Mn Oxide Fractions Research Articles

Weathering as a control on the triple oxygen isotopes of groundwater-associated ferromanganese deposits: lessons from the Grimlock Ni–Co–Mn prospect, Northern Territory, Australia

At the Grimlock laterite deposit (Northern Territory, Australia), Co and Ni mineralization occurs mainly in the Mn-oxide rich layers of the ferromanganese (Fe-Mn) crust overlying ultramafic bedrock. Groundwater-associated Fe-Mn crusts consist of mineral (e.g. Mn-oxide, Fe-oxyhydroxide and silicate) groups suitable for studying triple oxygen isotopes and present unique interpretative challenges (e.g. small Mn-oxide fractions relative to Fe-Mn precipitates from other formation environments and extensive weathering). We evaluate triple oxygen isotopes within the context of changes to properties (i.e. mineralogy, major and trace element geochemistry, and degree of weathering) of a lateritic profile. We use pre-existing mineral-water fractionation factors, meteoric water δ 18 O and temperature data to calculate δ 18 O values of fully altered mineralogical endmembers, then, using mass balance, discuss scenarios to elucidate measured whole-rock δ 18 O values. The δ ′ 18 O (′ denotes linearized notation) and Δ ′ 17 O of near-surface samples (0–8 m) are generally lower (mean of 8.892‰) and higher (mean of −0.141‰), respectively, than the δ ′ 18 O (mean of 12.767‰) and Δ ′ 17 O (mean of −0.176‰) of samples from greater depths (19–22 m). At 16–17 m depth, δ ′ 18 O and Δ ′ 17 O are relatively high (means of 17.509 and −0.118‰, respectively). The measured whole-rock δ 18 O values are explainable by substituting lower δ ′ 18 O values for the Mn-oxide and Fe-oxyhydroxide fractions, and higher δ ′ 18 O values for the aluminosilicate fraction, changes coinciding with greater alteration. These results suggest that mineral weathering is primarily responsible for observed variations in the triple oxygen isotopes of groundwater-associated Fe-Mn crusts, rather than variation in the initial source of oxygen incorporated into Mn-oxide. Supplementary material: Grimlock sample photographs, XRD patterns and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7071907

MIGRATION OF HEAVY METALS FROM MINE WASTE ROCK DUMP END ENVIRONMENTAL IMPACT ON GROUNDWATERS AND SEDIMENTS

The environmental impact of mine waste rock dump, located in the region of Srednogorie, Bulgaria on groundwaters and sediments was studied. The acid mine drainage with low pH (2.43 - 3.53), high electrical conductivity (1500 - 4400 μS cm-1), content of Fe, Mn, Cu, Zn, Al, As and high concentration of sulfates (540 - 6905 mg L-1) are formed after heavy rainfall. The content of heavy metals, except manganese, in groundwater was significantly lower than that in the acid mine drainage, and the pH was in the range of 5.43 to 6.62. Sediments in the non-consequential vicinity of the mine waste rock dump had a pH in the range of 2.86 - 4.53 and contained heavy metals and As at concentrations higher than those in the mineral waste due to precipitation, co-precipitation and sorption reactions. An increase in the copper and zinc content in the exchangeable and organic matter fractions was found in the sediment sample. A relationship was found between arsenic and iron concentration in the sediments, which was mainly due to the retention of arsenic in the Fe and Mn oxides fraction. The concentration of total Mn in the sediments was lower than that in the mining waste due to the high mobility of manganese.

Rape Straw Biochar Application Enhances Cadmium Immobilization by Promoting Formation of Sulfide and Poorly Crystallized Fe Oxide in Paddy Soils

The mechanisms of rape straw biochar that affect the fixation of cadmium (Cd) in paddy soil by influencing redox of iron and sulfur are unclear. Several anaerobic incubation experiments were carried out using Cd-contaminated paddy soils (LY and ZZ). Rape straw biochar at pyrolysis temperatures of 450 °C (LRSB) and 800 °C (HRSB) was selected as the soil remediation agent. The electron exchange capacity and electrical conductivity were higher in HRSB than those in LRSB. The lower pe + pH in HRSB enhanced Fe oxide reduction, with a maximum increase in Fe2+ of 46.0% in ZZ. Compared to treatment without biochar (CK), the poorly crystallized Fe oxide (Feo) in HRSB increased by 16.8% in ZZ. This induced Cd bound to Fe, and Mn oxides fraction (Fe-Mn Cd) increased by 42.5%. The SO42−-S content in LRSB was 4.6 times that of HRSB. LRSB addition increased acid-volatile sulfide by 46.4% and 48.9% in LY and ZZ soils, respectively, compared to CK. This resulted in an increase in sulfide’s contribution to Cd fixation, with values rising from 24.2% to 37.8% in LY and 19.1% to 29.8% in ZZ. Overall, LRSB reduced Cd mobility by forming more sulfide, while HRSB increased Fe-Mn Cd by increasing Feo.

Early diagenetic mobilization of rare earth elements and implications for the Ce anomaly as a redox proxy

The Rare Earth Elements (REE) archived in carbonate rocks retain a wealth of information on paleo-seawater chemistry and local-regional redox conditions. However, interpretations are often ambiguous due to the potential for REE remobilization in marine environments. In this regard, many carbonate rocks that retain primary seawater isotopic signatures exhibit non-seawater-like REE patterns, implying either unusual REE behaviour in seawater or diagenetic overprinting of otherwise well-preserved rock samples. Here, we apply sequential leaching to constrain the possible effects of different REE-bearing phases on measured carbonate REE patterns in order to address this quandary. Our results show that the exchangeable phase contains negligible REE, but could be an important host phase for other elements such as Sr, Ba and K. The acidified hydroxylamine hydrochloride leach is shown here not only to dissolve Fe–Mn oxides but also phosphate minerals, which induces middle REE enrichment in corresponding leachates of dolostone samples in our study. The demonstrable Fe–Mn oxide phase in limestone samples is characterized by middle and/or light REE enrichment and positive Eu anomalies, which are attributed to hydrothermal processes and continuing exchange with marine fluids after initial precipitation. The non-seawater-like REE patterns observed in the carbonate phase of otherwise well-preserved limestones resemble those of the co-existing Fe–Mn oxide fraction, and are interpreted to reflect the dissolution of REE carrier phases during early diagenesis. This view is supported by fluid-rock interaction modelling, which shows how REE can be mobilized at relatively low fluid/rock ratios in shallow porewaters. Non-seawater-like REE patterns may therefore be caused by the incorporation of REE from shallow porewaters before final lithification due to an elevated flux of particulate REE carrier phases, e.g. Fe–Mn oxides and organic matter, to the seafloor. In spite of the sensitivity of carbonate REE patterns to early diagenetic exchange, the co-occurrence of non-seawater-like patterns with primary strontium and carbon isotope values suggests that REE should not be viewed as a general indicator for the preservation of other geochemical proxies. Importantly, Ce anomalies of the carbonate phase will also be affected by porewaters, masking primary seawater values. Our results favour a reevaluation of redox interpretations by taking into account REE patterns as a whole.

Distribution, speciation and mobility of metals in sediments of the Tianxiu hydrothermal field, Carlsberg Ridge, Northwest Indian Ocean

Tianxiu is the only ultramafic-hosted hydrothermal field that has been discovered on the slow-spreading Carlsberg Ridge (CR), northwest Indian Ocean. Sequential extraction has been performed on the surface sediments from the near-vent and far-field of Tianxiu to characterize the compositions of metalliferous sediments, the speciation of selected metals and the potential risks of metal mobility. The near-vent sediments of Tianxiu are mainly derived from hydrothermal inputs and are enriched in Fe, Zn, P, Pb, Mo and especially Cu, Mg, Co and Ni with significantly higher contents compared to metalliferous sediments formed in basalt-hosted hydrothermal systems. Most of the ore-forming elements (Fe, Cu, Zn, Mn, Co and Ni) and rare-earth elements (REEs) exist in the residual fraction and Fe Mn oxide fraction, followed by the carbonate fraction and organic fraction. The chondrite-normalized REE pattern in each phase is characterized by relative enrichment in light (L)REEs and positive Eu anomalies, consistent with the REE patterns of hydrothermal fluids. The far-field sediments of Tianxiu are mainly derived from background pelagic sedimentation while the sediments at some sites are influenced by a small amount of hydrothermal plume fallout. The investigated elements mainly exist in the Fe Mn oxide fraction, residual fraction and carbonate fraction. In particular, ore-forming elements Cu, Pb, Mn, Co and Ni are mostly enriched in the Fe Mn oxide fraction, which is attributed to their adsorption by hydrothermal particulates in the plumes. The potential mobility of each metal is evaluated in terms of its total content in the unstable phases, which reveals that most of the heavy metals (e.g., Cu, Zn, Mn and Pb) in the metalliferous sediments have high potential mobility (> 50%). • Heavy metals are particularly enriched in the near-vent sediments. • Heavy metals are mainly present in the residual fraction and Fe Mn oxide fraction. • Most of the heavy metals in the near-vent sediments have high potential mobility.

Phosphate adsorption kinetics and equilibria on natural iron and manganese oxide composites

Although it is well known that phosphate retention in soils and sediments is strongly influenced by binding to secondary iron oxides, there have been relatively few studies examining its adsorption/desorption behavior on multicomponent particles of realistic natural complexity. In this study, natural Mn-rich limonite (LM), was used to prepare naturally complex Fe- and Mn-oxide composite materials to examine phosphate adsorption/desorption. To clarify the role of the Mn-oxides, results for the LM sample were compared to those for an acid treated version (LAT), in which the acid-extractable Mn-oxide fraction has been selectively eliminated while leaving the Fe-oxide fraction intact. The saturated adsorption capacity on LAT was almost double that on LM, suggesting that phosphate adsorption to the iron oxides is strongly occluded by the Mn-oxide fraction. This result is reinforced by the comparing the pH dependence and fits to adsorption isotherms, and by desorption experiments and STEM-EDS mapping showing that phosphate loading on Mn-oxides was limited. Hence, although the collective results confirm that phosphate uptake and strong binding is selectively controlled by the Fe-oxide fraction, our study reveals that the Mn-oxide fraction strongly interferes with this process. Therefore, phosphate uptake behavior on metal oxides cannot be predicted solely on the basis of the Fe-oxide fraction present, but instead must take into account the deleterious impacts of other intimately associated phases. For co-diagenetic Fe/Mn-oxide composites in particular, Mn-oxides appear to severely limit phosphate uptake on the Fe-oxide fraction, either by hindering access to binding sites on the Fe-oxide or by lowering their affinity for P.

Relationship of Selected Soil Properties with the Micronutrients in Salt-Affected Soils

The present study aimed to assess the relationship of soil properties in salt-affected soils. The soil samples were collected from 14 districts of Pakistan. Soil salinity and sodicity are the common features of the arid and semiarid regions. The effects of the salt’s interactions with soil micronutrients have not been well studied. Therefore, saline and non-saline soil samples were collected from different locations. The microelements (Fe, Cu, Mn, and Zn) were fractionated into water-soluble, exchangeable, carbonate, Fe + Mn oxide, organic, and residual fractions. Univariate and multivariate analysis (PCA) was carried out to determine the linear relationship between soil properties and micronutrients fractions. Results showed that the magnitude of micronutrients appeared to be affected by the salinity in soils. In saline soil, the Fe fractions differed in the order of residual > organic bound > Fe + Mn bound > carbonate bound > exchangeable > water soluble. Iron fractions varied in the non-saline soils as residual > Fe + Mn bound > organic bound > exchangeable > carbonate bound > water soluble. Copper concentration was higher in the residual and carbonate forms, and the amount was lower in the exchangeable and water-soluble forms under both saline and non-saline conditions. The water-soluble Mn fraction was lower, and the residual Mn fraction was proportionately higher than other forms of Mn in soils. Zinc was found mostly in the residual fraction in both saline and non-saline soils. The mobility factor of micronutrients in non-saline soil was greater than in saline soil. PCA revealed that organic matter (OM) and pH directly affected the fractionation of Cu, Mn, Zn, and Fe in soil. Thus, it could be inferred that salts can bring changes to the composition of micronutrients depending on the nature of the soil and the magnitude of salts.

Vinegar residue biochar: A possible conditioner for the safe remediation of alkaline Pb-contaminated soil

A better understanding how to modulate alkaline soil-plant systems with lead (Pb) toxicity with by vinegar residue biochar is important for the remediation of Pb-contaminated soil. Leaching column and pot experiments were conducted to investigate the effect of vinegar residue biochar on Pb speciation, soil properties, and plant growth under Pb stress. The results indicate that biochar could effectively decrease the exchangeable and carbonated-bound Pb but increase the Fe–Mn oxide and residue fractions in the soil with Pb at 500 mg kg−1. Biochar did not effectively immobilize Pb in the soil with Pb at 1000 mg kg−1. After leaching, biochar evidently increased the organic carbon and dissolved organic carbon content of the soil, but slightly affected the pH, cation exchange capacity and carbonate content. The biochar addition at 0.5% had no significant effect on soil aggregates, and biochar at 2.0% and 5.0% significantly decreased soil aggregate stability. The dry weight and soluble protein content of pak choi (Brassica chinensis L.) increased with biochar treatment. Lead assimilation by plants was inhibited by the decreased availability of Pb in biochar-treated soils. Soil enzymes activities also significantly increased, then facilitated biochemical reactions in the soil environment. The applied biochar has shown an important role in mitigating Pb toxicity by increasing the soil organic carbon, dissolved organic carbon content, enzyme activities, and plant growth. The low dose biochar (0.5–2.0%) are recommended as references for subsequent experiments, especially in alkaline loam soil.

Chemical speciation, bioavailability and risk assessment of potentially toxic metals in soils around petroleum product marketing company as environmental degradation indicators

The study aims at investigating chemical speciation, bioavailability and risk assessment of some selected metals in soils around refined petroleum depot using the concentrations of the metals as variables to ascertain the impacts of the activities within the petroleum depot. Surface-soils (0–15 cm) were collected from within the premises of Pipelines and Product Marketing Company, Ibadan, Nigeria, while control samples were collected at 200 m away from the study location. Electrical conductivity and pH were measured using a calibrated dual purpose meter, while elemental analysis was done using Atomic absorption spectroscopy analytical technique. The results showed that the soils exhibited low ecological risk; minor enrichment for Mn, moderately severe enrichment for Ni and Co, severe enrichment for Cr and extremely severe enrichment for Pb, Zn and Cd. There was low contamination factor for Pb, Ni, Mn, Cr, Co, and Fe and moderate contamination by Zn and Cd. Geo - accumulation index results indicated unpolluted with Ni, Mn, Cr, Co, and Fe, unpolluted to moderately polluted with Pb and Zn and moderately to strongly polluted with Cd. Inter-element clustering results indicated chemical affinity and/or similar genetic origin among the elements. Speciation analysis suggested that Fe, Co, Cr, Cd, and Ni occurred in the residual fraction; Pb, and Zn in the carbonate fraction, while Mn have its highest percentage in the Fe–Mn oxides fraction. Percentage mobility and bioavailability showed that most of the metals are immobile and non-bioavailable. Study concluded that the oil-impacted soils were contaminated with most of the metals, but with low ecological risk.

Manganese fractionation analysis in specific soil and sediment samples

Manganese has been determined in soil- and sediment samples taken from selected regions with high manganese concentrations anthropogenic and/or geogenic. The total content of manganese in chosen sediment- and soil samples has been determined applying FAAS after microwave digestion and the manganese fractions after sequential extraction procedures using galvanostatic stripping chronopotentiometry. The highest content of manganese has been determined in sediment from Hôrka (6243.6 ± 56.2 mg kg-1), while the lowest value has been obtained in the sediment from Kráľová (278.6 ± 3.9 mg kg-1). Using a modified Tessier’s procedure it was found, that manganese in sediments from Kráľová is associated mainly with the carbonate fraction (>50%), while in sediments from Lozorno and Hôrka it is associated primarily with the Mn and Fe oxide fraction (80% and 42% respectively).

Speciation and correlation of boron and lithium in surficial sediments of the eastern and western Taijinar Salt Lake

The eastern/western Taijinar Salt Lake in Qaidam Basin is rich in lithium and boron resources. Chemical speciation of boron and lithium is conducive to identify the migration way and enrichment of heavy metals which might cause certain effects on the environment of salt-lake area. A total of 28 surface sediment samples were collected from the Taijinar Salt Lake in June of 2020 to investigate the distribution, speciation and sources of boron and lithium in salt-lake sediments. The results showed that the average content of boron/lithium was low with value of 1.6/3.4 µg kg−1, while that of the other elements in sediments ranging from 0.035 µg kg−1 (Cd) to 48.20 mg kg−1 (As) by following the order of As > Pb > Hg > Zn > Cr > Cd. Boron and lithium in sediments were mainly bound to Fe–Mn oxide and residual fractions with the average proportion of 29.87% and 35.36% for boron as well as 32.18% and 31.43% for lithium. Pb mainly existed in carbonate and residual fraction, while Zn mainly existed in the Fe–Mn oxide and residual bound with average value of 40.56% and 43.32%, respectively. Hg/Cr mainly existed in the residual with the average value of 58.68%/84.18%, while Cd mainly existed in the Fe–Mn oxide and residual fraction with an average proportion of 26.52% and 30.89%, respectively. As mainly existed in Fe–Mn oxide, residual, and organic fraction with an average proportion of 30.20%, 32.61% and 21.92%, respectively. Elements including Zn, Cr and Pb had a certain influence on the speciation of boron and lithium based on the correlation analysis. The enrichment of Cd, Cr and Pb might be mainly caused by anthropogenic sources. The findings of this study will provide some basic information on the important elements including lithium and boron in the salt-lake areas.

Stabilized green rusts for aqueous Cr(VI) removal: Fast kinetics, high iron utilization rate and anti-acidification

Green rusts (GRs) are redox active towards contaminants but they are not stable for long distance transport during the soil and groundwater remediation. In this study, green rust chloride (GR) was stabilized by selected regents, including silicate (Si), phosphate (P), fulvic acid (FA), carboxymethyl cellulose (CMC) and bone char (BC), then these stabilized GR, collectively named GR-X, would be further applied for Cr(VI) removal from aqueous solution. The stabilization experiment demonstrated that the release of Fe(II) from GR was effectively suppressed by above reagents, enabling at least 50% lower Fe(II) leaching from the stabilized GR-X than that from the pristine GR. The intact hexagonal GR plates and crystallinity were also confirmed by the SEM images and XRD patterns after storage for 7 days, indicating the stable structure of GR-X was remained. In the Cr(VI) removal tests, Cr(VI) was eliminated by GR-X in seconds with a Fe(II) utilization efficiency over 90%. The Cr species examination demonstrated that the GR-X was able to transfer Cr(VI) into stable Cr(III)–Fe(III) precipitates (Fe–Mn oxides fraction). After Cr(VI) removal tests, all reactors were exposed to the air for 1 week to monitor pH fluctuation and evaluated the risk of acidification. The results indicate that, except for GR-Si system, the other post-remediation systems are stable and the pH buffering ability of GR-X could avoid acidification and lower the Cr leaching risk.

CHEMICAL FORMS OF Zn, Mn, Fe and Pb IN SOIL SAMPLES FROM THE VICINITY OF SOME MAJOR DUMPSITES IN GOMBE METROPOLIS, GOMBE STATE NIGERIA

This research work is aimed at determining the chemical speciation of metals Zn, Mn, Fe and Pb in soil samples from three major dumpsites within Gombe metropolis, Gombe state. The renowned five steps Tessier sequential extraction method was employed in the extraction of the heavy metals. The metals were extracted into five fractions namely: Exchangeable (F1), carbonate bound (F2), Fe-Mn oxide bound (F3), Bound to organic matter (F4) and the residual fraction (F5) in order of decreasing mobility. The elemental analysis of the fractions was carried out using atomic absorption spectrometric technique. The results showed Zn was predominantly bounded to the exchangeable fraction with 32.66±0.31 mg/kg (54.18%) and least in the Fe – Mn oxide fraction with 0.01±0.00 mg/kg (0.02%). The trend in its abundance is in the order F1> F2>F5>F4>F3. Mn was predominantly associated with the bound to carbonates fraction with the value of 103.3.±3.30 mg/kg (56.14%) and least in the exchangeable with the value of 1.30±1.85mg/kg (2.13%) its occurred in the order F2>F3>F4>F5>F1. The concentration of Fe was highest in the residual fraction with the value of 25.90±1.75mg/kg (45.45%)and least in the carbonate bound fraction wi th 5.10±0.40 mg/kg (2.13%) the order is F5>F4>F3>F2>F1. Pb was not detected in most of the fraction but highest in bond to carbonate and bond to organic matter fraction with the values of 6.64±4.12 mg/Kg (70.64 %) and 2.76±0.10 mg/Kg (29.36 %) respectively in two different samples. It was however established that Zn, Mn and Pb were mostly associated with the first three fractions thus, showed high bio-availabilty whereas Fe was found in the residual fraction and is expected to be low in mobility and less bioavailable.

Influence of coal gangue aided phytostabilization on metal availability and mobility in copper mine tailings

Copper mine tailings without proper remediation deposited permanently in tailings ponds would pose adverse impacts to the environment. Coal gangue, with high nutrients, used in infertile soil, is investigated in microcosm trials to explore the possibility of immobilize metals within the copper mine tailing in this research. Therefore, a pot trial was conducted using coal gangue and Vetiveria zizanioides for phytostabilization of the metals in copper mine tailing. Results indicated that applying coal gangue not only increased the pH, organic matter content and nutrient contents of the amended tailings, but also decreased the DTPA-extractable concentrations of Zn, Pb, Cd, and Cu in the amended tailings. The application of coal gangue converted the exchangeable and carbonate fractions of Zn, Pb, Cd, and Cu into unavailable forms of Fe–Mn oxide and/or organic matter fractions, thus reducing those metal contents in mobile fractions of the amended tailings. This study shows that treatments with coal gangue inhibited Zn, Pb, Cd, and Cu translocation from tailings to Vetiveria zizanioides. In contrast, the accumulation of Cr in the plant was increased by the addition of coal gangue. Collectively, these results support the hypothesis that coal gangue is a potential waste-derived amendment with the ability to reduce the mobility of most of the studied metals in copper mine tailings. This study also proposed a new approach to dispose the waste of coal gangue as an amendment for phytostabilization of copper mine tailings.

Effects of a native earthworm species (Amynthas morrisi) and Eisenia fetida on metal fractions in a multi-metal polluted soil from South China

The effects of the native species Amynthas morrisi and the composting earthworm Eisenia fetida were evaluated on the forms of Zn, Cd, Pb and Cu in a long-term contaminated Chinese soil, with and without added organic matter (OM), in a 60-day laboratory experiment (25 °C field capacity). Four metal fractions were extracted using a sequential procedure: water-soluble exchangeable and carbonate-bound fraction (WAEX), Fe and Mn oxides fraction (FMOX), organic compounds (ORGA), and residual non-extractable fraction (RESI). The sum of available fractions (AVA = WAEX + FMOX + ORGA) and the total contents of the surface casts and non-ingested soil were calculated. In all treatments, all casts of the two earthworm species had higher pH and DOC (Dissolved organic carbon) contents and lower Eh values than those of their respective controls. Amynthas morrisi casts contained higher concentrations of available forms (AVA) of Cd (+84.1%) and Zn (+39.9%) and lower concentrations of available Cu (−10.1%) than those in the control soil (P < 0.05). Organic matter addition limited the variations of pH, Eh and DOC and had the opposite effect to earthworms on metal speciation. However, in the soils of all experimental units and compared with control soil, earthworms increased organically bound Pb (+16.0%) and Cu (+46.1%, A. morrisi; 64.0%, E. fetida), whereas other extractable forms of elements decreased, depending on the metals and their chemical forms (P < 0.05). Amynthas morrisi had similar effects on metal dynamics to the exotic E. fetida and reproduced when organic matter was added; both are therefore good candidates for soil phytoremediation technologies based on increased earthworm activities.

Speciation of heavy metals in bottom sediments of a drinking water reservoir for Gdańsk, Poland – changes over the 14 years

There was conducted a comparative study of the concentrations of heavy metals (Zn, Cu, Pb, and Cd) in the surface layer of sediments collected in two investigation periods: 1999–2000 and 2013. The results demonstrated that the degree of metals pollution decreased over time. The contamination factors (Cf) calculated for Zn, Cu, Pb, and Cd were respectively 3.63, 3.86, 3.23, and 3.25 in the first period of research and 1.35, 3.42, 1.98, and 1.43 in the second one. The metal speciation analysis indicated that Zn was mainly associated with the Fe–Mn oxides fraction and the residual fraction, and Cu – with the residual fraction and the organic fraction in both periods of investigation, while the percentage of geochemical fractions in binding of Pb and Cd changed in time. The share of fractions Fe–Mn oxides/carbonate increased in the case of Pb, and carbonate/exchangeable fractions in the case of Cd. The risk assessment code (RAC) decreased in the following order: Cd > Zn > Pb > Cu and was higher in 2013 - achieved the very high-risk category in the case of Cd. Thus, despite the decrease of sediment pollution, RAC for Cd increased due to changed geochemical speciation.

Changes in the total content and speciation patterns of metals in the dredged sediments after ocean dumping: Taiwan continental slope

The aim of this study was to understand the changes in heavy metals and speciation patterns in the dredged sediments after ocean dumping by a five-step sequential extraction procedure. The potential mobility and bioavailability of heavy metals in the sediments were also assessed. The results showed that the average contents of heavy metals, Cu, Zn, Ni, Cd, Cr, and Pb, in the dredged sediment of Kaohsiung Harbor are 120, 403, 33, 0.46, 112, and 40 mg/kg dw, respectively. The Cd and Zn basically bound in the carbonate fractions of the dredged sediments, which accounts for 36% and 45% of their total content on average. The highest level of Cu was present in the organic-matter fraction (92%), Cr and Pb were present in the Fe–Mn oxides fraction (59% and 52%) of the dredged sediments, and the most of Ni (52%) was found in the residual fraction of sediments. Except for Ni, the total amount of all heavy metals in the dredged sediments of Kaohsiung Harbor was about 1.5–4 times higher than the surface sediment of the ocean disposal site. The speciation patterns of heavy metals in the surface sediments of disposal site were similar to those of the reference site, whereas were distinctly different with the dredged sediments. The observation implies that the dredged sediments after dumping in the ocean disposal site, their heavy metals could be diluted by the physical and chemical effects in the marine environment and eventually to the stable state.

Assessment of sediment quality using total and bioavailable concentration of metals in intertidal mudflats of a tropical (Vashishti) estuary, west coast of India

The mudflat sediment cores collected from lower (VS-1) and middle (VS-2) regions of the Vashishti estuary were sub-sampled at 2-cm intervals and analyzed to determine grain size, organic carbon, and total metal (Al, Fe, Mn, Ni, Co, Cu, Zn, and Cr) concentration. To distinguish between anthropogenic and natural input of trace metals, enrichment factor (EF), geo-accumulation index (Igeo), and contamination factor (CF) were computed. Further, speciation of metals in selected sub-samples was carried out to understand the bioavailability of metals, and the toxicity of metals to associated biota was assessed using the sediment quality values. The total metal analyses showed higher concentration of Fe, Mn, Ni, Co, Cu, Zn, and Cr in the middle estuarine region which was attributed to metal input from the Lote Parshuram industrial estate located in proximity and adsorption of metals, viz., Ni and Cr onto iron oxide-coated sand particles. EF, Igeo, and CF supported anthropogenic input of metals in the Vashishti estuary. The speciation of metals revealed an increase in Mn concentration in Fe–Mn oxide and exchangeable fractions from bottom to the surface of cores VS-1 and VS-2 respectively, while Co in the exchangeable fraction, and to a lesser extent, Zn in the Fe–Mn oxide fraction showed an increase towards the surface of the core VS-2. These elements exhibited diagenetic remobilization and showed an increase in bioavailability near the surface. Further, comparison of total and bioavailable concentration of metals with sediment quality values indicated risk of Mn and Co to sediment-associated biota.

Environmental availability of ultramafic rock derived trace elements in the fumarolic - geothermal field of Soussaki area, Greece

The geothermal degassing and fumarolic alteration occurring at Soussaki, an area in SE mainland Greece, facilitated a strongly acidic environment which resulted in the serpentinized ultramafic parent rock's severe weathering and a large increase of mobility of trace elements, which may be incorporated in newly formed fumarolic alteration products and secondary clays (Cr – bearing clays). We hypothesized that the fumarolic – hydrothermal alteration of ultramafic parent rock would increase the mobility and availability and would cause the distribution of Cr, Ni, Mn and Co in stream sediments and soils in labile fractions. Stream sediment and surface soil samples were collected from 46 sampling sites and the <1.8 mm grain size fraction was analyzed by Flame Atomic Absorption spectroscopy for the above mentioned elements. Evaluation of geochemical abundance and leachability of the above mentioned elements in each operationally defined geochemical fraction, was conducted by applying multi - acid digestion, single and selective sequential extraction, respectively. Mineralogical composition of the parent rock was determined by means of X – ray diffraction. The stream sediment and soil samples show significant levels of Cr: 1237 mg/kg and 1448 mg/kg, Ni: 1789 mg/kg and 1879 mg/kg, Mn: 875 mg/kg and 904 mg/kg and Co: 114 mg/kg 115 mg/kg content, respectively, in agreement with the high geochemical background of these elements in Soussaki. Our results also indicate that there is a high risk of immediate Ni, Mn and Co mobilization, reaching percentages of 17.8% and 11.3%, 67.7% and 45.2%, 44.2% and 17.6% in the surface adsorbed fraction, in stream sediments and soils, respectively. The stability of significant percentage of all trace elements found in Fe – Mn oxide fractions (Ni > Co > Mn > Cr) is controlled primarily by the Eh/pH system.

Chemical Fractionation of Aluminium in the Sediments of El-Burullus Lagoon of Nile Delta, Egypt

A five step sequential extraction technique, following Tessier’s protocol has been applied to determine the chemical association of aluminium with major sedimentary phases (exchangeable, carbonate, manganese and iron oxides, organic and residual fraction) in four short sediment cores collected from El-Burullus lagoon of the Nile delta, Egypt. This study is a first approach of chemical fractionation of aluminium in one of the protective areas of the Mediterranean Sea of Egypt. The total metal content was also determined. The results of the fractionation study indicated that aluminium was mainly associated with the residual fraction (>95%). The organic and Fe–Mn oxide fractions were the next important phases. The exchangeable and carbonate fractions were less than 1%, limiting its potential toxicity as a pollutant. The geochemical analysis of aluminium forms reflected the lithogenic origin of this metal in the study area.