Academic literature on the topic 'Metal contaminated sediments'

Abstract. Total metal concentrations in surface sediments and historically contaminated sediments were determined in sediment cores collected from three estuaries (Thames, Medway and Blackwater) in south-east England. The partitioning behaviour of metals in these sediments was also determined using a sequential extraction scheme. These data were then compared with sediment quality values (SQVs) to determine the potential ecotoxicological risk to sediment dwelling organisms. When total metal concentrations in surface sediments are examined, no risk to biota in any of the estuaries is indicated. However, when historically contaminated sediments at depth are also considered, risks to biota are apparent and are greatest for the Thames, followed by the Medway and then the Blackwater. This suggests that regulatory authorities should examine vertical metal profiles, particularly in estuaries that are experiencing low sediment accumulation rates where historically contaminated sediments are in the shallow sub-surface zone and where erosion or dredging activities may take place. When metal partitioning characteristics are also considered, the risk to biota is comparable for the Medway and the Blackwater with the potentially bioavailable fraction presenting no ecotoxicological risk. Conversely, over 70% of metals are labile in the Thames Estuary sediments and toxic effects are probable. This suggests that the application of SQVs using total sediment metal concentrations may over- or under-estimate the risk to biota in geochemically dissimilar estuarine sediments. Keywords: sediment quality values, estuarine sediments, metal contamination, partitioning, sequential extraction

Stormwater runoff has resulted in heavy metal contamination throughout much of the Port Jackson estuary, Sydney, Australia. Metal partitioning was investigated in the benthic estuarine sediments of Iron Cove, an off-channel embayment of Port Jackson. Contamination was greatest near the stormwater canal, where sediments were anoxic and contained high concentrations of sulfide in the porewater. Away from the canal a layer of non-cohesive, sub-oxic surficial sediment containing high dissolved iron was found overlaying a more cohesive substratum. At all sites, porewater Cd, Cu, Ni, Pb and Zn were <2.5 g L–1, and negligible metal release was observed upon sediment resuspension. According to water quality guidelines, the ecological risk posed by dissolved metals from the Iron Cove sediments is low. Estimated fluxes of Cd, Cu, Ni, Pb and Zn from the sediments were calculated to be <0.2 mol m–2 day–1. The rapid oxidation then hydrolysis of iron(II) in porewaters caused a drop in pH and the formation of iron hydroxide precipitate. These processes may affect dissolved metal concentrations; hence, oxidation of samples must be avoided during sampling and extraction procedures. Sediment-bound zinc was the metal most easily mobilized.

The contamination of sediments with heavy metals may lead to serious environmental problems and in some cases action has to take place for their decontamination. In this work, studies were performed on sediments near the outfall of domestic and industrial waste. The metals examined were Cu, Cr, Ni, Pb, Zn and Fe. Indeed, high metal content was found in the sediments and the contamination factors were quite high, indicating the effect of the nearby discharge of effluents. The results of the application of a sequential extraction partitioning procedure indicated that an important part of the metal content is carried by the residual phase but also a significant percentage is found in the organic and reducible fractions, i.e. in potentially available fractions. Batch extraction experiments using acid solutions of various concentrations and different acid-sediment contact times were performed in order to remove heavy metals from the sediments. For most metals studied, a satisfactory percentage was extracted at low contact times.

The behaviour of heavy metals has been investigated in contaminated sediments of the river Meuse, The Netherlands. Due to temporal changes in temperature and degradability of organic matter, the depths of the redox boundaries fluctuate. This contributes to a non-steady state. As a result of oxidation processes, a distinct peak in heavy metal concentrations in pore water is measured at the sediment-water interface. Because the studied anoxic sediments contain low levels of sulphide, other solid phases are expected to be of importance in the binding of heavy metals. Furthermore, heterogeneity of the sediment and complexation with dissolved organic compounds may result in supersaturation of the anoxic pore waters with respect to discrete heavy metal sulphides, thus influencing heavy metal mobility. Calculations using concentration gradients of heavy metals indicate that diffusive fluxes between the sediment and the surface water contribute to concentrations in the surface water, although significant effects may be confined to specific locations.

Heavy metal contamination to Poyang Lake is increasingly severe. Bellamya aeruginosas, the dominant species of bellamya in Poyang Lake, was chosen in this project to carry out a proteomics study, because they obtain nutrients from sediments directly and have a strong heavy metal enrichment capability. To get a better knowledge of the contamination level of Poyang Lake and a better understanding of toxicity and bioavailability of heavy metals contamination, the main heavy metals of surface sediments were tested and a proteomics study was carried out on bellamya aeruginosa, the dominant species of bellamya in Poyang Lake. Results of heavy metal tests show, to Poyang Lake, the most contaminated heavy metal is Cu, the widest contaminated heavy metal is Pb, the most contaminated area is the south lake area, and the least contaminated area is the entrance of Xioushui River. Proteomics analysis shows the main significantly different proteins are keratins or similar substances. These proteins are higher expressed in the samples obtained from the most contaminated area, so they could be the responding biomarkers for monitoring heavy metal contamination of surface sediment in Poyang Lake.

In southern Taiwan, almost all the main rivers have been contaminated by anthropogenic heavy metals and organic matters. The main pollution sources include agricultural, industrial, and domestic activities. River sediments potentially have large capacities to accumulate heavy metals and organic matters when the river water flows through it. The sediments sampled from high contaminated river (the Yenshui River) and moderately contaminated rivers (the Tsengwen, Chishui, Potzu, and Peikang Rivers) were used to realize correlations between each kind of aqua regia extractable heavy metals (Co, Cr, Cu, Zn, Ni, Pb, Mn, and Fe) and organic matters in vertical sediment cores. Organic matters and aqua regia extractable heavy metal concentrations, analyzed by strong acid-digested extraction, were determined in vertical profile segments from downstream sediments of the five rivers. Sum of six aqua regia extractable heavy metals (Co, Cr, Cu, Zn, Ni, and Pb) were below 3,000 mg/kg in sediments of the Yenshui River, and below 500 mg/kg in the other four rivers' sediments. Strongly positive correlations (r = 0.83-0.95) between each kind of aqua regia extractable heavy metals and organic matters (concentration range between 0.6 to 3.8%) were observed in sediments of the Yenshui River. The slopes of the linear regressive lines approximated the average metal complexation ratios with organic matters in the sediments. In sediments of the other four rivers, smaller positive correlation coefficients between aqua regia extractable heavy metals and organic matters (below 2.6%) were observed. The complexation ratios derived from the four moderately polluted river sediments were smaller than those derived from the highly contaminated river sediments, indicating that the importance of organic matters in the accumulation of heavy metals in river sediments.

AbstractSediment contamination in coastal areas with high anthropogenic pressure is a widespread environmental problem. Metal contaminants are of particular concern, since they are persistent and cannot be degraded. Microorganisms can influence metal mobility in the sediment by several direct and indirect processes. However, the actual fate of metals in the environment is not easily predictable and several biogeochemical constraints affect their behaviour. In addition, the geochemical characteristics of the sediment play an important role and the general assumptions for soils or freshwater sediments cannot be extended to marine sediments. In this paper we analysed the correlation between metal mobility and main geochemical properties of the sediment. Although the prediction of metal fate in sediment environment, both forex-situbioleaching treatments andin-situbiostimulation strategies, appears to require metal-specific and site-specific tools, we found that TOM and pH are likely the main variables in describing and predicting Zn behaviour. Arsenic solubilisation/increase in mobility appears to correlate positively with carbonate content. Cd, Pb and Ni appear to require multivariate and/or non-linear approaches.

Major metal-binding phases in the aerobic layer of sediments are iron and manganese oxyhydroxides (FeOOH and MnOOH) and particulate organic carbon (POC). The acid-volatile sulfide (AVS) model proposed for predicting nontoxicity from metals-contaminated sediments is only applicable to anaerobic sediments. In other sediments, normalization by POC or FeOOH and MnOOH may be predictive, but binding constants are not well understood. Metal mobilization is enhanced by ligand complexation and oxidation of anaerobic sediments. Free metal ion is the most bioavailable species, but other labile metal species and nonchemical variables also determine metal bioavailability; biotic site binding models have shown promise predicting toxicity for systems of differing chemistry. Hazard identification and ecological risk assessment (ERA) depend on determining bioavailability, from water (overlying, interstitial) and food, which can be done prospectively (e.g., normalized sediment chemistry, laboratory bioassays) or retrospectively (e.g., in situ bioassays, field studies). ERA of sediment-bound metals requires primary emphasis on toxicity and consideration of the three separate transformation processes for metals in the aquatic environment, the differences between essential and nonessential metals, the complex interactions that control bioavailability, adaptation, which may occur relatively simply without appreciable cost to the organism, weight of evidence, and causality.

Sediment cores were collected from four different mangrove areas of northern Kerala and southern Karnataka, western coast of India. The cores were analysed for the concentration of five heavy metals (Pb, Ni, Zn, Cu Fe) using Atomic Absorption Spectrometry. The levels of heavy metals in the present study from all the four sediment cores were in the order Fe > Pb > Zn > Ni > Cu and the mean concentrations of each elements in different cores were comparable. According to Sediment Quality Guidelines (SQG), the mangrove sediments analysed here were moderately contaminated with Ni and heavily contaminated with Pb. The increased concentration of Ni and Pb in the sediments might be due to their atmospheric deposition or water discharge from different far away sources since the areas selected for study were not disturbed by direct anthropogenic impacts. Elevated levels of Fe which is considered to be a common phenomenon in mangrove sediments have also been found in the present study. Heavy metal levels in sediments showed statistically significant correlations with pH, calcium carbonate and organic matter. This suggests the influence of physico-chemical parameters on the adsorption, deposition and persistence of heavy metals in mangrove sediments. The heavy metal concentration and the pollution status of the mangroves of west coast, especially the areas selected in this work are less studied before. Hence the data provide from the present baseline study would be further helpful in remediation and management of mangrove ecosystem.

Heavy metals contaminated sediment has become a worldwide environmental issue due to its great harm to human and aquatic organisms. Thus, economical, effective, and environmentally-friendly remediation technologies are urgently needed. Among which, combined remediation technologies have attracted widespread attention for their unique advantages. This paper introduces combined remediation technologies based on physical-, chemical-, and bio-remediation of heavy metal polluted sediments. Firstly, the research progress in physical-chemical, bio-chemical, and inter-organismal (including plants, animals, microorganisms) remediation of heavy metal polluted sediments are summarized. Additionally, the paper analyzes the problems of the process of combined remediation of heavy metals in river sediments and outlooks the future development trends of remediation technologies. Overall, this review provides useful technology references for the control and treatment of heavy metal pollution in river sediments.

Contaminated sediments pose a direct risk to sediment fauna and have the potential to affect other benthic assemblages. Disturbances that resuspend and remobilise contaminants may impact on filter-feeding, hard-substrate organisms that live immediately above sediments. This thesis uses laboratory and field manipulations to examine the impact of metal-contaminated sediments on sediment fauna and hard-substrate fauna simultaneously. It also compares the response of assemblages to metal contamination in a temperate and polar ecosystem. Simulated resuspension exposures in the laboratory indicated that contaminated sediments have the potential to affect hard-substrate organisms. Spirorbid polychaetes responded to both aqueous metals and to resuspended, particulate-bound metals. Impacts on hard-substrate fauna were however, not observed in manipulative field experiments using metal-spiked sediments. The recruitment and cover of hard-substrate organisms were either not affected or enhanced above contaminated sediments. In contrast, metal contamination had direct negative effects on sediment fauna, with a reduction in the abundance of most taxa. Results suggest that sediment fauna may interact with hard-substrate fauna through physical and/or biological mechanisms. In a reciprocal transplant experiment, established Antarctic hard-substrate assemblages were also unaffected by contaminant concentrations at an impacted site. Overall, metal-contaminated sediments are unlikely to pose as serious a threat to hard-substrate fauna as they do to sediment fauna. Contaminated sediments are not restricted to industrialised regions, and human activities in Antarctica have resulted in localised contamination near research stations. Although Antarctic assemblages are thought to be more sensitive than temperate assemblages to contaminants, few studies have explicitly examined this. Little evidence was found to support the theory that Antarctic assemblages are more susceptible to contaminated sediments. The response of Antarctic and temperate assemblages in the field to metal-contaminated sediments over a 10-11 month period was comparable. Responses were of a similar magnitude, despite differences in the composition of assemblages. In 10-d toxicity tests, the mortality of a common Antarctic hard-substrate organism was relatively insensitive to aqueous Cu, Zn and Pb. These results suggest that using current sediment quality guidelines from Australia may be a useful screening tool to assess the risk associated with contaminated sediments in Antarctica.

Climate change predictions indicate an increase in the frequency and duration of flood events along with longer dry antecedent conditions , which could alter patterns of trace metal release from contaminated river bank sediments. This study took a laboratory mesocosm approach. Chemical analysis of water and sediment samples allowed the patterns of Pb and Zn release and key mechanisms controlling Pb and Zn mobility to be determined. Trace metal contaminants Pb and Zn were released throughout flooded periods, however the highest concentrations of dissolved Pb were observed at the end of the longest flood period and high concentrations of dissolved Zn were released at the start of a flood. These concentrations were found to exceeded environmental quality standards. Key mechanisms controlling mobility were (i) anglesite solubility control of dissolved Pb, (iii) evaporation, precipitation and dissolution of Zn sulphate salts, (iii) oxidation of galena and sphalerite, (iv) reductive dissolution Mn/ Fe hydroxides and co precipitation/adsorption with Zn. In light of climate change predictions these results indicate future scenarios may include larger or more frequent transient 'pulses' of dissolved Pb and Zn released to river systems. These short lived pollution episodes could act as a significant barrier to achieving the EU Water Framework Directive objectives.

Sediments can act as both a sink for pollutants and a source for aquatic contaminants. Natural and human disturbances of the sediments can release the contaminants to the overlying water where bottom dwelling, or benthic, organisms may be exposed through direct contact, ingestion of sediment particles, or uptake of dissolved contaminants present in the water. Dredging, the most common remediation technology for heavy metals, exacerbates this process. The in situ use of emulsified metal has been studied for its ability to pull heavy metals from aqueous solution and from saturated soils. It has proven successful in the laboratory with removal of lead, cadmium, copper, nickel, and uranium from aqueous solution and removal of lead and cadmium from saturated spiked soils. The use of zero-valent metal particles, particularly those of zero-valent iron (Fe0), as an in situ remediation technique, is currently undergoing evaluation. The basic mechanism for removal appears to be reduction of contaminant metals followed by the subsequent precipitation of their insoluble forms. This is accompanied by the oxidation of the zero-valent metal. In the case of iron, Fe0 undergoes oxidation to Fe2+ and then to the Fe3+ state. Particulate Fe0 has been shown to precipitate Cr6+ to Cr3+ and Pb2+ undergoes reduction to Pb0. Initially, zero-valent iron filings were used to reduce the metal contaminants, but it has been shown that smaller size iron particles, such as nano-scale iron, have higher initial reduction rates as well as a higher concentration of contaminant removal per mole of iron. Emulsion liquid membrane (ELM) technology has been employed as a remediation technique for the removal of metals from wastewater where extraction and stripping processes are performed in a single operation. The ELMs are made by forming an emulsion between two immiscible liquids, such as oil and water, and are often stabilized by a surfactant. We have attempted to demonstrate the application of the combination of these two technologies through the use of emulsified zero-valent metal (EZVM) to treat sediments with heavy metal contamination. Emulsions were prepared using vegetable oil, water, Span 85, and either nanoscale Fe, 1-3 [micro]m Fe, 4 [micro]m Mg, or a 20 wt % Fe-Mg mixture. The results presented in this study demonstrate that EZVM is a viable technique for in situ remediation of heavy metals in sediments. Laboratory scale studies have shown high levels of removal of lead and cadmium from solution using emulsified zero-valent iron. Additionally, the use of emulsified magnesium has shown the ability for high levels of removal of copper, cadmium, nickel, lead, and uranium from solution. A variety of solution matrices were also explored for a lead solution including seawater, the presence of complexing agents and humic acids. Small-scale laboratory studies have shown 65% removal of lead and 45% removal of cadmium from saturated, spiked soils. A bench scale test to demonstrate the applicability of this technique in the environment revealed similar results for the removal of lead.
M.S.
Department of Chemistry
Arts and Sciences
Industrial Chemistry

Three approaches were employed to examine the effects of elevated sediment trace metal concentrations on estuarine/marine macrobenthic invertebrate assemblages. The initial study examined macroinvertebrate communities along a known polymetallic gradient, Lake Macquarie, NSW (gradient study). The second study experimentally tested if sediments sourced from different locations within Lake Macquarie differentially influenced the recolonisation of benthic invertebrates. The third study investigated the different recolonisation patterns of benthic invertebrates into sediments spiked with increasing concentrations of sediment-bound cadmium. In the Lake Macquarie gradient study, four locations (Cockle Bay, Warner's Bay, Kooroora Bay and Nord's Wharf) were sampled in winter 2000 and summer 2003 using a hierarchical design (location > site > plot). On both sampling occasions, the sediments showed strong gradients in lead, cadmium and zinc concentrations emanating from the Cockle Bay industrialised region in the lake's north, with concentrations being significantly lower in the most southern and less urbanised location (Nord's Wharf). In general, concentrations of lead, cadmium and zinc in the sediments increased among locations in the following order: Nord's Wharf > Kooroora Bay > Warner's Bay > Cockle Bay. AVSJSEM analyses indicated that in some sites in Cockle Bay, and to a lesser extent Warner's Bay, SEM concentrations exceeded their molar equivalence of AVS, indicating the potential for trace metals to be labile within the porewaters. Granulometry also changed along the gradient, with a higher proportion of silt/clay occurring in the locations with high metal concentrations. Conversely, the percentage of total organic carbon was higher in the less contaminated locations. In winter 2000, changes in benthic communities along the gradient supported the a priori hypotheses, with diversity and richness being greater in locations with lower concentrations of metals. Polychaetes were most numerous in Cockle Bay and Warner's Bay, whilst bivalves and gastropods were more abundant in Nord's Wharf and Kooroora Bay. Crustaceans were more numerous in Nord's Wharf; with all other locations having similar, lower, abundances. Ordination maps of the assemblages provided relatively clear separation of the assemblages among locations, with nonparametric multivariate analysis of variance (NPMANOVA) and subsequent pair-wise comparisons finding significant differences among the assemblages from all locations. SIMPER analyses found the highest level of dissimilarity was between the Nord's Wharf and Cockle Bay assemblages - primarily attributable to differences in the relative contributions of isopods; tellenid bivalves; and the polychaete families Spionidae, Opheliidae and Nephytidae. Weighted Spearman rank correlations (BIOENV) identified cadmium (Pw =0.74) as the strongest environmental (single or combination) variable to correlate with biotic assemblages. Benthic patterns along the gradient were less defined in summer 2003 due to a dramatic reduction in the abundance and diversity of fauna in Nord's Wharf. This decline was possibly attributable to a sustained reduction in salinity caused by a prolonged rainfall event. With the exception of Nord's Wharf, trends in the community indices and abundances of key taxa among the other locations were similar to those reported in winter 2000. Multivariate analyses discriminated the benthic assemblages from the four locations, with the findings from the NPMANOVA pair-wise comparisons indicating that the assemblages from all four locations were significantly different. SIMPER analyses showed the highest level of dissimilarity was between Nord's Wharf and Warner's Bay, with these differences being primarily attributable to their relative abundances of amphipods and polychaetes from the families Spionidae, Cirratulidae, Opheliidae and Capitellidae. BIOENV found that the combination of the sedimentary concentrations of cadmium and iron provided the best correlation (Pw =0.73) with biotic patterns, with similar correlations occumng with the addition of lead and its covariate, zinc (Pw =0.72). The combined findings from the gradient study established a strong correlation between trace metal concentrations within the sediments and suite of univariate and multivariate measurements. The low abundance and diversity of fauna in Nord's Wharf in the summer of 2003 highlighted the dynamic changes which can occur in the distributions of macrobenthic invertebrates. Although the study indicated that there was a strong relationship between trace metal concentrations and benthic community structure, the study was correlative, and requires subsequent experimental testing to confirm the causality of the observed relationships. The second component of the research was a translocation experiment using benthic recolonisation as an end-point. The experiment was performed to identify if the sediments, and not location, were influencing the composition of benthic assemblages in Lake Macquarie. Sediments were collected from three locations (Cockle Bay, Warner's Bay and Nord's Wharf), defaunated, and transplanted in three new locations along the south-east edge of the lake. At each location, 10 containers of each treatment were randomly placed in the sediment and allowed to recolonise for 22 weeks. Upon retrieval, the benthic communities were sampled and enumerated in conjunction with a variety of chemical and sedimentary measurements. Ten replicate invertebrate samples were also collected in the sediments adjacent to the experiment (ambient samples) at the completion of the experiment. Due to human interference, the containers from only two locations were analysed. Upon retrieval, pH and redox profiles of the sediments were similar to those expected in natural sediments. In general, concentrations of metals were low in the porewaters; however, iron precipitation on the porewater collection devices may have artificially increased the diffusion of metals, increasing concentrations near the sediment-water interface. Concentrations of SEM exceeded their AVS equivalence in some samples taken from the Cockle Bay and Warner's Bay treatments. Two-way ANOVAs found significant interactions between location and sediment treatments in diversity, evenness and the number of polychaetes, as well as significant differences in the number of capitellids and crustaceans among locations. Post-hoc comparisons of means found the Nord's Wharf sediment contained a higher mean number of individuals than the other treatments, including the ambient samples. nMDS ordination plots for both locations provided poor graphical discrimination of the assemblages among treatments; however, NPMANOVA detected significant location and treatment interactions. In both locations, pair-wise comparisons indicated that the assemblages within the Nord's Wharf treatments were significantly different to the Cockle Bay, Warner's Bay and ambient assemblages. No significant differences were detected between the Cockle Bay and Warner's Bay assemblages at either location. SIMPER analyses found the highest level of dissimilarity occurred between the ambient assemblages in Location 2 and the Nord's Wharf treatment, primarily due to the relative difference in the abundances of Capitellidae, Spionidae, Oweniidae, Nereididae and isopods among the assemblages. The findings from the translocation experiment suggest that the sediments are influencing the recolonisation of benthos. However, because differences were not detected between the Cockle Bay and Warner's Bay treatments, the approach used in the study shows potential as an in situ technique which could be used to assess the potential ecological risks of sediments fiom specific locations. Excluding cost and time considerations, the technique's primary disadvantage is the lack of a true control. As a result, the technique can only identify if the sediments are modifying benthic recolonisation, and not causality. The final component of the research experimentally tested if elevated concentrations of sediment-bound cadmium affected benthic invertebrate recolonisation. Sediments from the south coast of New South Wales (Durras Lake) were defaunated, and spiked with cadmium under anaerobic conditions to obtain three targeted cadmium concentrations: control (