Sequential Extraction Studies Research Articles

Mechanisms of Cd immobilization in contaminated calcareous soils with different textural classes treated by acid- and base-modified biochars

Acid or base modification of biochars has shown promise for enhancing the immobilization of potentially toxic elements (PTEs) such as cadmium (Cd) in contaminated soils. However, limited information is available on the interaction between soil textural classes and modified biochar application for Cd stabilization in contaminated calcareous soils. Therefore, the objective of the study was to examine the extent of Cd immobilization in contaminated calcareous soils with diverse textural classes, utilizing both acid (HNO3) and alkali (NaOH) modified and unmodified biochars derived from sheep manure and rice husk residues. The modified or unmodified biochars were applied at a rate of 2% (w/w) to Cd-contaminated silty clay loam, loam, and sandy loam soils, followed by a 90-day incubation at field water capacity. Sequential extraction and EDTA-release kinetics studies were used to assess the effect of the treatments on the extent and mechanisms of Cd immobilization. Among the treatments, acid-modified manure biochar was most effective at reducing water soluble and exchangeable Cd fractions (-20.5%), by converting them into metal oxide and organic matter bound fractions. This effectiveness was primarily attributed to the significant increase in surface oxygen functional groups in the acid-modified biochar which could promote Cd complexation. However, the acid-modified manure biochar released more immobilized Cd during EDTA extraction than the base-modified manure biochar, suggesting that EDTA extraction of R-O-Cd complexes was easier than extracting Cd associated with insoluble compounds. This difference was likely due to the acidic pH and lower ash content of the acid-modified biochars compared to the base-modified manure biochars. Additionally, the extent of Cd immobilization was lower in sandy loam soil, highlighting the importance of immobilizing Cd in light-textured soils to prevent its transfer to organisms.

Mobility and fractionation of rare earth elements during black shale weathering: Implications from acid rock drainage and sequential extraction study

Black shale is a type of sedimentary rocks that are enriched in rare earth elements (REEs). It is of both economic importance and environmental significance to understand REE mobility during black shale weathering. The present study approaches to this by analysing REEs in acid rock drainage (ARD) from black shale weathering system, fresh and weathered black shales, soils derived from black shales, and sequential extractants from black shales at Dongping town in Hunan province (China). Results showed that REEs had variable high concentrations in ARD as shown by total REE + Y (∑REY) concentrations from 162 to 4074 (μg/L). REEs in ARD displayed hat-shape NASC-normalized patterns with significant enrichments of middle REEs (MREE) relative to light REEs (LREE) and heavy REEs (HREE), and had significant negative Ce (Ce/Ce⁎ = 0.6) and positive Y (Y/Y⁎ = 1.5) anomalies. MREE enrichment in ARD could be evaluated using MREE/MREE⁎ values, which varied from 1.43 to 1.81 with a mean of 1.65, distinctly higher than those of whole rocks (around 1.0). 1 M HCl extraction results suggested that REEs were integratedly mobilized during shale weathering, while six-step extraction studies identified that REEs in ARD resulted from exchangeable and Fe-oxide fractions with MREE and HREE enrichment in shales respectively. MREE in exchangeable and HREE in Fe-oxide fractions were preferentially released during weathering, as illustrated by plots of MREE/MREE⁎ against HREE/LREE ratios of ARD and six-step extractants. Therefore, geochemical processes for REE mobility during black shale weathering included integrated mobilization and preferential release. Integrated REE mobilization resulted from the dissolution of REE-bearing minerals and oxidation of sulfides. Preferential REE release resulted from acid fluids produced by sulfide oxidation during weathering. Thus, a new model was proposed for interpreting geochemical processes of REE mobility during black shale weathering, and for understanding REE distribution in ARD from natural and anthropogenic systems.

Behavior of trace metals during composting of mixed sewage sludge and tropical green waste: a combined EDTA kinetic and BCR sequential extraction study in New Caledonia.

The aim of the study was to assess the impact of composting on the release dynamics and partitioning of geogenic nickel (Ni), chromium (Cr)and anthropogenic copper (Cu) and zinc (Zn) in a mixture of sewage sludge and green waste in New Caledonia. In contrast to Cu and Zn, total concentrations of Ni and Cr were very high, tenfold the French regulation, due to their sourcing from Ni and Cr enrichedultramafic soils. The novel method used to assess the behavior of trace metals during composting involved combining EDTA kinetic extraction and BCR sequential extraction. BCR extraction revealed marked mobility of Cu and Zn: more than 30% of the total concentration of these trace metals was found in the mobile fractions (F1 + F2) whereas Ni and Cr were mainly found in the residual fraction (F4). Composting increased the proportion of the stable fractions (F3 + F4) of all four trace metals studied. Interestingly, only EDTA kinetic extraction was able to identify the increase in Cr mobility during composting, Cr mobility being driven by the more labile pool (Q1). However, the total mobilizable pool (Q1 + Q2) of Cr remained very low, < 1% of total Cr content. Among the four trace metals studied, only Ni showed significant mobility, the (Q1 + Q2) pool represented almost half the value given in the regulatory guidelines. This suggests possible environmental and ecological risks associated with spreading our type of compost that require further investigation. Beyond New Caledonia, our results also raise the question of the risks in other Ni-rich soils worldwide.

Pollution assessment of antimony in shooting range soils

Soil samples collected from the berm at Thebephatshwa (TAB) shooting range found in Botswana showed variable total concentrations of antimony in the range 38±1 to 283±12 mg/kg. Total antimony concentrations found in the soils were higher than the set regulatory levels by the World Health Organization (36 mg/kg) and the United States Protection Agency (31 mg/kg). The upper berm showed elevated levels of antimony (283±12 mg/kg) due, in part, to the highest density of spent projectiles found in this part of the berm. Sequential extraction studies established that antimony was partitioned mostly in the organic and residual fractions of the soil. Environmental pollution risk assessment based on geoaccumulation index (Igeo), contamination factor (CF) and enrichment factor (EF) indicated all four sections of the berm posed high risk to the environment. The upper berm exhibited extreme pollution from antimony (Igeo ~9), very high contamination (CF ~744) and extreme antimony enrichment (EF ~506) compared to the other three sections studied. Elevated levels of antimony at TAB shooting range call for best shooting range management practices, soil remediation and reclamation methods to be carried out at this shooting range to minimize the mobility and bioavailability of antimony.

Goethite-based carbon foam nanocomposites for concurrently immobilizing arsenic and metals in polluted soils

Although different amendments have been used for the immobilization of metals and metalloids in contaminated soils, in most of them there are still important challenges that need to be faced in order to achieve an optimal result. In this work, a new material based on a carbon foam impregnated with goethite nanoneedles has been developed with the aim of evaluating its effect on the mobility and availability of As, Cd, Cu, Pb and Zn in an industrial soil. For this purpose, leaching, sequential extraction and phytotoxicity studies have been carried out. The results were compared with the same carbon foam without goethite impregnation. When the soil was treated with goethite-based carbon foam nanocomposite, the mobility of metal(loid)s was markedly reduced, with the exception of Zn, which showed moderate immobilization. The presence of acid groups on the surface of the carbon foam, together with a high surface area, led to a strong immobilization of pollutants. Moreover, the modification of the foams using goethite nanoneedles, imply that the novel nanocomposite obtained is effective to remediate simultaneously metal and metalloid-polluted soils, without any relevant effect on soil toxicity.

Mobility and source apportionment of As and heavy metals in the Taehwa River sediment, South Korea: anthropogenic and seasonal effects

The river sediment is a sink for heavy metals flowed into a river from natural and anthropogenic sources. It can be a potential pollutant source in varying environmental conditions. The Taehwa River runs through Ulsan City with different geological terrains and different land uses. Hence, research on the determination of various factors affecting accumulation and mobility changes in heavy metals in the river sediment is important. The present research investigated the mineralogical compositions of the Taewha River sediment in addition to the distribution, speciation, sources, and contamination level of As and heavy metals. The sediment showed different mineralogical changes associated with flowing distance, indicating the influence of country rocks, comprising igneous rocks in the upper stream region and sedimentary rocks in the lower stream region, on mineral composition. The total concentrations of As and heavy metals in the sediment exhibited the order of Zn > Pb > Cr > Cu > Ni > As > Cd. The overall concentrations of As and heavy metals increased in the downstream region, albeit with varying degrees. According to the Environmental Protection Agency guideline for sediment pollution, including the index of pollution intensity (IPOLL) and the potential ecological risk index (RI), the sediment in the sampling stations was discovered to be polluted to varying degrees from anthropogenic activities. An abrupt increase in Pb, Zn, and Cd concentrations was observed at Station 3 in summer and fall, which was linked to the increased clay mineral content caused by seasonal and lithological changes. The sources of this increase can be attributed to a nearby industrial complex or the oxidation of sulfide minerals, which could be related to an abandoned amethyst mine. Sequential extraction studies show that potential toxicity varies for each metal. By comparison, metals such as Cr, Ni, and Cu with higher percentages in exchangeable fractions and fractions bound to carbonates can be highly toxic. The statistical analysis indicates that two groups of metals, one including Zn, Cd, and Pb and another including Cr, Ni, As, and Cu, had distinct origins.

The influence of different antimony (Sb) compounds and ageing on bioavailability and fractionation of antimony in two dissimilar soils.

Assessing the bioavailability of various Sb substances plays a crucial role in human health and the ecological risk assessment of contaminated soils. However, fate, behaviour and bioavailability of different Sb compounds in soils are insufficiently known. Therefore, in this present study, the effects of soil properties and ageing on bioavailability of four different Sb compounds (C8H4K2O12Sb2, Sb2S3, Sb2O3 and Sb2O3 nanoparticles) were evaluated during 120 days ageing time. A black soil (BS) with approximately 12% organic matter (OM) and a red soil (RS) with less than 1% OM were amended with 1000mg Sb kg-1 of different Sb compounds and subjected to single extractions with distilled (DI) water, 2M HNO3, Simplified Bioaccessibility Extraction Test (SBET) and a modified Community Bureau of Reference (BCR) sequential extraction method. The results revealed that there are substantial variations in dissolution rate of various Sb sources, depending upon soil type and Sb compound. The amounts of DI water extractability of Sb during the incubation time varied between <1% and 2%, whereas HNO3 extractable fractions and Sb bioaccessibility at the end of ageing time ranged between about 1%-3% and <1%-9% of the total Sb, with maximum bioaccessibility observed in BS contaminated with C8H4K2O12Sb2. The residual and labile fractions accounted for 77-93% and 0.1-4% of the total Sb, respectively, indicating that Sb is mostly associated with recalcitrant fractions of the soils. The results of single and sequential extraction studies revealed that source of Sb, ageing time and soil properties can greatly affect the bioavailability of Sb in soils. The findings of this research provide a deeper understanding of the potential risks associated with Sb compounds and highlights the role of site-specific considerations for improving the robustness of toxicity guidelines and long-term management of Sb contaminated sites.

Heavy metal pollution and mobility of sediment in Tajum River caused by artisanal gold mining in Banyumas, Central Java, Indonesia.

The heavy metals Cu, Pb, Zn, and Cd in the stream sediment of the Tajum River were studied based on 12 sediment samples obtained from upstream to downstream. The artisanal mining activities in the study area generated mining processing waste (tailing) and are the primary source of heavy metal pollution. The samples were analyzed for metal concentration as well as metal mobility based on sequential extraction analysis. Heavy metal analysis for the concentration of the metals showed that the value of Cu, Pb, Zn, and Cd in sediment samples transcends the mean crust. The change of the heavy metal concentrations in stream sediment between the upstream and downstream areas showed that higher levels were located near mining activities in upstream and that these decreased with distance to downstream. The result of the sequential extraction study revealed that Cu and Pb were more found in the exchangeable and carbonate fraction of about 26% and 24%. Meanwhile, Zn and Cd were present in the Fe-Mn oxide, an organic and residual fraction of about 90% and 85%, respectively. The mobility factor assessment revealed that the heavy metals investigated had an average mobility factor of 25.89%, 23.9%, 14.4 %, and 9.24% for Cu, Pb, Zn, and Cd, respectively. Overall, Zn and Cd in sediment in the study area were less mobile compared with Cu and Pb.

Potential mobilizable Fe from secondary phases of differentially altered subsurface basaltic rock– a sequential extraction study on ICDP site Hawaii

The potential for the mobilization of Fe from secondary phases within subsurface basaltic rocks of the Hawaii Scientific Drilling Project Phase2 (HSDP2) drill core was investigated to elucidate the possible contribution of volcanic islands to the Fe budget of nearby ocean surface waters. Rock specific parameters governing Fe mobilization, such as Fe redox state, specific surface area (SSA), and connected porosity were determined. A four-step sequential extraction procedure using solutions with increasing strength of the extractants was applied to characterize different states of chemical bonding of Fe in secondary phases of the basaltic rocks, a controlling parameter for its release to oceanic water. The sequential extraction results were then used as a measure for the reactivity of secondary Fe-bearing phases and the mobilizable Fe from these rocks. Basaltic rocks with different degrees of weathering showed elevated Fe(III) contents up to 58% total Fe as Fe(III), compared to 11–18% in fresh basalts. SSAs increased with depth, with maximum values of 70 m2/g observed for hyaloclastites. Both parameters depended mainly on the alteration state of the basalt, which was more strongly affected by the fluid chemistry (freshwater ↔ seawater) than by the age of the rocks. The sequential extractions revealed the presence of highly reactive secondary Fe-bearing phases in submarine rocks exposed to seawater whereas observations for rocks altered in freshwater point to better crystallized phases with lower mobilizable Fe contents. In seawater, aging of secondary Fe-bearing phases was most probably suppressed by the adsorption of silica and multivalent anions. Comparing different types of rock, hyaloclastites and pillow basalts showed the highest mobilizable Fe with up to 19% and 16%, respectively, of the total Fe of the bulk rock. The potential for high amounts of mobilizable Fe from basaltic rocks altered under seawater dominated conditions suggests that the submarine part of volcanic ocean islands represent an underestimated source of Fe supply to ocean surface waters.

Monsoonal paddy cultivation with phase-wise arsenic distribution in exposed and control sites of West Bengal, alongside its assimilation in rice grain

The present study mainly deals with monsoonal paddy farming with respect to its phase-wise arsenic (As) accumulation and distribution throughout cultivation in As exposed sites and control areas of West Bengal for two consecutive years, 2017 and 2018. Arsenic uptake in paddy depends on the watering pattern with the help of groundwater (Madhusudhankati: 171 μg/l, Teghoria: 493 μg/l in Gaighata and Pingla: 10 μg/l in Medinipur), soil As phase-wise movement with its enrichment pattern and the variation of rainfall. Arsenic mobility is the highest in root and decreases with height of a plant. However, the synergistic effect of groundwater and rainwater makes a diffused approach to the nature of As flow in plants, because rainwater has a pivotal role in diluting the As content available for translocation. Reproductive phase accumulates maximum As compared to vegetative and ripening phases. Sequential extraction and SEM studies re-confirm no possibility of iron (Fe) plaque formation in root soils which sequestered As. Finally, we conclude that monsoonal cultivation provides least As enriched grain (exposed area: 350 μg/kg, control area: 224 μg/kg) irrespective of the variety of cultivar and area of cultivation, which amounts to one-third of pre-monsoonal grain (1120 μg/kg) and so, it is much safer for consumption with respect to As and micro-nutrient status.

Phosphorus pools in Al and Fe-based water treatment residuals (WTRs) following mixing with agro-wastewater — A sequential extraction study

Abstract Phosphorus can be removed successfully from dairy wastewater using Al- or Fe-water treatment residuals (Al-WTR, Fe-WTR). Understanding the characteristics of P-sorbing pools can facilitate reuse of the newly formed organic composites (WW-Al/O-WTR, WW-Fe/O-WTR) as fertilizers. Phosphorus fractionation in heterogenic materials requires a specific composition of chemical extractants. The SEDEX protocol suited the Fe-WTR, but the Al-WTR required a modified protocol that focused on the Al-bound pool. Both fractionation protocols express similar pools consisting of the labile-, the major tri-valent (hydr)oxides-, moderately- and strongly Ca associated-P pools. The modified Al-WTR sequential P extraction protocol allows for differentiation between inorganic P (Pi) versus organic P pools, including most labile P, P bound onto Al (hydr)oxide surfaces, Fe (hydr)oxide- and humic substances (HS)-bound, moderately labile Ca-bound, strongly Ca-bound, and residual occluded P. The strongly Ca-bound P constituted 65% of P in the original Al-WTR. Following mixing with dairy wastewater, this pool became 40% of the P in WW-Al/O-WTR, while surface Al (hydr)oxide and moderately labile Ca fractions became larger (33% and 19% Pi, respectively). Organic P was mainly associated with the moderately labile Ca-bound (68%) fraction, and only 25% was strongly bound to Fe and HS. The predominating P pool on Fe-WTR was Fe (hydr)oxides (61%), with a similar fraction of labile and CaCO3 bound P (about 16%). Mixing Fe-WTR with dairy wastewater significantly increased P bound to Fe (hydr)oxides and labile P, and decreased P pools associated with Ca (ca. 62, 30 and

Behavior of Ag species in presence of aquatic sediment minerals – In context of aquatic environmental safety

In recent years, there has been a growth in the number of products containing Ag nanoparticles (AgNPs) in many areas and their use suggests that the water-soil environment may be exposed to the contaminant with different Ag species.Therefore, the sorption of two Ag forms (i.e. Ag(I) ions and nanoparticles – AgNPs) on clay minerals (montmorillonite and kaolinite) and iron (oxyhydr)oxides (ferrihydrite) as a function of solution:mineral ratio (100:1, 250:1, 500:1), solution pH (3.0, 5.5 and 7.0) and initial Ag concentration (0.1–100 mg/dm3) was studied using batch method. In addition the binding strength/mobility of the bonded Ag species was researched. The results show a great sorption potential of clay minerals for both Ag forms and lower sorption capacity of ferrihydrite, in particular for Ag(I) ions. The maximum sorption capacities of montmorillonite, kaolinite and ferrihydrite estimated from three-parameter isotherm model of Sips were 94.39 mg/g, 117.8 mg/g and 26.48 mg/g for AgNPs and 17.92 mg/g, 21.14 mg/g and 3.072 mg/g for Ag(I) ions, respectively. Aggregation process plays an important role in sorption and mobility of AgNPs.The sequential extraction study indicated different binding mechanisms of the Ag forms onto the clay minerals and ferrihydrite, which depended on the active sites of minerals as well as the Ag species nature in the solution. Ag(I) was weakly bound by clay minerals but presence of iron (oxyhydr)oxides decreased the Ag(I) mobility and bioavailability. On the other hand, AgNPs bound with the active centers of minerals in a very strong way and were not able to release into water.The study of the binding of Ag forms by clay minerals and (oxyhydr)oxides allows to determine the influence of their physicochemical and structural properties, including e.g. pore size on Ag sorption. These results allow these properties to be taken into account in the study of environmental samples, including waters and soils.Moreover, the results showed that in the study of behavior of Ag forms in contact with the minerals, in addition to the sorption capacity, the susceptibility to their release is very important.Studies on sorption/desorption of AgNPs and Ag(I) ions as a form of oxidation of AgNPs is important for understanding the transport and fate of the Ag species in soil, sediments and surface water because of different their behavior in contact with the minerals.

Sequential extraction studies on the river Tisa sediments for the assessment of the metal pollution

The sequential extraction procedure was applied for partitioning of metals in river sediments collected along the course of the river Tisa (Serbia). Eight elements (Sb, Sn, As, Cd, Cu, Hg, Pb and Zn) from twenty-one sampling site were analyzed using the modified BCR sequential extraction procedure in combination with ICP-OES. The results of sequential extraction, statistical analyses and calculation of EF and lithogenic and anthro?pogenic ratio of metals are similar. In the river Tisa sediments Sn, Cd, Hg, Pb and Zn are of anthropogenic origin, while As, Cu and Sb are of lithogenic and anthropogenic origin. The sediments from the river Tisa show high risk for Cd, medium risk for Hg and Zn, low risk for Sn, As, Cu and Pb, whereas Sb does not show the risk for the aquatic environment.

An assessment of pH-dependent release and mobility of heavy metals from metallurgical slag

The paper presents the results obtained in pHstat leaching test and assesses the influence of pH changes and occurring processes on the release of heavy metals (Cd, Ni, Crtotal, Pb, Cu and Zn) from metallurgical slag in a zinc smelter. Additionally, the analysis of the potential maximum amount of element available for leaching and releasing in the batch leaching test was carried out. All the results of the leaching tests were compared with the total content of heavy metals in the material. In order to evaluate the chemical forms of elements, a sequential extraction study was also carried out. On the basis of test results obtained in pHstat test, a strong dependence of heavy metals leaching on the pH was found. The highest concentrations of the analysed elements were observed in acidic environment. For most metals, except for lead, an increase in the pH of the solution caused a decrease in their concentration. Lead showed an upward trend of release under alkaline conditions. A sharp increase of copper leaching at pH 10.5 was also observed. Based on the results of the study, cadmium can be considered the most mobile element from metallurgical slag. Chromium indicated the lowest degree of release.

Comparing Schwertmannite and Hydrobasaluminite Dissolution in Ammonium Oxalate (pH 3.0): Implications for Metal Speciation Studies by Sequential Extraction

The “poorly crystalline iron oxy-hydroxides” are one of the most reactive and environmentally important fractions in soils and sediments due to the association of many toxic elements associated with these minerals. The metal content of this fraction in sequential extraction procedures is usually evaluated by dissolution in ammonium oxalate ([NH4]2C2O4·H2O) at pH 3.0 and 25 °C. Such chemical treatment, however, may also dissolve other mineral phases of comparable reactivity, which can lead to wrong interpretations of mineral carriers for specific metals. In this study, we compare the dissolution kinetics of schwertmannite and hydrobasaluminite, two minerals of comparable crystallinity and reactivity that play a major role in the mobility of many trace metals in waters and sediments affected by acid mine drainage (AMD). We first synthesized these two minerals in the laboratory by partial neutralization of two different metal-rich mine waters, and then we applied the standard protocol of ammonium oxalate dissolution to different specimens; the solutions were periodically sampled at intervals of 2, 5, 10, 15, 30 and 60 min to compare (i) the kinetics of mineral dissolution, and (ii) the metals released during dissolution of these two minerals. The results indicate a very similar kinetics of mineral dissolution, though hydrobasaluminite exhibited a faster rate. Some toxic elements such as As, Cr or V were clearly bonded to schwertmannite, while many others such as Cu, Zn, Si, Co, Ni and Y were clearly linked to hydrobasaluminite. These results suggest that studies linking the mobility of many elements with the Fe cycle in AMD-affected soils and sediments could be inaccurate, since these elements could actually be associated with Al minerals of poor crystallinity. The step of ammonium oxalate dissolution in sequential extraction studies should be best described with a more general term such as “low-crystallinity oxy-hydroxides”.

Vertical distribution of major ore-forming elements and the speciation in the semiarid system above the concealed Baiyinnuoer Pb-Zn deposit in inner Mongolia, China

The concealed (&gt;80 m) Baiyinnuoer Pb-Zn deposit in Inner Mongolia is a typical skarn deposit in North China and has been studied to improve geochemical exploration within the area. Two vertical soil profiles were studied in order to evaluate the vertical geochemical distribution patterns within the residual soil associated with this deposit. Soil Profile #6 is located above the Pb-Zn orebody whereas Profile #8 is located away from this deposit. To determine the dynamics of the vertical geochemical distribution patterns, concentrations and species of nine elements in samples of six different size fractions were used. The distribution patterns of all the nine elements along Profile #6 display a similar trend of lower concentrations in both the topsoil and moderately-weathered bedrock layers but higher concentrations in the residual subsoil layer, showing an inverted ‘C-shape’. The normalized concentrations (using Fe) of elements and the normalized enrichment factors also follow the same distribution patterns. A sequential extraction study of the soil showed that ore-forming and pathfinder elements were dominantly related to humic acid, Fe-Mn oxides and residual fractions. Based on the results, the recommended soil sampling depth for detecting surficial geochemical anomalies in this and similar semi-arid and thickly covered area is 2–3 m. Furthermore, Hg, Sb, As, Cu, Pb, Zn, Mn and Bi appear to be important indicators for geochemical exploration of Pb-Zn deposits. The research approach and results of this study are useful for evaluating mineral resources in similar covered areas through surface geochemical soil surveys as well as for providing insights to the dynamics of vertical geochemical patterns in soil from concealed Pb-Zn deposits.

Sequential extraction studies of Cu, Cd and U compounds from Gibbsite – bearing shale material, Abu Thor area, Southwestern Sinai, Egypt.

Sequential extraction studies of Cu, Cd and U compounds from Gibbsite – bearing shale material, Abu Thor area, Southwestern Sinai, Egypt.

Effect of pH on transport and transformation of Cu-sediment complexes in mangrove systems

Impact of pH variation of overlying water column on transport and transformation of Cu-sediment complexes in the bottom mangrove sediments was investigated by using different metal extraction studies. The total Cu concentration in the studied sediments varied from ~64 ± 1 to 78 ± 2 mg·kg−1. The sequential extraction study showed that a major part of the sedimentary Cu (85–90% of the total sedimentary Cu) was present within the structure of the sediments with minimum mobility and bioavailability. The redistribution of non-residual Cu among the different binding phases of the sediments was observed at different pH. It was found that Cu shifted from the different non-residual binding phases to the organic binding phase of the sediments at higher pH. Partial leaching of sedimentary Cu-SOM complexes (with increasing stability as determined by kinetic extraction study) was observed at higher pH. This study infers that increase in pH of overlying water column may release Cu-SOM complexes and increase the mobility of Cu-complexes in mangrove systems.

Hazardous elements and amorphous nanoparticles in historical estuary coal mining area

In Brazil, intense coal exploitation activities have led to environmental deterioration, including soil mortification, water contamination, loss of ecosystem, and atmospheric contamination. In addition, considerable quantities of sulfur-rich residues are left behind in the mining area; these residues pose grave environmental issues as they undergo sulfide oxidation reactions. When sulfur oxides come in contact with water, extreme acid leachate is produced with great proportions of sulfate, and hazardous elements (HEs), which are identified as coal drainage (CMD). CMD is an environmental pollution challenge, particularly in countries with historic or active coal mines. To prevent CMD formation or its migration, the source must be controlled; however, this may not be feasible at many locations. In such scenarios, the mine water should be collected, treated, and discharged. In this study, data from 2005 to 2010 was gathered on the geochemistry of 11 CMD discharges from ten different mines. There are several concerns and questions on the formation of nanominerals in mine acid drainage and on their reactions and interfaces. The detailed mineralogical and geochemical data presented in this paper were derived from previous studies on the coal mine areas in Brazil. Oxyhydroxides, sulfates, and nanoparticles in these areas possibly go through structural transformations depending on their size and formation conditions. The geochemistry of Fe-precipitates (such as jarosite, goethite, and hematite) existent in the CMD-generating coal areas and those that could be considered as a potential source of hazardous elements (HEs) (e.g., Cr) were also studied because these precipitates are relatively stable in extremely low pH conditions. To simplify and improve poorly ordered iron, strontium, and aluminum phase characterization, field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), micro-Raman spectroscopy, and X-ray diffraction (XRD) and sequential extraction (SE) studies were executed on a set CMD samples from the Brazilian mines. This study aimed to investigate the role of both nanomineral and amorphous phase distribution throughout the reactive coal cleaning rejects profile and HEs removal from the water mine to provide holistic insights on the ecological risks posed by HEs, nanominerals, amorphous phases, and to assess sediments in complex environments such as estuaries.

Kinetic and equilibrium based fractionation study of Pb in continental shelf sediment of India

Two independent analytical methods (kinetic and sequential extraction protocols) were used to understand the distribution, stability, and lability of Pb-sediment complexes in Indian continental shelf. The concentrations of sedimentary Pb varied from 12.0±0.6 to 30.4±0.1mg·kg−1 and 15.9±0.3 to 36.7±0.4mg·kg−1 in the western and eastern shelf of India respectively. The kinetic extraction study showed that higher proportion of labile Pb-complexes were present in the eastern shelf sediments (~24% of total Pb) than the western shelf sediments (~14% of total Pb). The sedimentary organic matter was found to regulate lability of sedimentary Pb complexes. The sequential extraction study suggested that Fe/Mn oxyhydroxide were the primary hosting phase for labile Pb complexes. This study showed that water soluble, exchangeable, carbonate/bicarbonate-Pb complexes in the sediments was labile. This study provides a better physicochemical description of stability or lability of Pb complexes in the coastal sediment of India.