Solubility Of Trace Elements Research Articles

The Biogeochemistry of Electroactive Humic Substances and Its Connection to Iron Chemistry in the North East Atlantic and the Western Mediterranean Sea

AbstractWe present the zonal distribution of electroactive humic‐like substances (eHS) along a section from Offshore Portugal in the North East Atlantic to the Sicily Channel in the Mediterranean Sea. The concentrations were normalized to Suwannee River Fulvic Acid and ranged from 11 μg/L to 81 μg/L. The vertical distributions were typical of those previously reported for dissolved organic carbon in the Mediterranean Sea. High eHS concentrations were measured in surface water and concentrations decreased with depth before increasing again toward benthic maxima measured at some stations. We estimate that eHS represented a relatively small fraction of the natural organic matter in the Mediterranean Sea (2–5%) but considering their important role in the complexation and the solubility of key trace elements (e.g., iron and copper), the eHS cycle could influence the entire biogeochemistry of these marine systems. We identified key processes controlling the concentration of eHS. While biologically mediated production was the major source of eHS, riverine and rain inputs as well as sediment release were also likely external sources. Low eHS concentrations at subsurface depths pointed to photodegradation as a possible sink of eHS, but degradation by heterotrophic bacteria seemed to be the main sink in the deep sea. Finally, we found a positive correlation between dissolved iron and eHS concentrations. Estimation of eHS contribution to iron binding ligand concentrations indicates the complexation of iron by eHS in the Mediterranean Sea. These observations suggest links between the cycles of eHS and iron in the Mediterranean Sea.

Concentration, Solubility, and Dry Deposition Flux of Trace Elements in Fine and Coarse Particles in Qingdao During Summer

PM2.5 and total suspended particulate (TSP) samples were synchronously collected in Qingdao from June to July 2016. The total and water-soluble concentrations of 12 trace elements in these samples were analyzed to investigate their distribution characteristics in fine and coarse particles as well as their dry deposition fluxes. The results showed that the total mass concentrations of Al, Fe, Sr, Mn, and Ba, which are expected to mainly originate from crustal sources, were generally distributed in the coarse particles, and the part mass in the coarse mode accounted for 55%-60% of their total concentrations. Cr, Ni, V, Zn, Pb, As, and Cd, which mainly originate from anthropogenic contributors, generally existed in fine particles where the part mass accounted for 65%-85% of their total concentrations. The soluble mass concentrations of trace elements, whether from crustal or anthropogenic sources, were mainly distributed in the fine particles. The proportions of Al, Fe, Mn, and Ba in soluble mass concentration existing in the fine particles were 50%-80% and 70%-90% for Cr, Ni, V, Zn, Pb, As, and Cd. The solubility of trace elements was higher in fine particles than in coarse particles. The soluble concentrations of trace elements exhibited a positive correlation with acid compounds, and the solubility exhibited a negative correlation with pH in the fine particles, implying that acidification processes play a key role in determining the solubility of trace elements in fine particles. The soluble fractions in the total dry deposition flux of Al and Fe were only 1%-2%; that of Sr, Ba, Cr, and Pb were about 30%-40%; and that of Mn, Ni, V, Zn, As, and Cd were about 50%-60%. The atmospheric deposition of soluble Fe supported phytoplankton carbon production of (194±150) mg·(m2·d)-1, contributing about 10% of the primary productivity in the Yellow Sea.

Long term insight into biodiversity of a smelter wasteland reclaimed with biosolids and by-product lime

Smelter wastelands containing high amounts of zinc, lead, cadmium, and arsenic constitute a major problem worldwide. Serious hazards for human health and ecosystem functioning are related to a lack of vegetative cover, causing fugitive dust fluxes, runoff and leaching of metals, affecting post-industrial ecosystems, often in heavily populated areas. Previous studies demonstrated the short term effectiveness of assisted phytostabilisation of zinc and lead smelter slags, using biosolids and liming. However, a long term persistence of plant communities introduced for remediation and risk reduction has not been adequately evaluated.The work was aimed at characterising trace element solubility, plant and microbial communities of the top layer of the reclaimed zinc and lead smelter waste heaps in Piekary Slaskie, Poland, 20 years after the treatment and revegetation. The surface layer of the waste heaps treated with various rates of biosolids and the by-product lime was sampled for measuring chemical and biochemical parameters, which are indicative for metals bioavailability as well as for microorganisms activity. Microbial processes were characterised by enzyme activities, abundance of specific groups of microorganisms and identification of N fixing bacteria. Plant communities of the area were characterised by a percent coverage of the surface and by a composition of plant species and plant diversity. The study provides a strong evidence that the implemented remediation approach enables a sustainable functioning of the ecosystem established on the toxic waste heaps. Enzyme activities and the count of various groups of microorganisms were the highest in areas treated with both biosolids and lime, regardless their rates. A high plant species diversity and microbial activities are sustainable after almost two decades from the treatment, which is indicative of a strong resistance of the established ecosystem to a metal stress and a poor physical quality of the anthropogenic soil formed by the treatment.

Regional trends in the fractional solubility of Fe and other metals from North Atlantic aerosols (GEOTRACES cruises GA01 and GA03) following a two-stage leach

Abstract. The fractional solubility of aerosol-derived trace elements deposited to the ocean surface is a key parameter of many marine biogeochemical models. Despite this, it is currently poorly constrained, in part due to the complex interplay between the various processes that govern the solubilisation of aerosol trace elements. In this study, we used a sequential two-stage leach to investigate the regional variability in fractional solubility of a suite of aerosol trace elements (Al, Ti, Fe, Mn, Co, Ni, Cu, Zn, Cd, and Pb) from samples collected during three GEOTRACES cruises to the North Atlantic Ocean (GA01, GA03-2010, and GA03-2011). We present aerosol trace element solubility data from two sequential leaches that provide a solubility window, covering a conservative lower limit to an upper limit, the maximum potentially soluble fraction, and discuss why this upper limit of solubility could be used as a proxy for the bioavailable fraction in some regions. Regardless of the leaching solution used in this study (mild versus strong leach), the most heavily loaded samples generally had the lowest solubility. However, there were exceptions. Manganese fractional solubility was relatively uniform across the full range of atmospheric loading (32 ± 13 and 49 ± 13 % for ultra high-purity water and 25 % acetic acid leaches, respectively). This is consistent with other marine aerosol studies. Zinc and Cd fractional solubility also appeared to be independent of atmospheric loading. Although the average fractional solubilities of Zn and Cd (37 ± 28 and 55 ± 30 % for Zn and 39 ± 23 and 58 ± 26 % for Cd, for ultra high-purity water and 25 % acetic acid leaches, respectively) were similar to Mn, the range was greater, with several samples being 100 % soluble after the second leach. Finally, as the objective of this study was to investigate the regional variability in TE solubility, the samples were grouped according to air mass back trajectories (AMBTs). However, we conclude that AMBTs are not sufficiently discriminating to identify the aerosol sources or the potential effects of atmospheric processing on the physicochemical composition and solubility of the aerosols.

Concentrations and Solubility of Trace Elements in Atmospheric Precipitation in Qingdao

Thirty-five atmospheric precipitation samples were collected at an urban site in Qingdao from June 2016 to May 2017. The total and soluble concentrations of eight trace elements in the samples were determined, and the variable characteristics of the concentrations and solubility of trace elements, as well as the factors affecting the solubility of trace elements in atmospheric precipitation, have been discussed. Based on the overall data, the total concentrations of the trace elements were found to be in the order Al > Fe > Zn > Mn > Ba > Pb > Sr > V, but the soluble concentrations of the trace elements were in the order Zn > Al > Mn > Fe > Ba > Sr > Pb > V. Solubility was about 5% for the crustal elements Al and Fe, and the solubility of the elements affected by anthropogenic sources was relatively higher, 10%-40% for Pb and Ba, 20%-60% for Mn and Sr, and nearly 55% for Zn and V. The total and soluble concentrations of the trace elements were higher in winter and spring than in summer and autumn, but element solubility in spring was the highest. During continuous rainfall, the total concentrations of trace elements in precipitation decreased appreciably, but the variation trend of the solubility of trace elements was not consistent during the different rainfall processes. The variation in pH was the main factor controlling the solubility of trace elements in precipitation.

Multiple oxidation state trace elements in suboxic waters off Peru: In situ redox processes and advective/diffusive horizontal transport

Abstract Oxygen minimum zones (OMZs), where the concentrations of oxygen are at analytical detection limits, but sulfate reduction is not occurring, are termed suboxic and typically nitrate serves as the terminal electron acceptor for heterotrophic respiration. Such respiration is highest near the top of OMZs where maxima in nitrite and other redox active species are observed. Within OMZs, the availability of free electrons for reduction reactions (pe) can range from − 2 to 10 and at thermodynamic equilibrium could control the oxidation states of essential trace elements like iron and toxic ones like arsenic. In turn, this oxidation/reduction speciation affects trace element solubility and bioavailability , thus controlling their reactivity and transport. Field observations and mesoscale models demonstrate the increasing areal extent of oxygen minimum zones, but whether this in turn affects trace element cycling and fluxes remains to be verified. From current observations, it is difficult to determine the relative importance of in situ processes and lateral transport from boundaries to trace elements' redox cycling, which are typically highly redox- and biologically-active in these systems. Such processes could lead to the co-occurrence of redox species that are not controlled by a unique pe. In order to evaluate the effects of in situ redox processes versus advective/diffusive transport on trace elements, the cycling of nitrate/nitrite, iodate/iodide, Fe(II), As(III)/As(V), and hydrogen sulfide was examined in the low oxygen waters off the Peru shelf to the open South Pacific Ocean during the US GEOTRACES GP16 transect in 2013. Nitrite, Fe(II), and iodide were observed from the shelf to 95° W, while reduced forms of sulfur and arsenic were absent. Maxima in nitrite, Fe(II) and iodide were coincident, indicating the utilization of Fe(III), iodate and nitrate as terminal electron acceptors was possible. For iron, this finding was unexpected with regards to thermodynamics. However, closer inspection combined with advective/diffusive modeling of water column data and 228Ra-based flux calculations, showed that benthic redox processes, coupled with westward isopycnal transport, influenced the chemical composition and redox speciation within the upper OMZ well offshore. This horizontal transport contributed to the coexistence of Fe(II) with nitrate, indicating that Fe redox chemistry is under kinetic, rather than thermodynamic, control.

Determination of water-soluble elements in PM2.5, PM10, and PM2.5-10 collected in the surroundings of power plants

The analysis reported in this study was performed to characterize the concentrations and water-soluble content of trace elements (As, Cd, Co, Cr, Hg, Mn, Ni, Pb, Sb and Se) in PM2.5, PM10 and PM2.5-10 samples collected in the surroundings of power plants in southern Poland. The solubility of trace elements bound to PM2.5 and PM10 was higher than for PM2.5-10, and in most cases, significant differences were revealed in the relative percentage concentrations of the water-soluble fractions. The occurrence of Cd, Cr, Mn, Ni, Pb and Se in first PCA (Principal Component Analysis) factor (PC1) – indicate coal combustion processes as the potential source of these elements. Other factors indicate two further anthropogenic sources: the resuspension of road dust due to vehicular activities and waste burning in domestic sources – factor (PC2), and, soil dust sources affected by fugitive dust from the mining processes and unpaved roads, as well as transportation and deposition of coal –factor (PC3).

Distributions of lithium-ion and nickel-metal hydride battery elements in copper converting

Waste batteries, such as rechargeable Lithium-ion and Nickel-Metal Hydride batteries, are important secondary raw materials. They contain considerable amounts of valuable metals, like Ni, Co, Cu, Mn, rare earth elements (REE) and Li. Recovery of these metals from waste streams is vital to decrease the primary production, increase resource efficiency and mitigate against future supply risk. Especially, as the consumption of rechargeable batteries is estimated to rise significantly and the current recovery rates are extremely low. Pyrometallurgical processing, such as secondary copper smelting, offers potentially an effective recovery route for a number of the key elements. Based on the fact that different trace elements have characteristic thermodynamic properties, they distribute in different material streams during pyrometallurgical processing, i.e. metal, matte, slag, magnetite, with different ratios. In particular, solubilities of trace elements in the primary magnetite phase have been properly investigated for the first time. Furthermore, fundamental data about the distributions of Li, Mn, and REE's in copper processing are also subject of speculation. The present study ascertains the distributions and deportments of battery elements during copper converting, between temperatures 1200 and 1275 °C. The thermodynamic data measured as a part of this study will provide basics and solid guidelines for the recovery of the studied trace elements in the industrial copper smelting and converting processes.

Effect of waste mixed with biochar as soil amendment on trace element solubility in a mine soil

Abandoned mining sites often cause contamination of surface and subsurface waters. A 3-month pot experiment was performed to evaluate the influence of waste mixed with biochar as a soil amendment on a series of chemical characteristics and trace element solubility in a mine soil. Trace element concentrations were measured in pore water of the mine soil reclaimed with different proportions of waste-biochar amendment (20, 40, 80 and 100%) and grown with <em>Brassica juncea</em>. The results showed that amendment application improved soil conditions such as pH, total carbon, dissolved organic carbon, total nitrogen, and strongly reduced the concentration of Al (99.99%), Co (99.95%), Cu (99.97%), Fe (99.79%) and Ni (99.91%) in pore water, compared to the unamended soils. Waste and biochar also promoted the establishment of <em>B. juncea</em> in the mine soil. These results highlight the importance of mitigating the impacts from abandoned mines sites on water quality. The use of waste and biochar as soil amendment combined with <em>B. juncea</em> plants was effective in reducing metal concentrations in pore water and the associated toxicity risk.

Acid solubility and affinities of trace elements in the high-Ge coals from Wulantuga (Inner Mongolia) and Lincang (Yunnan Province), China

The Wulantuga and Lincang Ge ore deposits are both considered world-class, coal-hosted germanium deposits. Previous studies have suggested that the abnormally enriched trace elements (including Ge, W, As, Sb, Be, U, and Nb) and rare earth elements and Y (REY) in the Wulantuga and/or Lincang high-Ge coals are associated with organic matter to varying degrees.Unlike previous studies that have used untreated bulk coal for trace element analyses, element affinities in this study were evaluated based on a comparison of their concentrations before and after HCl-HF treatment. Thirteen bench samples from Wulantuga and Lincang were micronized to ~3μm using a fluid energy mill to ensure effective exposure of mineral matter to acids during subsequent HCl-HF demineralization. Trace element concentrations of both micronized coals and micronized-demineralized coals were determined using ICP-MS. Separately, a multi-stage acid leaching analysis was conducted to investigate the individual effects of HCl, HF, and HNO3 on trace element content.Most trace elements that are widely considered to have varying degrees of organic affinity in the Wulantuga and/or Lincang high-Ge coals, including Ge, W, As, Sb, Be, U, Nb, and REY, can be removed to a large extent by thorough HCl-HF leaching, which suggests that if these elements do have an organic association they are held only weakly by the organics. In addition, multi-stage acid leaching results show that HCl is highly effective in the removal of W, As, and REY in the Wulantuga high-Ge coal and As, Be, U, and REY in the Lincang high-Ge coal, whereas HF contributes most to the removal of Ge and Sb in the Wulantuga coal, and Ge, W, Sb, and Nb in the Lincang coal. The highest Ge contents are seen in those lignites that have the highest huminite contents.The most likely explanation for the observations made in this study is that the abnormally enriched trace elements (especially Ge) in the Wulantuga and Lincang high-Ge coals are weakly bonded to organic matter, possibly occurring in the form of chelates, thus allowing them to be removed by HCl-HF. Alternatively, these elements may be associated with fine-grained minerals (or poorly crystalline mineraloids or non-mineral inorganics) that are closely associated with organic matter but are difficult to detect.

Evolution of trace elements in the planetary boundary layer in southern China: Effects of dust storms and aerosol‐cloud interactions

AbstractAerosols and cloud water were analyzed at a mountaintop in the planetary boundary layer in southern China during March–May 2009, when two Asian dust storms occurred, to investigate the effects of aerosol‐cloud interactions (ACIs) on chemical evolution of atmospheric trace elements. Fe, Al, and Zn predominated in both coarse and fine aerosols, followed by high concentrations of toxic Pb, As, and Cd. Most of these aerosol trace elements, which were affected by dust storms, exhibited various increases in concentrations but consistent decreases in solubility. Zn, Fe, Al, and Pb were the most abundant trace elements in cloud water. The trace element concentrations exhibited logarithmic inverse relationships with the cloud liquid water content and were found highly pH dependent with minimum concentrations at the threshold of pH ~5.0. The calculation of Visual MINTEQ model showed that 80.7–96.3% of Fe(II), Zn(II), Pb(II), and Cu(II) existed in divalent free ions, while 71.7% of Fe(III) and 71.5% of Al(III) were complexed by oxalate and fluoride, respectively. ACIs could markedly change the speciation distributions of trace elements in cloud water by pH modification. The in‐cloud scavenging of aerosol trace elements likely reached a peak after the first 2–3 h of cloud processing, with scavenging ratios between 0.12 for Cr and 0.57 for Pb. The increases of the trace element solubility (4–33%) were determined in both in‐cloud aerosols and postcloud aerosols. These results indicated the significant importance of aerosol‐cloud interactions to the evolution of trace elements during the first several cloud condensation/evaporation cycles.

Phytostabilisation of severely contaminated mine tailings using halophytes and field addition of organic and inorganic amendments

Phytostabilisation strategies have proven to be an efficient remediation option for mine tailings, but the adequate plant species and amendments have to be carefully selected. A remediation experiment was carried out at the semi-field level in tailings (pH 3.2, ≈1100, 4700 and 5000 mg kg−1 of As, Pb and Zn, respectively) from the mining district of La Unión-Cartagena (SE Spain). A red mud derivative (Fe/Al oxides), its combination with compost, and hydrated lime (Ca hydroxide) were applied in field plots of 0.25 m2. After four months of field stabilisation, tailings were transferred unaltered to a plant growth facility, and Atriplex halimus and Zygophyllum fabago (halophytes) were sown. Three months later, trace element (TE) solubility, plant accumulation and chemical speciation in the tailings pore water were studied. In unamended tailings, soluble TEs concentrations were very high (e.g., 40 mg Zn l−1), the dominant species being free ions and SO42-- complexes (>70%). The addition of amendments increased tailings pH (6.7–7), reduced TEs solubility and extractability (>80–99%) and changed the dominant species of soluble Al, Cu, Pb and Zn to hydroxides and/or organo-metallic complexes, but increased slightly the extractable As and soluble Tl concentrations. Plants were able to grow only in amended tailings, and both species presented low levels of Al, As, Cd and Zn. Therefore, the use of combined red mud derivative and compost and halophytes was shown to be a good phytostabilisation strategy, although the dose applied must be carefully chosen in order to avoid possible solubilisation of As and Tl.

Solubility of aerosol trace elements: Sources and deposition fluxes in the Canary Region

African dust inputs have important effects on the climate and marine biogeochemistry of the subtropical North Atlantic Ocean. The impact of dust inputs on oceanic carbon uptake and climate is dependent on total dust deposition fluxes as well as the bioavailability of nutrients and metals in the dust. In this work, the solubility of trace metals (Fe, Al, Mn, Co and Cu) and ions (Ca, sulphate, nitrate and phosphate) has been estimated from the analysis of a long-time series of 109 samples collected over a 3-year period in the Canary Islands. Solubility is primarily a function of aerosol origin, with higher solubility values corresponding to aerosols with more anthropogenic influence. Using soluble fractions of trace elements measured in this work, atmospheric deposition fluxes of soluble metals and nutrients have been calculated. Inputs of dissolved nutrients (P, N and Fe) have been estimated for the mixed layer. Considering that P is the limiting factor when ratios of these elements are compared with phytoplankton requirements, an increase of 0.58 nM of P in the mixed layer (∼150 m depth) and in a year can be estimated, which can support an increase of 0.02 μg Chla L−1 y−1. These atmospheric inputs of trace metals and nutrients appear to be significant relative to the concentrations reported in this region, especially during the summer months when the water column is more stratified and deep-water nutrient inputs are reduced.

Shrubs for the remediation of contaminated Mediterranean areas: Is the nurse effect mediated by increases in soil enzyme activities?

The use of shrubs as nurse plants to facilitate woody plant recruitment has been proved to be particularly useful for the revegetation of highly disturbed environments, such as contaminated lands. In a contaminated area from SW Spain, we compared soil fertility and microbial enzyme activity in different microhabitats associated with shrubs, along a gradient of soil contamination, 13 years after the revegetation of the area following a contamination episode. We compared soil organic matter, nutrient content, and enzyme activities in four microhabitats: underneath retama (Retama sphaerocarpa) shrubs nursing Holm oak (Quercus ilex subsp. ballota) seedlings, underneath separate retama and oak individual plants, and in patches of soil without any woody cover. Soil enzyme activities were influenced more by the background soil conditions (pH and organic matter content, modified by the addition of a soil amendment during soil remediation) than by the development of the vegetation. In the soils under the cover of the retama-oak association, intense acidification (pH <4) was observed at the most contaminated sites, which resulted in higher solubility of toxic trace elements and lower enzyme activities (five times lower dehydrogenase and β-glucosidase activities, in comparison to neutral soils). The results suggest that improving soil conditions before plantation through amendment application is critical to ensure the improvement of microbial activity in the long-term at such degraded sites.

Near-road enhancement and solubility of fine and coarse particulate matter trace elements near a major interstate in Detroit, Michigan

Communities near major roadways are disproportionately affected by traffic-related air pollution which can contribute to adverse health outcomes. The specific role of particulate matter (PM) from traffic sources is not fully understood due to complex emissions processes and physical/chemical properties of PM in the near-road environment. To investigate the spatial profile and water solubility of elemental PM species near a major roadway, filter-based measurements of fine (PM2.5) and coarse (PM10-2.5) PM were simultaneously collected at multiple distances (10 m, 100 m, and 300 m) from Interstate I-96 in Detroit, Michigan during September–November 2010. Filters were extracted in water, followed by a hot acid extraction, and analyzed by magnetic sector field high resolution inductively coupled plasma mass spectrometry (HR-ICPMS) to quantify water-soluble and acid-soluble trace elements for each PM size fraction. PM2.5 and PM10-2.5 species measured in the near-road samples included elements associated with traffic activity, local industrial sources, and regional pollution. Metals indicative of brake wear (Ba, Cu) were dramatically enriched near the roadway during downwind conditions (factor of 5 concentration increase), with the largest increase within 100 m of the roadway. Moderate near-roadway increases were observed for crustal elements and other traffic-related PM (Fe, Ca), and the lowest increases observed for regional PM species (S). Water solubility varied by PM species and size, and for PM2.5 included highly (S, K, Ca, Mg, Zn, Ba), moderately (Cu, Mn, Sb, Pb), and minimally (Fe, Ti) water-soluble species, with lower water solubility for most species in PM10-2.5. Results from this study indicate that water-soluble PM2.5 and PM10-2.5 metals, particularly from brake/tire wear, were enhanced in the near-roadway environment which may have human health implications.

Design strategy for controlled natural aging in Al–Mg–Si alloys

This study presents a design strategy for Al–Mg–Si alloys to control natural aging. Recently, trace addition of Sn was shown to suppress natural aging for up to two weeks, which was explained by the strong trapping of vacancies to Sn atoms. Here we explore the effect of solution treatment temperature, the combination of trace elements such as Sn and In, and the composition of main hardening elements Mg, Si and Cu on natural aging. The results are discussed based on the dissolvable amount of trace elements and their effect on diffusion retardation, and solute clustering mechanisms in Al–Mg–Si alloys. Thermodynamic calculations using the CALPHAD approach show that maximum retardation of natural aging is achievable at the highest trace element solubility, which exists at significantly different solution treatment temperatures for Sn or In. The effects of Mg, Si and Cu content on natural aging kinetics are interpreted via their influence on the Sn solubility and clustering mechanisms. It is proposed that Sn additions reduce the concentration of excess vacancies, which is most important for early Si clustering, and that the effect of Cu is comparable to the effect of Sn, but less pronounced. Based on the investigated parameter space, a design concept is proposed and an Al–Mg–Si alloy showing suppression of natural aging for >6 months and significant artificial aging potential is demonstrated.

Alleviation of environmental risks associated with severely contaminated mine tailings using amendments: Modeling of trace element speciation, solubility, and plant accumulation.

Tailings are considered one of the most relevant sources of contamination associated with mining activities. Phytostabilization of mine spoils may need the application of the adequate combination of amendments to facilitate plant establishment and reduce their environmental impact. Two pot experiments were set up to assess the capability of 2 inorganic materials (calcium carbonate and a red mud derivate, ViroBindTM ), alone or in combination with organic amendments, for the stabilization of highly acidic trace element-contaminated mine tailings using Atriplex halimus. The effects of the treatments on tailings and porewater physico-chemical properties and trace-element accumulation by the plants, as well as the processes governing trace elements speciation and solubility in soil solution and their bioavailability were modeled. The application of the amendments increased tailings pH and decreased (>99%) trace elements solubility in porewater, but also changed the speciation of soluble Cd, Cu, and Pb. All the treatments made A. halimus growth in the tailings possible; organic amendments increased plant biomass and nutritional status, and reduced trace-element accumulation in the plants. Tailings amendments modified trace-element speciation in porewater (favoring the formation of chlorides and/or organo-metallic forms) and their solubility and plant uptake, which were found to be mainly governed by tailing/porewater pH, electrical conductivity, and organic carbon content, as well as soluble/available trace-element concentrations. Environ Toxicol Chem 2016;35:2874-2884. © 2016 SETAC.

Compositional effects on the solubility of minor and trace elements in oxide spinel minerals: Insights from crystal-crystal partition coefficients in chromite exsolution

F.P.I. grant of the Ministerio de Econonia y Competitividad (Spain) BES-2011-045423 FONDECYT 11140005 Millenium Nucleus for Metal Tracing Along Subduction NC130065 DEST Systemic Infrastructure Grants ARC LIEF NCRIS Macquarie University CGL2010-15171

Functional effects of manganese and iron oxides on the dynamics of trace elements in soils with a special focus on arsenic and cadmium: A review

The dynamics and availability of arsenic (As), cadmium (Cd), and other trace elements in soils are of great concern to soil scientists. Owing to the human toxicity of As and Cd, the Codex Alimentarius Commission set maximum permissible concentrations of these elements in foodstuffs, including rice which is a major source of human intake of As and Cd, especially in Asia. Therefore, attenuation of As and Cd concentrations in crops, especially rice, is important for both human health and agroindustry.Manganese (Mn) and iron (Fe) oxides have great capacity to sorb trace elements. Adsorption of cationic elements increases with increasing pH, whereas adsorption of arsenate [As(V)] shows the opposite trend. Adsorption of cationic elements by Mn oxides is generally much greater than adsorption by Fe oxides, whereas Fe oxides have a much higher adsorption capacity for As than Mn oxides do. Trace elements can co-precipitate with Mn/Fe oxides and are subsequently released from or incorporated into solid phases with aging depending on the natures of elements and on the surrounding conditions. Moreover, Mn/Fe oxides, especially Mn oxides, oxidize arsenite [As(III)] to As(V), which is less soluble. Sorbed elements solubilize under reducing conditions through reductive dissolution of Mn/Fe oxides. In addition to the transformation of As from As(V) to As(III), the release of As from Fe oxides is responsible for the increase in dissolved As concentration that accompanies flooding. In contrast, Cd precipitates as barely soluble sulfides under strong reducing conditions. This difference may explain why the concentrations of As and Cd in rice grown with different water management show opposite trends. Iron plaque, an Fe oxide precipitate that forms on rice roots, may attenuate As concentrations in rice tissues by fixing and sequestering As, although some studies have questioned this possibility.There have been many attempts to use Mn/Fe oxides (or materials containing them) to attenuate the soil solubility of trace elements and/or reduce their uptake by crops. Application of Mn/Fe oxides has useful effects in most cases; in particular, application of Fe oxides or Fe oxide-containing materials immobilizes As in soils. Therefore, application of Mn/Fe oxides combined with flooded cultivation may attenuate the concentrations of both As and Cd in rice. However, additional studies are required because only a few studies have focused on the effects of application of Mn/Fe oxides on As mobility in anaerobic soils and consequent uptake by rice plants.

Trace Metal Availability and Soil Quality Index Relationships under Different Land Uses

Long-term intensive agriculture without appropriate management is likely to cause soil degradation. Therefore, monitoring of soil quality in agricultural regions is essential for protecting soil and water resources and providing high-quality and safe food. Our objective was to quantify potential soil degradation by assessing trace element solubility and other major soil properties. We used principal component analysis to select, weight, and score soil quality indicators before combining them into a soil quality index (SQI). Nineteen soil properties were quantified, but only 10 showed significant differences between forest and agricultural land uses. Four soil properties (pH, soil organic C, bulk density, and ammonium lactate extractable P) were chosen as indicators of soil quality. We found no statistical differences in overall SQI values between the two land uses, but differences in single soil properties such as soil organic C and bulk density did indicate some degradation due to agricultural practices. Trace metal availability and solubility showed no significant correlation with overall SQI values, indicating that our method for determining SQI was not a good indicator of trace metal availability and solubility.