Fe-Mn Oxides Research Articles

The symbiotic system of sulfate-reducing bacteria and clay-sized fraction of purplish soil strengthens cadmium fixation through iron-bearing minerals

The microbe-clay mineral system is widely known to reduce the fluidity of heavy metals through biomineralization, thus mitigating soil pollution stemming from heavy metals. Here, we investigated the effect of mineral distinction on the solidification of cadmium (Cd) using sulfate-reducing bacteria (SRB) to construct symbiotic systems with purplish soil, clay-sized fraction of purple soil (Clay-csp), clay particles of amorphous iron (Fe) oxide (Clay-ox), clay particles removing crystalline Fe oxide (Clay-CBD), and residues of Clay-CBD treated by hydrochloric acid (Clay-HCl). The difference in Cd morphology among purplish soil, Clay-csp, and Clay-ox indicated that the fixation of Cd in soil was largely determined by Fe oxides. The content of Cd in Clay-csp decreased by 66.7% after the removal of amorphous Fe, confirming that clay easily adsorbed infinitive Fe oxides in purple soil. In the system of SRB and Clay-ox, carbonate-bound Cd (F2) decreased by 14.85% and residual Cd (F5) increased by 14% from the retardation to late decline phase, eventually forming iron-sulfur (Fe-S) compounds. Based on the correlation analyses of Cd and Fe in amorphous-bound state and Fe-manganese (Mn) oxidation state in simulation experiments, it is demonstrated that Fe-Mn oxides control the behavior of Cd in soil clay, and SRB-mediated Fe-bearing minerals promote the transformation of Cd from activated to stable state.

Source to sink analysis of weathering fluxes in Lake Baikal and its watershed based on riverine fluxes, elemental lake budgets, REE patterns, and radiogenic (Nd, Sr) and 10Be/9Be isotopes

We present a detailed analysis of weathering fluxes at Lake Baikal, the largest lake in the world, using the major element, trace element and isotope geochemistry of major inflowing rivers, the lake itself, and its sediments. Our objective is to assess how lake records could be used to understand river-catchment-scale denudation and weathering processes.Total denudation rates at Lake Baikal, as obtained from meteoric 10Be/9Be, are an order of magnitude lower than the global average, at 16–35 t km−2 yr−1. Chemical weathering rates obtained from the riverine dissolved load and discharge are, on the other hand, in the same range as global values, at 6–29 t km−2 yr−1. Chemical weathering rates are higher in the north of the catchment than in the south, consistent with higher runoff in the north. In contrast, 10Be/9Be-derived denudation rates are higher in the south. We hypothesize that this pattern of variation may be due to the stabilizing effect of permafrost soils preventing erosion in the north. An inverse model shows that the Selenga River, Lake Baikal’s major tributary, has a silicate weathering contribution to riverine dissolved cation fluxes of 42 mol%; this and other characteristics are representative of large rivers globally. Many trace elements have much lower concentrations in the lake than in inflowing rivers (Be (5%), Mn (3%), Fe (0.4%) and REE (1–2%)). We suggest, based on REE patterns and Mn, Fe-depth profiles in the lake, that this removal is the result of pH induced changes in dissolved-adsorbed partitioning at the river-lake interface, and the incorporation of trace elements into authigenic Fe-Mn (oxyhydr)oxide phases forming within the lake. Strontium is isotopically uniform within the lake, demonstrating that the whole lake mixes on a timescale shorter than its residence time (<330 years). Neodymium and Be, in contrast, show isotopic variability between the basins. While the Sr isotope budget of the lake is largely consistent with observed riverine Sr fluxes, an unradiogenic Nd source is needed to explain lake Nd isotope compositions, especially in the Northern Basin. This source appears to derive from old crustal rocks in this part of the catchment and could be hydrothermal, or small rivers that were not sampled here. Similarly, elevated 10Be/9Be ratios in the lake basins relative to the river input imply variable but significant atmospheric inputs of 10Be into the lake.Overall, this study demonstrates that records of the paleo-chemistry of lakes, and Lake Baikal in particular, hold promise for understanding denudation and weathering on the continents, in ways that are more directly relatable to the environmental conditions of the catchment than is possible with marine records.

Flooding-drainage regulate the availability and mobility process of Fe, Mn, Cd, and As at paddy soil

Speciation changes in Fe and Mn during the soil flooding-drainage process strongly affect the Cd and As bioavailability in paddy soils. However, owing to a lack of in-situ dynamic monitoring technology, the regularity and mechanism of synergetic changes in Fe, Mn, Cd, and As in paddy soils have not been sufficiently studied. Diffusive gradients in thin films (DGT) were used to investigate the dissolution/transformation process of FeMn oxides and their effects on the bioavailability of Cd and As in three contaminated paddy fields that underwent incubated flooding for 40 d followed by a 20 d oxidation period. In-situ monitoring showed that the labile Cd concentrations decreased rapidly upon flooding but bioavailability of As increased significantly, with As and Cd concentrations largely depending upon Fe (II) content. We discovered that the transformation pathway of Iron Oxide-LDH (FeII-FeIII)-Goethite was the key process in reducing the activity of soil Cd. A higher Mn/Fe ratio and lower organic matter content delayed the Fe reduction process, which subsequently delayed Cd immobilization. Mobilization of Cd upon soil drainage was caused by a decrease in soil pH resulting in the release of Cd from secondary minerals.

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

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

A review of retrieving pristine rare earth element signatures from carbonates

Rare earth element and yttrium (REY) concentrations of carbonates can be used as potential proxies to trace the geochemistry of precipitating waters and physico-chemical environments. However, it is difficult to retrieve pristine REY signatures of carbonates because they can be contaminated by non-carbonate phases and modified by post-depositional processes. In this paper, we review the controlling factors of the REY signatures, such as the total REE concentrations, REY patterns, as well as elemental anomalies (mainly La, Ce, Eu and Gd), and Y/Ho ratios from published information. The non-carbonate phases, including clastic detritus, Fe-Mn(oxyhydr)oxides and phosphates, and post-depositional modification are the important factors that contaminate pristine REY signatures. The useful proxies and relationships among element concentrations, anomalies, and ratios can be used to evaluate the non-carbonate contamination or post-depositional modification. The selection of suitable normalization standards is also critical in certain cases. We evaluate the appropriate analytical methods, dissolution processes and pre-leaches to minimize the influence of non-carbonate contamination and post-depositional modification. We conclude that partial dissolution with acetic acid may be a robust approach to retrieve pristine REY signatures from the bulk carbonates, whereas LA-ICP-MS technique is appropriate for in-situ analyses of pure carbonate microfacies. • Influencing factors of REY signatures of carbonates are reviewed. • Pristine REY signatures can be contaminated by non-carbonate phases and post-depositional modification. • Appropriate normalization standards should be selected in certain cases. • Approaches to retrieve pristine REY signatures are proposed.

The Effect of Compost and Apatite on Pb Distribution in the Pb- Contaminated Soil

There are various techniques for rehabilitating soils contaminated by heavy metals, such as physical treatment, chemical treatment, and phytoremediation. Pb-contaminated soils are mostly treated with soil mixing, soil dressing, or soil washing. In this study, hydroxyapatite powder and organic compost of different mix ratios were added to two kinds of high-concentration synthesized Pb-contaminated soils (1000 mg/kg), which were processed with sequential extraction schemes after different incubation periods in order to examine the distribution of Pb forms in them. The form distributions analyzed included the exchangeable form Pb (PbE), Fe-Mn oxidation form Pb (PbFe-Mn), organic bonded form Pb (PbO), and residual form Pb (PbR). The findings indicated that after stabilization for one month, the alkaline Tk series soil was less susceptible to Pb contamination when no hydroxyapatite and compost was applied, which made it more difficult for Pb in the soil to interact with cations and trigger exchange reactions. Next, the PbR concentrations of the two soils tested were higher after hydroxyapatite was added. This result suggested that hydroxyapatite helped to stabilize the Pb in the soil samples and prevented it from precipitating, thereby controlling the Pb concentration at a certain level to avoid contamination. Lastly, when hydroxyapatite and compost of different mix ratios were applied to the two kinds of Pb-contaminated soils, we found that the PbE concentration of the Tk series soil declined as the concentration of compost increased, suggesting that increasing the compost concentration raised the pH value of the soil and enhanced its fertility. On the other hand, the PbE concentration of the Lp series soil increased as the compost concentration rose, indicating that an increase in compost concentration hampered plants from absorbing soluble nutrients in the soil, thereby making it easier for Pb to precipitate via cation exchange and resulting in Pb contamination.

Combined experimental and theoretical study of o-xylene elimination on Fe–Mn oxides catalysts

The development of low-cost and easily accessible catalysts to realize the practical applications of catalytic combustion of volatile organic compounds remains a challenge. In this work, a series of Fe–Mn oxides catalysts were prepared via a facile redox-precipitation route for the elimination of o-xylene. Among the synthesized catalysts, Fe3Mn1-RP exhibited excellent activity for o-xylene elimination with a T50 and T90 of 223 °C and 236 °C, respectively (o-xylene concentration = 500 ppm, WHSV = 36,000 mL g−1 h−1). Characterization results demonstrated that superior catalytic activity could be achieved from large specific surface area, good reducibility and high proportion of Mn4+. Besides, high Fe contents proved beneficial in generating additional oxygen vacancies, thereby improving the performance of the catalyst. The stable crystal structures and surface electron density distributions of the catalysts, and adsorption sites of o-xylene on the catalyst surface, were also determined through density functional theory (DFT) calculations to provide an in-depth mechanism on how the o-xylene oxidation occurred. Moreover, analysis of the energy barrier during the oxidation process proved that the ring-opening reaction on the surface of Fe3Mn1-RP with an activation energy as low as 2.46 eV would more likely occur via oxygen vacancies.

Reactivity Study of Bimetallic Fe-Mn Oxides with Addition of TiO2 for Chemical Looping Combustion Purposes

The objective of the research was to prepare Mn-based materials for use as oxygen carriers and investigate their reactivity in terms of their applicability to energy systems. The family of Fe2O3-MnO2 with the addition of TiO2 was prepared by mechanical mixing method and calcination. Five samples with addition of Fe2O3 (20, 30, 35, and 50 wt.%) to MnO2 (65, 55, 50, 35, and 85 wt.%) with constant amount of inert TiO2 (15 wt.%) were prepared. The performance of TiO2 supported Fe-Mn oxides oxygen carriers with hydrogen/air in an innovative combustion technology known as chemical looping combustion (CLC) was evaluated. Thermogravimetric analysis was used for reactivity studies within a wide temperature range (800–1000 °C). Comprehensive characterization contained multipurpose techniques for newly synthesized materials. Moreover, post-reaction experiments considered morphology analysis by SEM, mechanical strength testing by dynamometry, and crystal phase study by XRD. Based on wide-ranging testing, the F50M35 sample was indicated as the most promising for gaseous fuel combustion via CLC at 850–900 °C temperature.

Buried Fe-Mn nodules on the World ocean floor

Ocean floor Fe-Mn nodule sequence is a product of Mesozoic-Cenozoic global epoch of Fe-Mn oxide ore accumulation. Buried nodules formed in Late Paleocene-Eocene, Late Cretaceous, Cenomanian.

Mechanochemically synthesized Fe-Mn binary oxides for efficient As(III) removal: Insight into the origin of synergy action from mutual Fe and Mn doping

Iron manganese oxide resources are widely derived from the geological structure, and their combinations play an important role in the migration and transformation of arsenic. Iron oxide and manganese oxide exist generally in a mixed state in Fe-Mn oxides synthesized via the well studied co-precipitation methods using potassium permanganate and manganese/iron sulfates. Herein, a newly designed Fe-Mn-O compositing oxide with Fe-MnO2, Mn-Fe2O3, (Fe0.67Mn0.33)OOH solid solution and FeOOH as the main components, simply through solvent-free mechanical ball milling pyrolusite (MnO2) and ferrihydrite (FeOOH) together has been reported. Atomic-scale integrations by doping Fe and Mn with each other were detected and an adsorption-oxidation bifunctionality was achieved, where Fe-doped MnO2 served as oxidizer for As(III) and amorphous/ground FeOOH acted as adsorbent first for As(III) and then As(V) from the oxidization. The maximal adsorption for As(III) could reach 44.99 mg/g and over 82.5% of As(III) was converted to As(V). More importantly, high removal ability of arsenic worked in a wide pH range of 2–10.5%, and 87.2% of its initial adsorption-oxidation capacity could be kept even after 5-cycles reuse for treating 20 mg/L As(III) with a dosage at 1 g/L. Together with the enhanced adsorption capacity by the milled FeOOH, surface electron transfer efficiency of the developed Fe-MnO2 surrounded with Mn-Fe2O3 has been studied for the first time to understand the oxidization effect to As(V). Besides the environment-friendliness of ball milling method, the prepared sample is quite stable without noticeable metal release into solution. Mechanism studies of arsenic removal by the as-prepared Fe-Mn-O oxide provide a new direction for improving the oxidation efficiency of MnO2 to As(III) based on the widely available cheap Mn and Fe oxides, contributing to the development of advanced oxidization process in the treatment of waste water.

Cd diminution through microbial mediated degraded lignocellulose maize straw: Batch adsorption and bioavailability trails

Lignocellulose degraded maize straw (LMS) was prepared with the interaction of soil-indigenous microorganisms and further deployed to attenuate the Cd contamination in polluted soil. The Lignocellulose degrading ratio was determined and results revealed the significant degradation of cellulose, hemicellulose and lignin by 33.03, 26.7 and 15.97% respectively as compared to pristine maize straw (PS). Moreover, LMS was also categorized through FE-SEM, FTIR, BET analysis, elemental analysis and XPS technique and the analytical results indicated that lignocellulose structure in maize straw was successfully degraded and was involved in metal-ion complexation. Batch sorption trials revealed that Cd2+ sorption onto LMS was explained well by Langmuir isotherm and pseudo-second-order kinetic model. The LMS showed maximum adsorption capacities (9.84 mg g−1) for Cd2+ as compared to PS (3.30 mg g−1). Moreover, the soil incubation trials (60 days) depicted the availability of Cd decreased by 11.03 and 34.7% with PS and LMS application respectively. The addition of LMS significantly decreased the exchangeable fractions of Cd and ensued an increase in organic matter and Fe–Mn oxides bound fractions. This work clarified the LMS as a promising amendment for effective remediation of Cd-contaminated matrices.

Extremely Stable and Durable Mixed Fe–Mn Oxides Supported on ZrO2 for Practical Utilization in CLOU and CLC Processes

This paper contains the results of research on a promising combustion technology known as chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU). The remarkable advantages of CLC are, among others, that concentrated CO2 stream can be obtained after water condensation without any energy penalty for its separation or significant decrease of NOx emissions. The objective of this work was to prepare a novel bi-metallic Fe–Mn supported on ZrO2 oxygen carriers. Performance of these carriers for the CLOU and CLC process with nitrogen/air and hard coal/air was evaluated. One-cycle CLC tests were conducted with supported Fe–Mn oxygen carriers in thermogravimetric analyzer utilizing hard coal as a fuel. The effects of the oxygen carrier chemical composition and process temperature on the reaction rates were determined. Our study proved that for CLOU, properties formation of bixbyite and spinel forms are responsible. Among iron ferrites, we concluded that iron-rich compounds such as Fe2MnO4 over FeMn2O4 spinel type oxides are more effective for CLOU applications.

Combined Use of Calciprill and Sodium Silicate Improves Chemical Properties of Low-pH Soil

The highly weathered, acidic tropical soils are generally less fertile because of their low pH, high exchangeable acidity, and Al, Fe, and Mn saturations. Using soil amendments to solve the aforementioned problems is essential. To this end, Calciprill and sodium silicate are worth considering because of their high neutralizing value and dissolution to suppress exchangeable acidity and Al, Fe, and Mn hydrolysis, while at the same time increasing soil pH to improve the availability of inorganic N, available P, exchangeable base cations, and Effective Cation Exchange Capacity (ECEC). An incubation study was conducted to determine the right combination of Calciprill and sodium silicate to reduce exchangeable acidity and Al and Fe hydrolysis to improve inorganic N, available P, exchangeable base cations availability, and ECEC. Bekenu series (Typic Paleudults) was incubated with a combined use of Calciprill at 80%, 90%, and 100% Ca saturations and sodium silicate at 90, 105, 120, 135, and 150 kg ha−1 for 40, 80, and 120 days, respectively. The laboratory incubation study was carried out using a Completely Randomized Design (CRD) with triplicates to determine the aforementioned treatment effects of the combined use of Calciprill and sodium silicate on soil pH, exchangeable, Al, inorganic N, available P, electrical conductivity, exchangeable cations (K, Ca, Mg, Na, Fe, and Mn), and ECEC using standard procedures. Soils with both amendments significantly increased soil inorganic N, available P, electrical conductivity, exchangeable base cations (K, Ca, Mg, and Na), and ECEC. This was because the amendments increased soil pH by suppressing exchangeable acidity. Moreover, they transformed Al, Fe, and Mn ions into insoluble compounds such as Al and Fe hydroxides and Mn oxides because of their high inherent exchangeable cations, especially Ca and Na. This suggests that the combined use of Calciprill and sodium silicate can enhance soil productivity. The most suitable combination is 7.80 g Calciprill and 9.26 g sodium silicate (C3S5) per one kilogram soil. Additionally, the findings provide fundamental information for future greenhouse and field trials to determine the effects of the suitable combination of the amendments uncovered by this present study on soil health and crop productivity.

Soil aggregate stability and its response to overland flow in successive Eucalyptus plantations in subtropical China

Soil aggregates constitute the basic units of the soil structure, and soil aggregate stability is an important indicator of soil erodibility. Successive planting of fast-growing plantations can change the erosion resistance of the soil under rainfall conditions. Pure Eucalyptus plantations in this study (first- to fourth-generations, i.e., I, II, III, and IV, respectively) were investigated. The stability and abrasion characteristics of soil aggregates were analyzed by the wet sieving method, the Le Bissonnais (LB) method and a slope flow scouring experiment. With an increase in successive generations of Eucalyptus, the soil bulk density increased, and the saturated water content, porosity, organic matter and Iron, Aluminum and Manganese (Fe-Al-Mn) oxide contents decreased. Additionally, the wet sieving results showed that the first- and second-generations had higher macroaggregate content than the fourth generation. The mean weight diameter (MWD) values decreased with the number of planting significantly. Based on fast wetting (FW), slow wetting (SW) and mechanical breakdown by shaking after pre-wetting (WS), the aggregate stability was ranked in a decreasing order as MWDSW > MWDWS > MWDFW. The relative dissipation index (RSI) and mechanical crushing index (RMI) increased with increasing number of planting generations. Aggregate stability was significantly negatively correlated with the soil bulk density and was significantly positively correlated with the organic matter and Fe-Mn oxide contents. The extent of aggregate abrasion (Wr/Wi) values and MWD values decreased with increasing scouring distance and slope gradient during the transport process. The α and Wr/Wi values of the scoured aggregates were significantly correlated with aggregate stability. Hence, with successive planting of Eucalyptus, the soil aggregate stability decreased, and the soil was prone to erosion when subjected to slope flow.

Comparative analysis of Cd fractional composition in soils under anthropogenic and artificial pollution

The composition of cadmium (Cd) compounds in soils of both technogenic landscapes and a model experiment were studied using the sequential fractionation method. A model experiment was conducted with artificial soil contamination by easily soluble Cd compounds. Pollution doses simulated the level of pollutant content in the studied soils of the impact zones and corresponded to low, high, and very high pollution. Fractions revealed both general features and specific metal distribution characteristics in anthropogenically polluted soil and soil under artificial pollution. The largest amount of Cd in the soils was concentrated in the residual fraction (up to 60%). With increasing pollution level, the proportion of the residual fraction decreases and the proportion of mobile compounds (exchangeable fraction and carbonate fraction) of the metal increases (up to 22% and 18%, respectively). In contaminated soil, carbonates and Fe-Mn oxides play the main role in the Cd fractional distribution. Fractional distribution of Cd shows general regularities both under anthropogenic pollution and under artificial contamination; however, metal demonstrated high mobility at artificially contamination.

Effects of sulfur dosage on continuous bioleaching of heavy metals from contaminated sediment

The bioleaching technology has been considered as a promising green technology for remediation of contaminated sediments in recent years. Bioleaching technology was generally conducted in the batch bioreactor; however, the continuous bioreactor should be developed for the application of bioleaching technology in the future. The purposes of this study were to establish a continuous bioleaching process, and to evaluate the effects of sulfur dosage on the efficiency of metal removal during this continuous bioleaching process. The obtained results show that the pH decrease, sulfate production and metal removal efficiency all increased with increasing sulfur dosage in the continuous bioleaching process due to high substrate concentration for sulfur-oxidizing bacteria. After 30 days of operation time, the maximum solubilization efficiencies for Zn, Ni, Cu and Cr were found to be 78%, 90%, 88% and 68%, respectively, at 5% of sulfur dosage. After the bioleaching process, heavy metals bound in the carbonates, Fe-Mn oxides and organics/sulfides in the sediment were effectively removed and the potential ecological and toxic risks of treated sediment were greatly reduced. The results of bacterial community analyses demonstrated that this continuous bioleaching process were dominated by several acidophilic sulfur-oxidizing bacteria; S. thermosulfidooxidans, At. thiooxidans/At. ferrooxidans, S. thermotolerans and At. albertensis, whereas the percentage of less-acidophilic sulfur-oxidizing bacteria (T. thioparus and T. cuprina) was lower than 15% of total bacteria. In addition, the cell numbers of sulfur-oxidizing bacteria increased as the sulfur dosage was increased in the continuous bioleaching process.

EFFECT OF SOIL IRRIGATION WITH WASTEWATER ON NI FRACTIONS IN SOME CONTAMINATED SOILS IN EGYPT

In this study Ni species were determined using a sequential extraction technique. The method consists of sequential extraction of the soil with different solutions, and it is designed to separate into six operationally defined fractions namely water soluble, exchangeable, carbonate bound, Fe-Mn oxides bound, organic bound and residual fractions. The objectives of this study were to investigate nickel forms in tested soils and to determine the effect of industrial wastewater effluent irrigation on the metal fractions in soil. Data showed a remarkable increase in all tested Ni-forms in polluted soil. It could be concluded that soil composition has been changed with depth. Especially under such condition whereas, metal soluble organic compounds found in wastewater may precipitate and percolates through soil and may transport soluble Ni with the soil solution.

The IRIS Imager: A freeware program for quantification of paint removal on IRIS films

AbstractSoils with seasonal or continuous water saturation are characterized by unique redox‐related processes including Fe and Mn oxide reduction. Indicators of reduction in soils (IRIS) devices were created as low‐cost, direct sensors of such reduced chemistry. Such IRIS devices are painted with oxides of Fe or Mn, inserted into the soil, and then removed after a period of time; once removed, the paint lost due to reductive dissolution of these oxides is used to indicate the presence, location, and/or intensity of reducing conditions. However, quantifying the paint removal using existing methods can be subjective and time consuming. Here, we describe the use of the IRIS Imager, an image analysis program that calculates removal of paint from IRIS films in L*a*b* color space (where L* is lightness, a* is red–green value, and b* is blue–yellow value) by comparing the change in lightness between initial and final IRIS film images. Paint removal from films deployed in flooded rice (Oryza sativa L.) paddy soils were quantified using the IRIS Imager, the grid method, and chemical extractions of IRIS films. All three methods were suitable for quantification of paint removal, but the IRIS Imager provided additional statistics to assess heterogeneity in paint removal on individual films and a less subjective approach to quantifying Mn oxide paint removal when Fe oxidation on Mn films was present. This free software can be used with IRIS devices to reproducibly measure paint removal from Fe oxide and Mn oxide IRIS and Fe oxide precipitation on Mn oxide IRIS.

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

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

Changes in potentially toxic element concentration and potential ecological risk in topsoil caused by sewage sludge application on forestland: A 3-year field trial

Sewage sludge (SS) application on forest plantation soils as a fertilizer/soil amendment is increasingly becoming a forestry management measure. However, the potential risk of SS-derived potentially toxic elements (PTEs) is still a cause for concern. This research was carried out to evaluate PTEs behavior in SS applied as an amendment for forestland application purposes. Speciation and transformation perspectives on residual effects during a 3-year field experiment were evaluated. Sewage sludge was applied to soils under Eucalyptus urophylla S.T. Blake, Schima superba Gardn. et Champ, and Pinus elliottii Engelm plantations at 30 Mg·ha−1 (dry weight). We investigated the total concentrations of Cu, Zn, Pb, Cd, and Ni, as well as their concentrations of five fractions: exchangeable (F1), bound to carbonates (F2), Fe–Mn oxides (F3), organic matter (F4), and residual (F5) along with the 0–10 cm of a surface A horizon (topsoil) one day, one, two, and three years after SS application, respectively. Sewage sludge caused significant increase in PTEs total concentrations and proportion of fraction F1 or F2. The mobility index and potential ecological risk confirmed that the risk was linked to the presence of these PTEs, especially for Cd. The total concentration and corresponding ecological risks of PTEs in most cases decreased, suggesting a potential loss of PTEs from the topsoil system. The percentage of all PTEs in fractions F1–F4 decreased and that in F5 increased with time. These results illustrate that the residual and mobility of PTEs in the topsoil during SS utilization was lower than expected and more attention should be paid to the risk of PTEs transferring to other environments.