Mobility Of Trace Metals Research Articles

Changes in mobility of trace metals at the sediment-water-biota interfaces following laboratory drying and reimmersion of a lacustrine sediment.

Alterations in the timing, frequency, and magnitude of water level fluctuations (WLF) in lakes may result in important changes in abiotic parameters that can affect sediment-borne contaminant mobility at the sediment-water-biota interfaces in littoral zones. This study aims to assess the mobility of trace metals (TMs)-Cd, Cr, Cu, Ni, Pb, and Zn-under laboratory-simulated WLF (i.e., drying and reimmersion of sediments) through a three-pronged approach. One surficial sediment was sampled from the shoreline of a large French lake exhibiting an artificially limited WLF. A sample was enriched with a solution of TMs to ensure significant measurements of mobility. The spiked and naturally contaminated sediments were dried and reimmersed. The first approach consisted in measuring the mobility of TMs from the sediment to the water column under resuspensions of particles through leaching tests. The second approach assessed the partitioning of TMs between the different binding forms within the sediments through sequential extraction tests. The last approach tested the changes in TM bioconcentration in organisms exposed to sediment through microcosm assays. The hypothesis was that WLF may increase mobility from the sediment to the water column relative to mobility from the residual to easily mobilizable fractions within the sediments and consequently increase the bioconcentration of less inert trace metals, mostly Cd and Zn. This hypothesis was partly rejected as TM binding forms mainly increased toward the residual fractions within the sediment, especially for Cd and Zn, and bioconcentration mainly decreased following WLF. However, TM concentration increased in the water column when WLF included great resuspension of particles. The study also provides insights into the complex relationships among contaminant mobility to the water column, bioavailability, and bioconcentration, especially in the context of large abiotic disturbances such as WLF. These findings may be useful for further management strategies for WLF-regulated lakes and reservoirs.

Underlying lithology controls trace metal mobilization during redox fluctuations

Redox state fluctuations are a primary mechanism controlling the mobilization of trace metals in soils. However, underlying lithology may modulate the effect that redox fluctuations have on trace metal mobility by influencing soil particle size and mineral composition. To investigate the relationships among trace metal behavior, lithology, and redox state, we subjected surface soils from two intensely weathered soil profiles formed on contrasting lithologies to consecutive, 8-day redox cycles. A suite of metals (Al, Mn, Fe, Ti, Rb, Zr, Nb, Mo, REEs, Pb, Th, U) were quantified in the aqueous phase (<10 nm) and solution (<415 nm, including colloids) from soil slurries. In soil formed on volcaniclastic bedrock with high clay content and a high abundance of short-range-ordered Fe-(oxyhydr)oxides phases (e.g. nano-goethite; quantified by Mössbauer spectroscopy), reducing events and colloidal dynamics drove trace metal mobilization. In contrast, in soil formed on granite bedrock with lower clay content and a low abundance of short-range-ordered Fe-(oxyhydr)oxides phases (nano-goethite and lepidocrocite), overall trace metal mobilization was lower, and mobilization was not predictable from redox state. Molybdenum isotopes were also measured through redox cycles but did not exhibit redox-dependent behavior. This study provides direct evidence that lithology remains an overarching factor governing the characteristics of metal mobility in soils, even after extended and intense chemical weathering and soil development processes.

Trace metals in Northern New England streams: Evaluating the role of road salt across broad spatial scales with synoptic snapshots.

Mobilization of trace metals from soils to surface waters can impact both human and ecosystem health. This study resamples a water sample archive to explore the spatial pattern of streamwater total concentrations of arsenic, cadmium, copper, lead, and zinc and their associations with biogeochemical controls in northern New England. Road deicing appears to result in elevated trace metal concentrations, as trace metal concentrations are strongly related to sodium concentrations and are most elevated when the sodium: chloride ratio is near 1.0 (~halite). Our results are consistent with previous laboratory and field studies that indicate cation exchange as a metal mobilization mechanism when road salt is applied to soils containing metals. This study also documents associations among sodium, chloride, dissolved organic carbon, iron, and metal concentrations, suggesting cation exchange mechanisms related to road deicing are not the only mechanisms that increase trace metal concentrations in surface waters. In addition to cation exchange, this study considers dissolved organic carbon complexation and oxidation-reduction conditions affecting metal mobility from soils in a salt-rich environment. These observations demonstrate that road deicing has the potential to increase streamwater trace metal concentrations across broad spatial scales and increase risks to human and ecosystem health.

Assessment of trace metals in an aquifer with river-groundwater interaction: The influence of colloidal redistribution and porous matrix change on the migration of metals

An aquifer where receives steady lateral recharge from an AMD-polluted river, was chosen to understand the profound influence of the “solid-liquid phase” evolution on the mobility of trace metals. The results showed that the accumulation of trace metals in groundwater was observed near the riparian zone. Zn and Cd almost remained in the “truly dissolved” phase (<3 kDa), whereas Cu and Pb were mainly in the coarse colloid (0.22 μm–30 kDa) and shifted from the coarse colloid to the “truly dissolved” phase along the flow path. The evolution of relatively high dispersive colloids to low dispersive colloids indicated that the Al-rich mineral colloids as the dominance migrated with the groundwater flow path, and flocculated gradually so that the porous matrix was coated by gibbsite. The coating of gibbsite dissociates OH− in acidic environment, resulting in the decreasing negative charge in porous matrix. Thus, the mobility of Cu and Pb was shifted from the colloid-facilitated transport to the co-precipitation with colloids, whereas the mobility of Zn and Cd was changed from the high electrostatic binding to the low electrostatic binding. Numerical simulation also confirmed the varying retardation factor and the total penetration time followed an order of Pb > Cu > Zn > Cd. Therefore, the changes in “two phases” in the aquifer—not only in water phase but also in colloid phase and porous matrix—have a profound influence on metal migration that take place in shallow groundwater where there are close hydraulic connection between river and groundwater.

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”.

Dredging impact on trace metal behavior in a polluted estuary: a discussion about sampling design

Studies involving coastal sediment resuspension have shown that trace metals could be released to the water column due to changes in physical-chemical conditions. Therefore, if environmental agencies adopt screening protocols with insufficient evaluations of contaminant mobilization risks for a given area, the prediction of environmental impacts caused by dredging may be limited. This work evaluates the influence of spatial variation on the geochemical mobility of trace metals (Cd, Cu, Ni, Pb, Zn) after artificial sediment resuspension, using as study case the Iguaçu River estuary (Guanabara Bay, Brazil). The Iguaçu River drains the industrial complex of the metropolitan area of Rio de Janeiro State, besides the presence of agriculture and the input of untreated domestic wastes. Surface estuarine sediments were submitted to resuspension experiments in an open system, during 1h and 24h of agitation on local water. A clear tendency of metals’ solubilization was observed after resuspension, especially considering the dissolved concentrations of Cu (average: 8.0 µg L-1) and Zn (average: 0.9 mg L-1), especially for the samples from the transects 2 and 3. However, evaluations of water quality changes due to sediment resuspension are not requested by the legislation regulating the dredging activities. In the sediments, the results suggested a higher geochemical mobility of Cu, indicated by the massive increase on the bioavailable fraction after resuspension, mainly on the transect number 3, on the river’s mouth. The effects of resuspension were distinct between samples, suggesting that even in a small scale, important differences on metals’ mobility are found. Thus, the combined assessment of changes in metal concentrations in water and in the metal partitioning linked to the solid-phase was demonstrated to be a promising tool for predicting the environmental risks of dredging due to changes in the bioavailability of metals.

The catalytic effect of AQDS as an electron shuttle on Mn(II) oxidation to birnessite on ferrihydrite at circumneutral pH

Abstract Birnessite (δ-MnO2) is the most common manganese (Mn) oxide mineral in soils, sediments, and ocean manganese nodules, and it significantly affects the speciation and mobility of trace metals and organic pollutants. Abiotic oxidation of Mn(II) by dissolved O2 is an important birnessite formation pathway, however, it has rarely been reported at neutral pH due to its very slow oxidation kinetics. Anthraquinone-2, 6-disulfonate (AQDS) is an important electron shuttle in biotic systems and might induce birnessite formation by promoting abiotic Mn(II) oxidation. Herein, the effects of AQDS concentration and types of mineral surfaces on 24 mM Mn(II) oxidation were explored at pH 7.0 using macroscopic and spectroscopic analyses. In the absence of AQDS, birnessite cannot form through the abiotic oxidation of 24 mM Mn(II) unless pH ≥ 8.5. In contrast, birnessite rapidly forms at pH 7.0 in the presence of AQDS, which acts as a catalyst. The catalytic effect of AQDS first increases and then decreases with increasing concentration, and as a “shuttle”, the concentration almost remains constant during Mn(II) oxidation. Additionally, in the absence of ferrihydrite or in the presence of montmorillonite, which is an analogous insulating mineral, AQDS shows a weak catalytic effect on Mn(II) oxidation; thus, no birnessite forms. The mechanisms of Mn(II) oxidation promoted by AQDS and ferrihydrite can be described as AQDS acting as an electronic carrier with semiconductor ferrihydrite as a specific channel facilitating electron transfer between Mn(II) and O2 on its surface. This study provides new evidence that AQDS can transfer electrons in abiotic systems as in biotic systems, leading to efficient Mn(II) oxidation and birnessite formation through an abiotic pathway at circumneutral pH in various geological settings.

Effect assessment of target tissue doses of cadmium and decabrominated diphenyl ether on GSH level in kidneys

Liming is a common practice in the treatment of acidic and metal contaminated soils, aiming at pH regulation, enhancing of the nutrient availability and attenuation of trace metals mobility. Replacement of natural limestone with alternative soil alkalizers found among waste materials represents a step towards sustainable resource management and reduced waste storage. In this study, waste seashells (SW) and red mud (RM) were applied in different doses to the soil sampled in the vicinity of mining and smelting complex. The soil was characterized by acidic reaction (pH 4.93), increased Cu concentration (219.2 mg/kg) and a very low level of P-supply (3.61 mg P2O5/100 g). The study aimed to quantify and compare additive-induced effects onto soil physicochemical properties, the status of macronutrients and distribution of trace metals. Targeted effect on soil pH was achieved with SW dose of 0.3% and RM dose of 2%. RM was found to be a source of available P and gave rise to the available P concentrations in the soil. Medium level of P-supply (15.60 mg P2O5/100 g) was achieved with RM dose of 5%, however, the increase in soil salinity and total trace elements concentrations have become significant adverse effects at such dose. The decrease in the ion-exchangeable content of Cu and other trace metals was in correlation with the increase in soil pH after the treatments. Redistribution of metal cations was mainly directed to carbonate/acid soluble and Fe, Mn-oxide bonded fraction after SW addition. Even though trace metals concentration has increased in the soil after application of the RM, they were principally found in the residual fraction. The results emphasize low amounts of contained trace elements and lower doses for achieving targeted effects on pH and metal mobility as the main benefits of SW treatments. On the other hand, moderate and controlled use of RM may represent multiple benefits in terms of simultaneous pH regulation, P-supply, and reduced trace metals mobility.

Iron speciation at the riverbank surface in wetland and potential impact on the mobility of trace metals

Fe oxyhydroxides in riverbanks and their high binding capacity can be used to hypothesize that riverbanks may act as a “biogeochemical filter” between wetlands and rivers and may constitute a major mechanism in the trapping and flux regulation of chemical elements. Until now, the properties of Fe minerals have been very poorly described in riverbanks. The goals of the present work are to identify Fe speciation in riverbanks where ferric deposits are observed and to determine their impact on the metal behavior (As, Co, Cu, Ni, Pb, Zn, etc.).At the surface, Fe speciation is mainly composed of small poorly crystalline Fe phases, i.e. ferrihydrite (~30%), Fe-OM associations (~40%) as well as crystalline Fe phases, i.e. goethite (~35%). At the subsurface, the Fe distribution is dominated by goethite (~35%) and Fe-mica (~35%), the proportion of which increases at the expense of ferrihydrite and the Fe-OM associations.At the riverbank surface, ferrihydrite and the Fe-OM associations are therefore the main Fe hosting phases in response to (i) the fast Fe(II) oxidation induced by the presence of O2 and (ii) the high amount of OM favoring the formation of nano-phases bound to OM (Fe monomers, polymers and nanoparticles) and preventing mineralogical transformation (ferrihydrite into goethite).During the high-water level period (high flow), a strong erosion of the riverbank transfers these ferric deposits into the river. However, the physicochemical parameters of the river (pH 6.6–7.6 and continuous oxic conditions) do not promote the dissolution of Fe oxyhydroxides and OM. Ferric deposits and the associated trace metals are therefore maintained as colloids/particles and are exported to the outlet. All of the results presented here demonstrate that the ferric deposits trap metals on a seasonal basis and are therefore a key factor in the mobilization of metals during riverbank erosion by river flow.

Metal mobility and mineral transformations driven by bacterial activity in acidic pit lake sediments: evidence from column experiments and sequential extraction

Biogeochemical processes occurring in lake sediments are crucial for element cycling. In acidic pit lakes, they play a major role in acidity neutralization and toxic metal immobilization. However, the relationship between bacterial activity (e.g., iron and sulfate reduction), mineral neoformation, and metal mobility is often difficult to establish and has been rarely reported. The aim of this study was to identify mineral products formed by bacterial activity and their influence on trace metal dynamics during early diagenesis. The study focuses on several acidic pit lakes in SW Spain. We combined chemical analyses of intact sediment cores taken from shallow and deep zones with experimental sediment core incubations aimed at visualizing geochemical and mineralogical transformations occurring in the sediments during early diagenesis. The sediment incubations commenced with a total resuspension and homogenization and lasted for periods of several months. During this time, pore water and overlying water was extracted and analyzed to record geochemical changes. The sediments were also sectioned and chemically analyzed after the experiments to investigate carbon, nutrient, sulfur, iron, and trace metal mobility. Intact sediment cores were analyzed by sequential extraction and differential X-ray diffraction to examine metal speciation and the presence of secondary minerals not detectable by conventional techniques. Shallow sediments are more biogeochemically reactive due to their higher organic carbon content. In columns prepared with these littoral sediments, a sharp pH gradient appeared in the upper 4 cm soon after the beginning of the incubations, suggesting alkalinity generation and concentration of microbial metabolisms (iron and sulfate reduction). This pH gradient provokes the precipitation of Al and leads to the formation of a milky, gelatinous layer in the water/sediment interface. This layer quickly dehydrates and recrystallizes to more stable phases. At the same time, bacterially produced H2S reacts with different metals (Cu, Zn) which are thus immobilized in the sediments as secondary sulfides. However, these two metals are also removed from solution by purely abiotic mechanisms like sorption or coprecipitation. Carbon seems to be the major factor limiting bacterially mediated metal and acidity attenuation in sediments of these acidic pit lakes. Metal immobilization is not a simple process and takes place through a combination of direct precipitation (Al oxyhydroxysulfates, Cu and Zn sulfides) and indirect mechanisms (sorption, coprecipitation, cation exchange). The precipitation of Al is of prime importance for pH buffering and immobilization of other metals (Cu, Zn). This process is not evident in routine chemical analyses of sediment cores, but it can be inferred by a combination of experimental and laboratory techniques such as the ones used here. P and N fertilization of these pit lakes would greatly increase the natural rates of acidity neutralization.

Contrasting sources and mobility of trace metals in recent sediments of western Lake Erie

Abstract Concentrations of the major and trace metals varied considerably in the western basin of Lake Erie, ranging from 0.9 to 25.3 mg/g for aluminum, from 2.9 to 36.5 mg/g for iron, from 6.4 to 74.8 mg/g for calcium, from 1.2 to 13.5 μg/g for cobalt, from 2.8 to 61.6 μg/g for copper, from 2.7 to 83.0 μg/g for lead, from 0.1 to 2.9 μg/g for cadmium, and from 7.1 to 127.3 μg/g for strontium. Distinct patterns of sediment metal variability allowed the identification of two major fluvial sources and some active in-lake biogeochemical processes. The inputs of Sr were largely from the Maumee River, the inputs of Cu, Pb, Cd, and Co were dominated by the Detroit River, and the inputs of Fe and Al were roughly evenly from the two rivers. The removal of Sr and Ca from the water column was mainly through coprecipitation with calcite. In contrast, the transfer of Cu, Pb, Cd, and Co was largely attributed to the removal of fine sediment particles from the Detroit River mouth and adjacent nearshore areas and the deposition of the metals scavenged by settling organic materials in the basin's central deeper areas. The mobility of the trace metals was different during the in-lake mass transfer, with Co being the most mobile and Cd being the least mobile. Furthermore, the trace metal mobility differences have decreased significantly during the past half-century due to a substantial increase in organic matter from eutrophication in the basin.

The impact of preload on the mobilisation of multivalent trace metals in pyrite-rich sediment.

Trace metals occur at various concentrations in all wetlands. Their proliferation, chemical speciation, mobility and bioavailability are dependent on the redox potential (Eh), pH and the presence of organic and inorganic adsorption surfaces and co-precipitating metals. Consequently, changes in these key parameters have the potential to alter the fate of the dominant trace metal species in the sediment. An imposition of preload surcharge is a technique use in geotechnical engineering to improve in the strength and load carrying capacity of waterlogged sediments. The soil strength improvement is effected through the expulsion of porewater from the sediment. The imposition of surcharge over wetland sediments has the potential to create oxygen-deficient condition within the sediment, and cause pH, temperature, redox, EC and salinity changes in the sediment, which would impact on the mobilisation, chemical speciation, mobility and bioavailability of dominant toxic trace metals and their toxicity in the sediment. In the present work, a case study of the impact of preload surcharge on the proliferation, chemical speciation, mobilisation, mobility and bioavailability of arsenic, chromium, cobalt, copper and zinc in a naturally occurring pyrite-rich sediment is presented. The imposition of preload surcharge over the pyrite-rich sediment was accompanied by changes in the redox dynamics of the sediment, with multi-facet impact on the concentration, mobilisation and bioavailability of toxic trace metals, their redox transformation between oxidation states and on the toxicity within and outside the sediment environment.

Distribution of contaminant trace metals inadvertently provided by phosphorus fertilisers: movement, chemical fractions and mass balances in contrasting acidic soils.

The frequent use of phosphorus (P) fertilisers accompanied by nitrogen and potassium sources may lead to a serious long-term environmental issue because of the presence of potentially hazardous trace metals (TM) in P fertilisers and unknown effects on the TM chemical fractions in agricultural soils. A 16-month-long column experiment was conducted to investigate the mobility and chemical forms of Cd, Cu, Cr, Ni, and Zn introduced into a Mollisol and an Andisol through surface incorporation (0-2cm) of triple superphosphate (TSP) fertiliser. The effects of urea and potassium chloride (KCl) applications were investigated as well. After 15 cycles of 300-mm irrigation, TSP addition increased the 4M HNO3 extractable TM concentration in the upper (0-5cm) section of soils. Beyond this depth, metals showed no significant mobility, with minimal leaching losses (< 1.9%, 25-cm depth). The TM chemical forms in the 0-5cm section were significantly (p < 0.01) affected by the soil type and fertilisers addition. Cadmium, Ni, and Zn were the elements which appeared in a larger proportion (up to 30%) in the most labile fraction (KNO3 extractable) in fertilised soils. The impact of urea depended on the nitrification-related changes in soil pH, while fertilisation with KCl tended to increase the KNO3 fraction of most metals probably due to K+ exchange reactions. Chromium remained minimallyaffected by the urea and KCl applications since this contaminant is strongly bound to the less labile solid phases. The low mobility of TM was governed mainly by their interaction with the solid phases rather than by their speciation at soil pH. The mass balance showed that the geochemical processes underwent in time by the P fertiliser increased the amount of TM extracted by the chemical fractionation scheme, therefore the reaction period of TSP with soil particles should be taken into account for evaluating TM availability. Long-term soil fertilisation could inadvertently contribute to an increased concentration and availability of these P fertilisers-born contaminants in the cultivated layer of acidic soils.

Influence of Oxalate on Ni Fate during Fe(II)-Catalyzed Recrystallization of Hematite and Goethite.

During biogeochemical iron cycling at redox interfaces, dissolved Fe(II) induces the recrystallization of Fe(III) oxides. Oxalate and other organic acids promote dissolution of these minerals and may also induce recrystallization. These processes may redistribute trace metals among the mineral bulk, mineral surface, and aqueous solution. However, the impact of interactions among organic acids, dissolved Fe(II), and iron oxide minerals on trace metal fate in such systems is unclear. The present study thus explores the effect of oxalate on Ni release from and incorporation into hematite and goethite in the absence and presence of Fe(II). When Ni is initially structurally incorporated into the iron oxides, both oxalate and dissolved Fe(II) promote the release of Ni to aqueous solution. When both species are present, their effects on Ni release are synergistic at pH 7 but inhibitory at pH 4, indicating that cooperative and competitive interactions vary with pH. In contrast, oxalate suppresses Ni incorporation into goethite and hematite during Fe(II)-induced recrystallization, decreasing the proportion of Ni substituting in a mineral structure by up to 36%. These observations suggest that at redox interfaces oxalate largely enhances trace metal mobility. In such settings, oxalate, and likely other organic acids, may thus enhance micronutrient availability and inhibit contaminant sequestration.

Mobility of heavy metals in sandy soil after application of composts produced from maize straw, sewage sludge and biochar: Discussion of Gondek et al. (2018)

Gondek et al. (2018) investigate the mobility of heavy metals in sandy soil after application of composts produced from maize straw, sewage sludge and biochar. The authors made a little attention to role of the soil properties and soil condition on the metals chemical behavior. In different section of the paper, the authors reported that the content of the metals extracted with water or 1 M NH4NO3 was changed compared to the control treatment affected by the mentioned biosolids. Nowadays, different researches have shown that the trace metals nature have an important role in determining their fate in presence of different treatments. In addition to, organic compounds entered to the soil due to biosolids applications have a duplicate role in trace metals mobility. Therefore, it is needed this facts are considered to interpret the measurements in the original paper. Also, whenever effects of different materials are studied on the metals mobility, the metals status in the plant tissues presents valuable information to the scientists and readers for carefully interpreting the measurements, which it is ignored by the authors.

Trace metal (Cd, Cu, Pb, Zn) fractionation in urban-industrial soils of Ust-Kamenogorsk (Oskemen), Kazakhstan\u2014implications for the assessment of environmental quality

Ust-Kamenogorsk is one of the largest cities and industrial centers in Kazakhstan. Non-ferrous metallurgy (Zn–Pb smelter) has acted as a predominating industrial branch in the city since late 1940s. The industrial plants are situated directly adjacent to the residential area of the city which creates grievous ecotoxicological hazard. In the present paper, we aimed at assessing the trace metal pollution of top soils in Ust-Kamenogorsk and its potential threats to the local population. The top soils were sampled at 10 sites throughout the city center. We determined the physical and chemical properties of soils as well as the contents of Cd, Cu, Pb, and Zn. In addition, the soil samples were subjected to a five-step sequential extraction to ascertain the fractionation of trace metals. On this basis, we calculated the geoaccumulation index (Igeo) and pollution load index (PLI) and assessed bioavailability of the elements. From our data, it emerged that the soils displayed a strong polymetallic pollution. PLI was as high as 33.4. Throughout the city, the trace metal contents exceeded the geochemical background and allowable values for residential, recreational, and institutional areas. The Igeo obtained were 3.7–6.5 for Cd, 1.5–4.7 for Cu, 2.8–5.7 for Pb, and 2.6–4.6 for Zn. The soils in Ust-Kamenogorsk displayed extremely high contamination with Cd, moderate to strong contamination with Pb and Zn, and low to moderate contamination with Cu. Cd and Pb were found to be the most bioavailable elements. The mobility of trace metals in the soils changed in the order Cd > Pb > Zn > Cu.

Reoxidation of estuarine sediments during simulated resuspension events: Effects on nutrient and trace metal mobilisation

Estuarine environments are considered to be nutrient buffer systems as they regulate the delivery of nutrients from rivers to the ocean. In the Humber Estuary (UK) seawater and freshwater mixing during tidal cycles leads to the mobilisation of oxic surface sediments (0–1 cm). However, less frequent seasonal events can also mobilise anoxic subsurface (5–10 cm) sediments, which may have further implications for the estuarine geochemistry. A series of batch experiments were carried out on surface and subsurface sediments taken from along the salinity gradient of the Humber Estuary. The aim was to investigate the geochemical processes driving major element (N, Fe, S, and Mn) redox cycling and trace metal behaviour during simulated resuspension events. The magnitude of major nutrient and metal release was significantly greater during the resuspension of outer estuarine sediments rather than from inner estuarine sediments. When comparing resuspension of surface versus subsurface sediment, only the outer estuary experiments showed significant differences in major nutrient behaviour with sediment depth. In general, any ammonium, manganese and trace metals (Cu and Zn) released during the resuspension experiments were rapidly removed from solution as new sorption sites (i.e. Fe/Mn oxyhydroxides) formed. Therefore Humber estuary sediments showed a scavenging capacity for these dissolved species and hence may act as an ultimate sink for these elements. Due to the larger aerial extent of the outer estuary intertidal mudflats in comparison with the inner estuary area, the mobilisation of the outer estuary sediments (more reducing and richer in sulphides and iron) may have a greater impact on the transport and cycling of nutrients and trace metals. Climate change-associated sea level rise combined with an increasing frequency of major storm events in temperate zones, which are more likely to mobilise deeper sediment regions, will impact the nutrient and metal inputs to the coastal waters, and therefore enhance the likelihood of eutrophication in this environment.

Divergent repartitioning of copper, antimony and phosphorus following thermal transformation of schwertmannite and ferrihydrite

The consequences of fire-induced thermal transformation of poorly crystalline iron minerals on the availability of coprecipitated trace-metals, metalloids and nutrients in fire-prone acid sulfate soils (ASS) landscapes are not well understood. Here, we heat schwertmannite and ferrihydrite containing either coprecipitated copper (Cu), antimony (Sb) or phosphorus (P) at a range of temperatures from 200 °C to 800 °C. Changes in Fe mineralogy and the partitioning of Cu, Sb and P in thermally transformed products were investigated using X-ray diffraction, 57Fe Mössbauer spectroscopy and selective extracts (e.g. water, 1 M MgCl2/0.5 M NaH2PO4/0.5 M NaHCO3, 1 M HCl and aqua regia). The mainly structural incorporation of trace amounts (0.01–0.2%) of Cu, Sb and P into schwertmannite and ferrihydrite negligibly affected initial mineralogy. Irrespective of the presence of coprecipitated Cu, Sb and P, all three types of schwertmannite and ferrihydrite (i.e. Cu, Sb and P-bearing) were transformed to hematite upon heating, although transformation temperatures varied marginally between treatments. All schwertmannites transformed to hematite via a surface adsorbed intermediate iron sulfate oxide phase formed between 400 °C to 700 °C, whereas all ferrihydrites transformed to hematite directly. During heating, the majority of initially structurally incorporated Cu in schwertmannite repartitioned to surface-exchangeable sites, particularly at intermediate temperatures (~300–700 °C). In contrast, Cu in ferrihydrite became stabilized within the structure of hematite. Upon heating both schwertmannite and ferrihydrite, Sb became increasingly stabilized and strongly retained within neoformed hematite. Heating also caused some of the initially structurally incorporated P in schwertmannite and ferrihydrite to repartition to readily exchangeable sites. Our study reveals that thermal transformation of schwertmannite and ferrihydrite can alter and enhance the bioavailability of both Cu (if incorporated in schwertmannite) and P in ASS landscapes, with potential consequences for soil and water quality. In contrast, Sb can be effectively immobilized, likely via isomorphic substitution for Fe(III) in neoformed hematite. The divergent repartitioning behaviour of Cu, P and Sb can be largely explained by interactions between fundamental properties of the trace elements (i.e. atomic radii and valence) and the host Fe mineral(s) structure. Further studies of trace metal(loid) mobility during thermal transformation of common iron minerals would be useful to refine our understanding of the broader consequences of fire for bioavailability of trace metal(loid)s in acid sulfate landscapes.

Assessment of Cr pollution in tributary sediment cores in the Three Gorges Reservoir combining geochemical baseline and in situ DGT

The mobility and transfer of trace metals in sediments are vital to understanding trace metals environmental behavior in water environment. However, as a predominant aquatic carcinogen, an effective method for assessing the release and deposition for Cr at the sediment-water interface (SWI) is still not clearly understood. Here we established a comprehensive methodology to evaluate the release risk of Cr at the SWI combining regional geochemical baseline (RGB) and diffusive gradients in thin films (DGT). Sediment cores and water samples were collected in the two tributaries and mainstream of the Three Gorges Reservoir, which is the world's largest man-made hydroelectric station. Results showed that the calculated Cr carcinogenic risks in surface water did not exceed US EPA maximum recommended level. The RGB of Cr (85.53 ± 14.44 mg/kg) were calculated and the differentials between Cr concentration and RGB in surface sediments showed the average anthropogenic contribution rate was 6.03% and the upstream of Meixi River (MX-S) and mainstream were influenced by anthropogenic activities. The net diffusive flux using DGT showed that Cr in the midstream of Caotang River and MX had the potential to move upwards into the overlying water. Furthermore, combining the results of differential (Cr concentration vs. RGB) and the net flux, MX-S was the only site with a risk of Cr release. To the best of our knowledge, this study is the first attempt to combine RGB and DGT to scientifically assess metal release at SWI and provided a new perspective to comprehensively assess metal pollution in water environment.

Trace metal mobilization by organic soil amendments: insights gained from analyses of solid and solution phase complexation of cadmium, nickel and zinc

The accumulation of Cd in soils worldwide has increased the demand for methods to reduce the metal's plant bioavailability. Organic matter rich soil amendments have been shown to be effective in achieving this. However, it is not known how long these amendments can retain the Cd, and whether dissolved organic matter (DOM) released from them can enhance the metal's mobility in the environment. In this study we sought to test the Cd binding capacity of various organic soil amendments, and evaluate differences in characteristics of the DOM released to see if they can explain the lability of the Cd-DOM complexes. We collected ten organic soil amendments from around New Zealand: five different composts, biosolids from two sources, two types of peat and spent coffee grounds. We characterised the amendments' elemental composition and their ability to bind the Cd. We then selected two composts and two peats for further tests, where we measured the sorption of Ni or Zn by the amendments. We analysed the quality of the extracted DOM from the four amendments using 3D Excitation Emission Matrix analysis, and tested the lability of the metal-DOM complexes using an adapted diffusive gradients in thin-films (DGT) method. We found that composts bound the most Cd and that the emergent Cd-DOM complexes were less labile than those from the peats. Ni-DOM complexes were the least labile. The aromaticity of the extracted DOM appears to be an important factor in determining the lability of Ni complexes, but less so for Zn and Cd.