The chemical phase changes in heavy metals with drying and oxidation of the lake sediments

In order to understand the effects of oxidation on heavy metal behavior in sediments, the changes in chemical phase distributions of heavy metals with oxidation of sediments from Lake Teganuma were investigated using a sequential chemical extraction procedure for heavy metals.The exposure of sediments from the lake bottom to atmosphere caused the increase of Eh and the decrease of acid volatile-S in sediments. Most of the cadmium is expected to exist as relatively stable forms such as sulfides in original reduced sediments prior to exposure to the atmosphere. With the oxidation of sediments, Cd in the sulfidic/organic fraction were transformed to forms in the exchangeable and the reducible fractions which are easily dissolved. The chemical phase changes of Cu, Pb and Zn in sediments were less drastic than the case of Cd. Cadmium distinctly affected by the change in redox potential in sediments, and its behavior in the oxidized state is most mobile. Compared to Cd, the behavior of Cu and Pb are not so remarkably affected by the change in redox condition of sediments.     

Adsorption of trace metals on aluminium oxide: A simulation of processes in freshwater systems by close approximation to natural conditions

The interaction of the trace metals Cu, Co, Zn, Ni, Pb and Cd with aluminium hydroxide precipitated in-situ from homogeneous solution was studied. Using total concentrations of 10⁻⁴ M Al, 10⁻⁷ M Zn, Cu, Co, Ni and 10⁻⁸ M Pb and Cd a removal of Zn, Cu, Pb, Cd from solution occurred together with Al, while Co and Ni concentrations in solution remained unchanged. The binding of Cu, Pb and Zn, Cd is in agreement with the effect predicted by using published (resp. evaluated for Zn and Cd), values for stability constants of surface complexes on preformed Al₂O₃-suspension. The different behaviour of these elements and of Co and Ni is expected from the hydrolysis and adsorption tendencies. The experimental conditions correspond to natural conditions in lake waters, where due to the pH-dependent solubility of aluminium hydroxide, in-situ precipitation may occur and cause the scavenging of trace elements.     

A five-year study on the heavy-metal pollution of Guanabara Bay sediments (Rio de Janeiro, Brazil) and evaluation of the metal bioavailability by means of geochemical speciation

Surface sediments of the Guanabara Bay (Rio de Janeiro, Brazil) were analyzed by a sequential extraction procedure for Cd, Cr, Cu, Pb, Zn, Mn and Fe, determining their distribution among five geochemical phases and in the nitric acid extractable phase. Bioavailable phases and non-bioavailable phases have been determined in six transects in the bay to define the significant level of pollution due to sediment metal contamination. A multiple correlation showed limited responsibility of Mn and Fe oxides and humic acids in the adsorption process, which allowed discrimination among the different processes and suggested the strong influence of the hydrogen sulfide present in the highly reduced bay bottom environment. The authors suggest the need to avoid disturbing bottom sediment by dredging or by artificial bottom aeration which could result in a rapid worsening of the environment due to the accelerated formation of more soluble oxygenated metal compounds making the toxic metals much more available to the benthic fauna and to the bay biota in general.     

Effect of redox potential on heavy metal binding forms in polluted canal sediments in Delft (The Netherlands)

Heavy metal binding forms for Cu, Zn and Pb were determined at four representative sediment sites in the canals of Delft (The Netherlands), using selective chemical extraction methods. Small differences (on average <5%) were found between duplicate extraction experiments. The dominant Cu binding form was always related to sulphide and organics in the sediment. Zn was mainly bound to iron+manganese (hydr)oxides, whereas Pb was rather evenly distributed over the different labile and non-labile binding fractions. A gradual (over about 1 month) increase in redox potentials of the anaerobic sediments led to a 7-37% sediment release of the above heavy metals; this could mainly be ascribed to oxidation of the heavy metal-sulphide bindings. Part of the released heavy metals was re-adsorbed by the labile binding phases ("exchangeable" and "carbonate bound"). Contrary to expectations, we found a decrease rather than an increase in the Fe+Mn (hydr)oxide binding forms. This can probably be ascribed to non-equilibrium reactions in the time span of the experiments, as well as side reactions such as complexation with humic acids and hindered precipitation reactions due to organic matter coatings.     

Seismic bearing capacity of shallow strip foundations in the vicinity of slopes using the lower bound finite element method

The seismic bearing capacity of shallow strip foundations in the vicinity of slopes was investigated by the use of the lower bound limit analysis in conjunction with the finite element method and the linear programming technique. The combination of the most probable failure modes including slope instability and ultimate bearing capacity makes the problem difficult to solve by conventional approximate methods such as the limit equilibrium, the bound theorems of the limit analysis, and the slip line methods since these are based on assumptions about either kinematically admissible failure mechanisms or statically admissible stress fields. The pseudo-static seismic loading scheme was adopted in the presence of both horizontal and vertical acceleration fields, and the soil-foundation interface was assumed perfectly rough. Parametric analyses were conducted to evaluate the most effective factors in the form of the dimensionless strength and geometry parameters. The results of the current study were found comparable with those in the literature, and the consistency of the results confirmed the robustness of the extended finite element lower bound formulation. It was shown that the normalized limit pressure is dramatically reduced as the earthquake acceleration coefficients increases, and that it increases with higher the soil strength parameters. Moreover, the threshold distance at which the influence of the slope diminishes was found to be a function of the soil strength parameters and the slope geometry.     

Heavy metals in the surficial sediments of Fontana Lake, North Carolina

Concern about the possible contamination by heavy metals of Fontana Lake (reservoir) and potential sources of such materials led to a study of surficial sediments. Samples of sediment were collected in the main body of the lake and near the mouths of its major tributaries and analayzed for magnesium, iron, aluminum, manganese, zinc, copper and mercury. Although the drainage area of the reservoir is primarily forested and rural without major industrial developments, the results indicated that manganese, copper and zinc were present in concentrations similar to areas receiving industrial pollution. Chemical analyses of pyritic materials in the watershed (e.g. schists or Anakeesta formation) showed relatively high concentrations of many of the same metals present in Fontana sediments. It appears, therefore, that the metals in the lake sediments represent materials derived from geological sources, although airborne contributions of certain metals cannot be ruled out.     

Experimental and modelling study on the uptake and desorption kinetics of 133Ba by suspended estuarine sediments from southern Spain

Dispersion of pollutants in aquatic environments depends on their uptake by suspended solids. This work deals with the uptake kinetics of 133Ba (gamma-emitter and a good analogue of 226Ra) by suspended estuarine sediments (which can be resuspended into the water column under certain conditions). This study presents a wide set of tracing experiments, including second tracing, decantation and desorption processes. The purpose is to characterize 133Ba uptake by sediments and to investigate the use and limitations of box models in order to describe the uptake kinetics. Water and sediment samples were collected in the Huelva estuary (Spain), where environmental 226Ra concentrations have been increased by two phosphate fertilizer industries. Samples were characterized by granulometric, organic carbon content, cation exchange capacity and XRF-EP analyses. Results revealed three-step kinetics, with characteristic times of minutes, hours and days. These results enabled the selection and calibration of a suitable box model and facilitated the testing of its use as a fully predictive tool.     

Metaux lourds dans les sediments de l'estuaire de la loireHeavy metals in the sediments of the loire estuary

Estuaries, being interfaces between fluviatile and marine environments, are the scene of considerable physico-chemical and biological gradients which can have an effect on the distribution of metallic elements between the solid and dissolved phases. The purpose of the present study was to determine the relative influence of each parameter in this distribution.The study included two series of samples (ICOLO 26 and ICOLO 32) taken by means of the Schipeck grab at 19 selected points of the estuary as indicated in Fig. 1.Within the framework of this study we first investigated and were able to determine the origin and evolution of the metallic elements in the Loire estuary.Pollution levelTable 1 and Fig. 2 summarize the results: firstly, the metallic element contents are relatively low, indicating that pollution is not very strong. Secondly, the contents measured in the different samples vary considerably due to the great heterogeneity of sample composition and particle-size distribution.Upstream-downstream evolutionFigure 2 shows that the longitudinal profiles for metals are very similar to those obtained for the different characteristics of the sediments. Such an observation has already been made by various authors. Owing to the existence of these relationships, we believe, as do Boust et al. (1981), that it is preferable to interpret the results relative to metals obtained on a given site in terms of the various characteristics of the sediment. In Fig. 3, the metallic element contents (ICOLO 26 samples) is thus plotted against organic carbon. As shown in the figure, there is a very good relationship between the two parameters. Figures 2 and 3 indicate that the contents are uniform throughout the estuary with no evidence of further significant sedimentation this uniformity being due to tidal action. Owing to this uniformity, the impact of significant discharges is highly localized except for the wastewater from the city of Nantes as a whole, whose impact which is felt along the entire estuary.The relationship between copper and volatile matter for the ICOLO 32 samples, as represented in Fig. 4, shows that the points fall into two groups, which are the same whatever the explanatory parameter involved. Though the results are more uniform for the ICOLO 26 than for the ICOLO 32 samples, Fig. 6 clearly shows that the “marine” points stand out in both series of samples. This is indicative of a reduction in contents in the downstream direction, especially noticeable beyond point B (Zn, Cr, Ni) or even M (Cd, Cu, Pb).The seasonal evolution is clearly shown on the “metal-characteristic of sediment” graphs by the comparison of the slopes of the lines linking the same point sampled during the two sampling campaigns. The example of copper is shown in Fig. 7.On the whole, analysis of the results derived from the study of one characteristics of the sediment, indicates that only limited enrichment or depletion occurs at a point over a period of time. This probably reflects a good constancy over time of the metallic flux in the estuary. There is little doubt that changes in the composition of the sediment, will cause changes in the trapping of the metallic flux. In this case, variations in contents do not reflect alterations in the metallic flux over the sediment, but the varying capacity of the sediment under investigation to trap the same polluting flux according to is own composition.This study was also productive in the investigation of the various phenomena responsible for the reduction in metal contents during estuarial transit, which phenomenon can be expected to occur in a large number of estuaries.The impact depends on the chemical properties of the element under investigation.Solubilization of metallic elements due to to increased salinity occurs but plays only a secondary role in the upstream-downstream reductions. This is presumably because of the low percentages of metal absorbed in relation to the total amount of metals associated with the sediments.The reduction in metal contents related to the degradation of organic matter also occurs but it is of little significance compared with the overall phenomenon. The disappearance of metals associated with organic matter could well be related to salinity.The considerable reduction of contents in the lower estuary markedly occurs downstream of the salinity front and precisely where the first sediments characteristic of the marine environment are encountered. Consequently, the most obvious parameter responsible for the reduction in the metallic element contents is the mixing of relatively laden fluviatile sediment with “clean” marine sediments.     

Biomonitoring of trace metals in the Black Sea (Romania) using mussels Mytilus galloprovincialis

In a preliminary biomonitoring study, accumulated trace metal concentrations (Cd, Cu, Zn, Hg, Fe, Mn) have been measured in the mussel Mytilus galloprovincialis collected in the Black Sea, at 100 km from the Danube Delta in February 2001 and February 2002. Mussels were collected from four sites. In 2001 metal concentrations were determined in the whole soft body whereas, in 2002, the distribution of metals was evaluated in three different organs (gills, visceral mass and remaining tissues). The results obtained in 2002 confirmed those of 2001. For a given site, concentrations were always higher in the gills and visceral mass of mussels than in the remaining tissues. Principal component analysis allowed separating stations as a function of the metal concentrations in the organs. It is concluded that the mussels M. galloprovincialis are suitable biomonitors to assess changes in metal pollution in this coastal area of the Black Sea.     

The vertical distribution of some heavy metals in three recent sediment cores from the Western Nigerian continental shelf

Results of trace metal analyses of three shallow sediment cores from the Nigerian continental shelf show homogeneities with respect to the vertical distributions of Pb, Ni, Cr and Cu. However, surface enrichment of heavy metals which results from human activities particularly, from Lagos city, is recognised in the uppermost few centimeters in core 12 nearest to the entrance of Lagos harbour. Sediments below this surface enrichment zone, and in the entire lengths of the other two cores which are situated farther east of Lagos port, show heavy metal contents that are more or less constant in vertical distribution with depth.     

Determination and speciation of copper and lead in sediments of a Mediterranean river (River Tenes, Catalonia, Spain)

Total concentrations of Cu and Pb and the speciation of these metals in sediments of the River Tenes are studied in order to establish the extent to which they are polluted and their capacity of remobilization. Five samples taken along the river were analyzed, major components of the sediments were studied using XRF and total Pb and Cu content were determined by AAS. In order to test the accuracy of the digestion methods used (triacid attack with nitric, perchloric and hydrofluoric acids or diacic attack with nitric and hydrochloric acids) for the determination of total trace metal, a standard reference material was also analyzed. Triacid attack is proposed to obtain good results. The results show a highly polluted area (1556 mg kg⁻¹ Cu and 1555 mg kg⁻¹ Pb) in the last sampling site analyzed. For metal speciation, the sequential scheme of Tessier et al. was used. From the results obtained, it can be concluded that Cu content in non-residual fraction is bonded mainly to organic matter, whereas non-residual Pb is mainly associated to iron and manganese oxides.     

Heavy metal contamination in sediments from vehicle washing: a case study of Olarong Chhu Stream and Paa Chhu River,Bhutan

Heavy metal contamination owing to anthropogenic activities affects human health and is of worldwide concern. The aim of the study was to investigate the possible linkage between vehicle washing and heavy metal contamination. Heavy metal concentration in sediment samples from vehicle wash wastewater settlement tanks (WSTs) and water bodies (Olarong Chhu and Paa Chhu) used for discharging untreated wastewater was determined with an atomic absorption spectrophotometer. High concentrations of Cd, Cr, Cu, Fe, Pb, Ni and Zn were found in WSTs. Assessment of sediment pollution in water bodies was determined using contamination factor (CF), pollution load index (PLI), geo-accumulation index (Igeo) and enrichment factor (EF); these indices denoted anthropogenic inputs of heavy metals. Significant Pearson correlations between heavy metals in sediments from Olarong Chhu, Paa Chhu and WSTs indicated their common origin. Thus, this study confirms the linkage between vehicle washing and heavy metal contamination. Bhutan’s policy on installation of wastewater treatment plants should be implemented effectively. Bhutan should consider feasible methods for the safe disposal of sludge from WSTs.

Abbreviations: Atomic Absorption Spectrophotometry - (AAS)     

Effect of untreated urban effluents on the accumulation of toxic metals in river sediments under tropical conditions: Funa River,Kinshasa, Democratic Republic of the Congo

The objective of the present study was to assess the status of surface sediments from Funa River. Sediment samples were characterized for physicochemical parameters, including grain size, organic matter and toxic metals. The result revealed high metal concentrations in river sediments, reaching values of 154.19, 186.00, 1105.34, 3.69, 548.02 and 5.45 mg/kg for Cr, Cu, Zn, Cd, Pb and Hg, respectively. A strong correlation was observed between analysed metals and organic matter suggesting that these contaminants could have originated from common sources with a similar transport pathway. Based on the Sediment Quality Guidelines for the Protection of Aquatic Life, Funa River is considered as highly polluted with toxic metals indicating the potential environmental and human health risk. The results of this research represent a useful tool to assess the sediment quality of urban river receiving system which can be applied to similar environment.     

阴床中混入阳树脂对运行的影响及处理方法

以仪化热电厂出现的阴床中混入阳树脂为例,介绍了所采用的对混床补加新的阳树脂,对水质恶化的阴床更换新的阴树脂,并维修其进水装置、更换损坏的不锈钢绕丝支管等处理方法.从理论上分析了阴床中混入阳树脂对出水水质的不利影响.该厂的经验对同类水处理系统处理此类问题具有一定的指导意义.     

Evaluation of trace metals bioavailability in Japanese river waters using DGT and a chemical equilibrium model

To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water. In this study, we employed the diffusive gradients in thin-films (DGT) to determine the bioavailability of metals (Ni, Cu, Zn, and Pb) in Japanese water systems. The DGT results were compared with a chemical equilibrium model (WHAM 7.0) calculation to examine its robustness and utility to predict dynamic metal speciation. The DGT measurements showed that biologically available fractions of metals in the rivers impacted by mine drainage and metal industries were relatively high compared with those in urban rivers. Comparison between the DGT results and the model calculation indicated good agreement for Zn. The model calculation concentrations for Ni and Cu were higher than the DGT concentrations at most sites. As for Pb, the model calculation depended on whether the precipitated iron(III) hydroxide or precipitated aluminum(III) hydroxide was assumed to have an active surface. Our results suggest that the use of WHAM 7.0 combined with the DGT method can predict bioavailable concentrations of most metals (except for Pb) with reasonable accuracy.     

Speciation and ecological risk of toxic elements in estuarine sediments affected by multiple anthropogenic contributions (Guadiana saltmarshes, SW Iberian Peninsula): I. Surficial sediments

Recent studies have demonstrated that the Guadiana Estuary contains metal concentrations in excess of background values. Therefore, this work aims to document the potential environmental hazards associated with the availability of these metals in this environment of high ecological value. Mineralogical analysis shows that the sediments are composed mainly of quartz, albite, and clay minerals (illite, smectite, kaolinite, and vermiculite) along with several small, reactive compounds (including soluble sulphated salts, Fe-Mn oxyhydroxides, organic matter, and pyrite) capable of retaining metals, which can be subsequently released, causing environmental degradation. BCR sequential extraction shows that As, Cd, Cu, Mn, Pb, and Zn present mobile fractions with respect to the total metal content (41, 100, 57, 53, 70, and 69%, respectively) in any of the described reactive phases (F1 + F2 + F3).Calculated environmental risk indices demonstrate moderate to considerable ecological risk for almost the entire estuary, associated mainly with acid mine drainage from the nearby Iberian Pyrite Belt. In addition, the indices highlight several zones of extremely high risk, which are related to industrial and urban dumps in the vicinity of the estuary and to heavy traffic on the international bridge.     

Partitioning of trace metals between dissolved and particulate phases in a typical backwater system of Kerala,India

Concentrations of dissolved and particulate trace metals (Ni, Pb, Zn and Mn) and their partitioning behaviour between the dissolved and particulate phases in a typical backwater system of Kerala, viz. the southern upstream part of Cochin Estuarine System (South India), have been studied. Spatial and temporal variations of trace metals in the dissolved and particulate phases have been discussed with special reference to pH, dissolved oxygen, salinity and suspended particulate matter. The distribution and partitioning behaviour of trace metals in the water column were found influenced by the presence of a salinity barrier across the backwater system and also by the massive use of pesticides and chemical fertilizers in the vast area of agricultural land near the backwater system. Lack of proper flushing of the backwaters, which receive large amount of trace metals through the application of pesticides and agro‐chemicals, due to the presence of the salinity barrier has significantly affected the water quality of the area.     

The distribution of mercury and other trace metals in the sediments of the Mersey Estuary over 25 years 1974-1998

Mercury and other heavy metals have been monitored in the surface sediments of the Mersey Estuary in NW England for a period of 25 years, using a consistent methodology and sampling grid. This has produced one of the most comprehensive data sets available in the literature and demonstrated some of the difficulties associated with undertaking long-term environmental monitoring. The data indicate that the concentration of mercury and other metals in the sediments of this estuary are strongly correlated to the organic matter and particle size content. This has resulted in the metal distribution patterns reflecting the sediment characteristics and dynamics, irrespective of the position of the input sources. The trend data has indicated a continual, although somewhat uneven, decline in the concentration of most of the metals studied. Remobilisation of previously consolidated saltmarsh sediments can cause significant perturbations in contaminant reduction trends, and needs to be considered in the design of long term monitoring programmes.     

Factors controlling the leaching of major and minor constituents from processed rundle oil shale

The chemical characteristics of leachates from columns of processed oil shale from the Rundle resource, Queensland, were determined and the factors controlling the rate of release of the major and minor constitutents were delineated. The studies were carried out in two types of laboratory columns and a weathering column (lysimeter) exposed to prevailing weather conditions. The flow in the laboratory columns was maintained in an unsaturated mode in order to simulate the flow conditions found in the field.The major constitutents leached from Rundle spent shale are the sulphates and chlorides of Ca, Mg, K and Na. Most of these salts are eluted in the first few pore volumes of leachate. The only major constituents significantly constrained by solubility factors are Ca and SO₄, this being due to solution saturation with respect to gypsum (CaSO₄ · 2H₂O). Chemical equilibria with respect to the ion pairs CaSO₄^o and MgSO₄^o are important in determining the rate of release of Ca, Mg and SO₄.Ion exchange and sorption phenomena are significant in controlling the leaching rate of both the major cationic metal species and the minor (or trace) elements. Many of these minor elements are probably in the anionic form (e.g. As, Se and V), yet are still absorbed by the shale which exhibits no significant anion exchange capacity. Weathering reactions appear to play a significant role in the continued slow leaching of the major and minor species which is observed even after many pore volumes of liquid have eluted.     

Simultaneous multielement determination of trace metals in lake waters by ICP emission spectrometry with preconcentration and their background levels in Japan

An analytical method combining a preconcentration followed by determination with inductively coupled plasma emission spectrometry (ICPES) was developed for monitoring background levels of trace metals in natural waters. Complexes of trace metals (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) and 8-hydroxyquinoline were absorbed to a C₁₈ chemically bonded silica gel disposable plastic column. They were eluted with methanol and digested with nitric acid. With this preconcentration procedure, about 500-fold preconcentration is possible. Simultaneous multielement analysis with ICPES ensures the necessary sensitivity to measure the trace metals in Lake Mashu water at concentration ranges from μg l^?1 (ppb) to ng l^?1 (ppt).Lake Mashu is a deep oligotrophic lake in Hokkaido, Japan and famous for the highest transparency in the world. The trace metal concentrations in Lake Mashu were extremely low: Fe 2.6; Al 1.2; Mn 0.76; Zn 0.63; V 0.15; Cu 0.069; Ti 0.06; Pb 0.05; Ni 0.027; Cd < 0.006; and Co < 0.004 μg l^?1. The suitability of Lake Mashu for a background level monitoring station for global environmental pollution was assessed by the comparison to reference data for other lakes in the world.