadmium with the goal of predicting the environmental fate of these metals in estuaries. Five solid phases: synthetic hydrous oxides of iron and manganese, montmorillonite clay, a synthetic aluminosilicate gel, and estuarine humic substances (EHS) extracted from a natural sediment were chosen to simulate components responsible for trace metal binding in oxidized sediments. The uptake of copper and cadmium by these model phases in artificial seawater was measured as a function of pH and salinity. Affinity of the model phases for cadmium as measured by K[subscript p], the slope of the linear adsorption isotherm, was in the following order: manganese> iron> EHS> aluminosilicates> montmorillonite. Copper binding affinities were much higher than those of cadmium but the relative order of affinity of the phases was similar except for copper binding by EHS for which K[subscript p] was relatively higher (exceeding that of iron). Metal binding was not influenced by interactions involved in three types of phase complex: iron-clay, iron-humic and clay-iron-humic suggesting that experiments with isolated phases are adequate to predict partitioning. The measured K[subscript p] values were used to calibrate a simple model for predicting partitioning and total metal uptake by sediments. This model which is analogous to speciation in a solution of competing ligands, predicts that cadmium uptake by estuarine sediments is dominated by iron while both iron and organics are important for copper. Results of selective extraction studies and studies of cadmium uptake by natural estuarine sediments are in semiquantitative agreement with these predictions. In anaerobic sediments thermodynamic calculations suggest that copper and cadmium concentrations are determined by equilibria involving solid sulphides and bisulphide and polysulphide complexes. It is expected that the results of this investigation will aid in assessing the environmental significance of metal-contaminated estuaries.
