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This study investigated the mechanical properties of a series of Fe-Cr-Mn (Mo)-N alloys. The chromium content ranged from 16 to 18 mass%. The test alloys were produced by adding nitrided ferroalloys during melting in an induction furnace. Test specimens of each alloy were prepared for mechanical testing and microstructural observation. Tensile strength (TS) and elongation (EL) were determined. By increasing or decreasing the content of the chromium, it can directly affected on the values of the mechanical properties and the final microstructure. A series of experiments showed that increasing the chromium content by 1.46 mass% in the Fe-16Cr-8Mn (Mo)-N alloy led to a decrease in the TS value by 12% and in the EL value by 16.1%, while increasing the chromium content by 0.72 mass% in the Fe-16Cr-11Mn (Mo)-N alloy caused a decrease in the TS value by 6.1% and in the EL value by 16%. The chromium content of 16 mass % in the studied alloys was found to provide sufficient strength and a relatively high elongation value. The alloys can also contain a higher mass fraction of chromium, but to obtain a complete austenitic structure it is necessary to increase the content of manganese and nitrogen. [ABSTRACT FROM AUTHOR]

Treatment of industrial chemical wastes being discharged into the environment is rarely done in Nigeria. These wastes are known to contain heavy metals which when released untreated, accumulate in the soil and pose serious environmental problems thereafter. In this study, operationally determined speciation analysis and potential mobility factor of Chromium and Nickel were carried out in the Tannery, Dye pit, Ceramic and Plastic industry soils of Sharada Industrial Estate. Levels of metals in the various fractions were determined using Atomic Absorption Spectrophotometer (Buck 211VGP AAS). The results indicated that the total -1 concentrations of the heavy metals in these industries were 126.46, 116.28, 116.89 and 117.91 mg.kg for Ni; -1 1498.54, 1446.33, 164.52, 117.93 mg.kg for Cr, respectively. The residual fraction for Cr at the sites ranged from -1 -1 61.60 mg.kg at Plastic Industrial site to 706.85 mg.kg at Tannery site, while that of Ni ranged from 59.80 -1 -1 mg.kg at Plastic Industrial site to 84.98 mg.kg at Tannery site. Results showed that most of the Cr and Ni fractions were bound to the residual fraction indicating that they were as a result of the lithogenic property of the soil. The mobility of Ni and Cr were calculated using Potential Mobility Factor (PMF), which for Ni across all industries gave 10.52%, 13.37%, 13.85%, 14.90%, while for Cr, the values were 0.72%, 11.08%, 8.36%, 11.55%. The PMF for Ni appeared to have a higher value compared to that of Cr, but the two values were statistically the same as they fell within the same medium stability and risk class (10 < PMF = 30). Risk assessments of these metals in the soils were found to pose no immediate health challenges. [ABSTRACT FROM AUTHOR]

Background: Microbe–virus interactions have broad implications on the composition, function, and evolution of microbiomes. Elucidating the effects of environmental stresses on these interactions is critical to identify the ecological function of viral communities and understand microbiome environmental adaptation. Heavy metal-contaminated soils represent a relevant ecosystem to study the interplay between microbes, viruses, and environmental stressors. Results: Metagenomic analysis revealed that Cr pollution adversely altered the abundance, diversity, and composition of viral and bacterial communities. Host–phage linkage based on CRISPR indicated that, in soils with high Cr contamination, the abundance of phages associated with heavy metal-tolerant hosts increased, as did the relative abundance of phages with broad host ranges (identified as host–phage linkages across genera), which would facilitate transfection and broader distribution of heavy metal resistance genes in the bacterial community. Examining variations along the pollutant gradient, enhanced mutualistic phage–bacterium interactions were observed in the face of greater environmental stresses. Specifically, the fractions of lysogens in bacterial communities (identified by integrase genes within bacterial genomes and prophage induction assay by mitomycin-C) were positively correlated with Cr contamination levels. Furthermore, viral genomic analysis demonstrated that lysogenic phages under higher Cr-induced stresses carried more auxiliary metabolic genes regulating microbial heavy metal detoxification. Conclusion: With the intensification of Cr-induced environmental stresses, the composition, replication strategy, and ecological function of the phage community all evolve alongside the bacterial community to adapt to extreme habitats. These result in a transformation of the phage–bacterium interaction from parasitism to mutualism in extreme environments and underscore the influential role of phages in bacterial adaptation to pollution-related stress and in related biogeochemical processes. DMn-sMTAve77_Sk1oVrXtD Video Abstract [ABSTRACT FROM AUTHOR]

Shape memory alloys recover their original shape after deformation, making them useful for a variety of specialized applications. Superelastic behavior begins at the critical stress, which tends to increase with increasing temperature for metal shape memory alloys. Temperature dependence is a common feature that often restricts the use of metal shape memory alloys in applications. We discovered an iron-based superelastic alloy system in which the critical stress can be optimized. Our Fe-Mn-Al-Cr-Ni alloys have a controllable temperature dependence that goes from positive to negative, depending on the chromium content. This phenomenon includes a temperature-invariant stress dependence. This behavior is highly desirable for a range of outer space–based and other applications that involve large temperature fluctuations. [ABSTRACT FROM AUTHOR]

Abstract Mixed Cr(III)-Fe(III) (oxy)hydroxides are important Cr-bearing phases in natural, unpolluted soil. Fires frequently affect large areas of land around the world, causing the temporary development of elevated soil temperatures. This study examines the hypothesis that heating Cr(III)-Fe(III) (oxy)hydroxides at temperatures which occur in surface soils during fires can drive rapid oxidation of Cr(III) to hazardous Cr(VI). To test this, poorly-ordered Cr(III) x -Fe(III) 1- x (oxy)hydroxides, with x spanning 0.1 to 0.9, were heated at up to 800 °C for 2 h. Heating at 400–800 °C produced a highly crystalline hematite-eskolaite solid-solution (FeIII 2- n CrIII n O 3 , where n ranges from 0 to 2). Chromium K-edge X-ray absorption spectroscopy showed that during heating up to ∼40% of the initial Cr(III) was oxidized to Cr(VI), with the greatest extent of Cr(VI) formation occurring at 200–400 °C. At these temperatures, a substantial proportion (17%–70%) of the newly-formed Cr(VI) was exchangeable (i.e. extracted by a pH 7.2, 10 mM PO 4 3− solution). This suggests that much of the Cr(VI) formed by heating of Cr(III) x -Fe(III) 1- x (oxy)hydroxides at 200–400 °C is likely to be relatively mobile in fire-impacted soils. The results of this study provide new insights into a potentially-important pathway for the in-situ formation of Cr(VI) in soil. Graphical abstract Image 102 Highlights • Heating transforms Cr(III)-Fe(III)-(oxy)hydroxides to hematite/eskolaite. • During heating, up to 40% of solid-phase Cr(III) is rapidly oxidized to Cr(VI). • Cr(VI) formation depends on temperature and Cr(III)/Fe(III) substitution. • Much of the Cr(VI) formed at moderate temperature is readily mobile. [ABSTRACT FROM AUTHOR]

Abstract Tannery effluents are rich source of chromium (Cr) and organic carbon (C), however, hexavalent Cr (Cr6+) is many-fold more toxic than trivalent Cr (Cr3+). We examined the extent of total Cr, Cr3+ and Cr6+ pollution of agricultural soils under long-term tannery effluent irrigation in Kasur, Pakistan. Effects of Cr species on morphological and physiological responses of wheat including patterns of Cr3+ and Cr6+ uptake, their translocation factor (TF) and bioconcentration factor (BCF) were studied. Nine soil samples had significantly variable total organic C and total Cr, Cr3+ and Cr6+ contents. Pot study showed that morphological characteristics of wheat were largely unaffected by total Cr, Cr3+ and Cr6+ contents, however, physiological responses including contents of chlorophyll a, chlorophyll b, total chlorophyll, carotenoids and total proteins; and chlorophyll a:b ratio were significantly affected by contents of Cr species. Results further suggested that the relationships between total Cr and physiological attributes of wheat were controlled by Cr6+ rather than Cr3+ contents and, hence, Cr3+:Cr6+ ratios determined the effects of Cr on wheat growth and development. Uptake, TF and BCF values for Cr3+ and Cr6+ showed significant variations and BCF values showed negative correlation with total organic C contents. Results of our study highlight the significance of understanding the effects of Cr species and Cr3+:Cr6+ ratios rather than the total Cr contents when assessing the Cr behavior in soils and its effects on plant growth, especially phytotoxicity of tannery-based organic fertilizers before its application in the field. Graphical abstract Image 1 Highlights • Contrasting effects of Cr3+ and Cr6+ on wheat morphology and physiology. • Cr3+ and Cr6+ concentrations in plant tissues varies with Cr3+:Cr6+ ratio. • Bioconcentration factor (BCF) of Cr species correlated negatively with total organic C. • Soil organic C regulated the dynamics of Cr3+:Cr6+ ratio. • Cr3+:Cr6+ ratio was more important to assess the effects of Cr on wheat. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A Cr(VI)-reducing strain CRB-7 (Bacillus sp.) was isolated from Cr(VI) contaminated soil. • Complete reduction of 120 mg L−1 Cr(VI) was obtained within 48 h at pH 7.0 and 37 °C. • Various CRB-7 based immobilized biocomposites were synthesized for Cr(VI) reduction. • Humic acid (HA) as bacterial immobilized carrier for Cr(VI) reduction was first studied. • Suitable immobilized biobeads enhanced Cr(VI) removal, especially the HA-B-SA system. Abstract In this study, a novel Cr(VI) tolerant strain CRB-7 identified as Bacillus sp., was isolated and characterized for its high Cr(VI) reduction. The strain CRB-7 grew well and effectively reduced Cr(VI) under various conditions including pH (7–9), temperature (30–40 °C) and Cr(VI) concentrations (50–250 mg L−1). It almost completely reduced 120 mg L−1 Cr(VI) within 48 h under optimized condition of pH 7 and 37 °C. Further characterization by SEM-EDS and FTIR analyses indicated Cr(VI) removal mechanism of CRB-7 was predominately via bioreduction with little amount of bioadsorption. Furthermore, the strain CRB-7 based immobilized biobeads were successfully synthesized using five different porous materials as bacterial loading carrier respectively to ascertain the optimal immobilization biocomposite for Cr(VI) removal. CRB-7 cells immobilized with 3% sodium alginate (SA) and 5% humic acid (HA) exhibited the highest Cr(VI) removal efficiency. Moreover, immobilized biobeads have the advantages over free cells in being more stable and easier to reuse. High Cr(VI) reducing ability of the free and immobilized CRB-7 cells suggest the strain CRB-7, especially the B-HA-SA biocomposite is promising for remediating Cr(VI)-contaminated sites. [ABSTRACT FROM AUTHOR]

Abstract Iron oxides are important pedogenic Cr(III)-bearing phases which experience high-temperature alteration via fire-induced heating of surface soil. In this study, we examine if heating-induced alteration of Cr(III)-substituted Fe oxides can potentially facilitate rapid high-temperature oxidation of solid-phase Cr(III) to hazardous Cr(VI). Synthetic Cr(III)-substituted ferrihydrite, goethite and hematite were heated up to 800 °C for 2 h. Corresponding heating experiments were also conducted on an unpolluted Ferrosol-type soil, which had a total Cr content of 220 mg kg−1, initially undetectable Cr(VI) and Fe speciation comprising a mixture of hematite, goethite and ferrihydrite (according to Fe K-edge EXAFS spectroscopy). Up to ∼50% of the initial Cr(III) was oxidised to Cr(VI) during heating of Cr(III)-substituted ferrihydrite and hematite, with the greatest extent of Cr(VI) formation occurring at 200–400 °C. In contrast, heating of Cr(III)-substituted goethite resulted in up to ∼100% of Cr(III) oxidizing to Cr(VI) as the temperature approached 800 °C. In the Ferrosol-type soil, heating at ≥400 °C also resulted in large amounts of Cr(VI) formation, with a maximum total Cr(VI) concentration of 77 mg kg−1 forming at 600 °C (equating to oxidation of ∼35% of the soil's total Cr content). A relatively large portion (31–42%) of the total Cr(VI) which formed during heating of the soil was exchangeable, implying a high level of potential mobility and bioaccessibility. Overall, the results show that Cr(VI) forms rapidly via the oxidation of Fe oxide-bound Cr(III) at temperatures which occur in surface soils during fires. On this basis and given the frequency and extent of wild-fires around the world, we propose that fire-induced oxidation of Fe oxide-bound Cr(III) may represent a globally-significant pathway for the natural formation of hazardous Cr(VI) in surface soil. Graphical abstract Image 1 Highlights • Heating drives oxidation of Cr(III) substituted within Fe oxides to Cr(VI). • Fire-induced heating of unpolluted soil can drive hazardous Cr(VI) formation. • A large portion of newly-formed Cr(VI) is likely to be readily mobile. • Fire-induced Cr(III) oxidation may be an important pathway for Cr(VI) formation. Fire-induced oxidation of Fe oxide-bound Cr(III) may represent a largely unexplored, yet globally-significant pathway for the natural formation of hazardous Cr(VI) in soil. [ABSTRACT FROM AUTHOR]

Highlights • Cr mobility is related to the heavy fraction obtained from soil fractionation. • The mechanism of Cr mobility is suggested to be controlled by chromite weathering. • The heavy fraction corresponds to 0.6% of the bulk soil, containing 6.9% chromite. Abstract A laboratory study was conducted to assess the mobility and mechanisms of chromium release from soils obtained from an area of wide spread geogenic contamination. The agricultural soil sample used in this study was taken from the Schimatari area in Asopos River basin in Greece. In order to refine the isolation of minerals contained in the soil, two types of separation analysis were conducted. First, a size fractionation with hydrocyclone and second, a weight fractionation with heavy liquids. The separated fractions were characterized using chemical, mineralogical and surface analysis. The results provided consistent evidence that the heavy fraction of the soil is related directly to the mobile fraction of chromium. At acidic pHs, the clay-sized fraction also plays an additional important role in the mobility of Cr, due to the fact that this fraction has high surface area and chromium reactivity index. In addition, pH-edge leaching studies showed a high correlation between Cr–Ni, Cr–Mn and Cr–Y released from the soil which also suggests that the mobility of chromium is controlled by chromite weathering which is the case observed in Asopos river basin. [ABSTRACT FROM AUTHOR]

Abstract Lemon grass plants grown in Cr rich over burden soil of Sukinda chromite mine (India) countered Cr toxicity and oxidative stress with the production of reactive oxygen species and induced antioxidative defense system. Varied percentage of Cr rich over burden soil was applied to lemon grass pants to evaluate the actions of oxidative inhibitors enzymes extracted and assayed from both roots and shoots. The study also assessed the oil content and its composition in response to the different percentage of Cr available in over burden soil. In order to evaluate the defense system of a plant against oxidative stress and determine the level of reactive oxygen species, the experiments were undertaken in the presence and absence of Cr in soils. The results indicated that the action of oxidative inhibitor enzymes increased significantly in roots as compared to shoots with increasing concentration of Cr in overburden soil. Higher concentration of Cr in soils inhibited the enzyme activity both in roots and shoots. The level of ROS in plants also enhanced with the increase in the concentration of Cr in the soil. In order to control the oxidative damage in plants, lemon grass can be considered defensive in nature to build up the antioxidant system which can scavenge the reactive oxygen species (ROS). Highlights • Lemon grass has antioxidative defense system to cope up with oxidative damage induced by Cr. • Oil, Citral-a, and Citral-b content of lemon grass leave increased with increase in the soil chromium concentration up to a certain limit. • The level of reactive oxygen species (ROS) in plants also enhanced with rise in the concentration of chromium in soil. • The lemon grass plants can propagate in Cr rich over burden soil without significant negative effects on plant growth and oil quality and quantity. • The fibrous root system of lemon grass plants helps for bioaccumulation of Cr from contaminated soils through its rhizofiltration activity. [ABSTRACT FROM AUTHOR]

A pot experiment was performed to examine the role of foliar applied mannitol (M) in chromium (Cr) stress alleviation in different maize cultivars. Two maize cultivars, one tolerant (6103) and one sensitive (9108) to chromium stress, were grown in soil treated with three concentrations of Cr (0, 5, and 10 mg kg−1) and three levels of mannitol (0, 50, and 100 mg L−1). Chromium stress decreased the overall growth of plants by reducing the plant height, root/shoot dry weight, chlorophyll contents, and enzymatic activities, while exacerbated the severity of reactive oxygen species in both maize cultivars. Chromium-induced reduction in growth attributes of maize plants was relatively higher in sensitive cultivar than that of tolerant one. Uptake of Cr by the plants and its translocation from roots to shoots increased with increasing concentration in the soil. However, foliar application of mannitol significantly alleviated the Cr stress and improved growth, biomass, and photosynthetic pigments of maize plants. Mannitol also considerably reduced Cr contents in leaves and roots of both cultivars. Hence, it is concluded that mannitol can be helpful for crops grown on heavy metal, especially Cr, contaminated soils for remediation purpose. [ABSTRACT FROM AUTHOR]

In order to verify if the magnetic parameters can be indicators of soil contamination, the relationship between magnetic parameters and the concentration of heavy metals in soil samples from the Almendares-Vento basin was studied. Measurements of magnetic susceptibility, chemical determinations of heavy elements and remanent magnetization, were made. The concentration values in the samples of the heavy elements (Cr, Fe, Ni, Mn, Cu, Zn and Pb) were determined by mass spectrometry with inductively coupled plasma. Magnetic susceptibility yielded higher values towards the upper part of the soil, up to 20 cm deep, which can be attributed to the presence of magnetic material of anthropogenic origin on the soil surface, generated by productive processes at the facilities of the region. It is concluded that increases in the values of magnetic susceptibility are indicators of the increase in the concentration levels of heavy elements for soils of the basin as a consequence of human contamination. [ABSTRACT FROM AUTHOR]

Abstract In this research, mechanochemical reduction was carried out to remediate Cr(VI) contaminated soil, and the reduction effectiveness was evaluated by analyzing the corresponding leachable fraction obtained through the toxicity characteristic leaching procedure (TCLP) proposed by the EPA. The results indicated that mechanochemical reduction can efficiently reduce the Cr(VI) concentration in the leachate. Under a milling time of 2 h, milling speed of 500 rpm, ball-to-powder weight ratio of 14 and Na 2 S dosage of 5%, the Cr(VI) leaching concentration significantly decreased from 663.98 mg L−1 to 0.84 mg L−1, much lower than the regulatory limit of 5 mg L−1. In addition, the significant decrease in Cr(VI) was mainly due to the reduction of Cr(VI) to Cr(III), as supported by X-ray photoelectron spectroscopy (XPS). The mechanochemical reduction with mechanism proposed in this experiment may involve two major processes: solidification and reduction (stabilization). Graphical abstract Image Highlights • Mechanochemical reduction was applied for the remediation of Cr (Ⅵ) contaminated soil with Na 2 S. • Mechanochemical reaction between Cr (Ⅵ) in contaminated soil and Na 2 S occurred. • After treatment, leachable Cr (Ⅵ) concentrations reduced and be lower than 5 mg L−1. • Mechanochemical reduction technique is promising for Cr (Ⅵ) contaminated soil remediation. [ABSTRACT FROM AUTHOR]

The retention behavior of three toxic chemicals, As, Cr and B, was investigated for an outcropping rock formation, the Albian Tégulines Clay (France, Aube). At a shallow depth, Tégulines Clay is affected by weathering processes leading to contrasted geochemical conditions with depth. One of the main features of the weathering is the occurrence of a redox transition zone near the surface. Batch sorption experiments of As(V), As(III), Cr(VI) and B were performed on samples collected at two depths representative either of oxidized or reduced mineral assemblages. Batch sorption experiments highlighted a distinct behavior between As, Cr and B oxyanions. Cr(VI) retention behavior was dominated by redox phenomena, notably its reduction to Cr(III). The in-situ redox state of the Tégulines Clay samples has a significant effect on Cr retention. On the contrary, As(V) reduction into As(III) is moderate and its retention slightly affected by the in-situ redox state of the Tégulines Clay. As(V) retention is higher than As(III) retention in agreement with literature data. B retention is strongly related to its natural abundance in the Tégulines clay samples. Distribution coefficient of B corrected from its natural content is expected to be very low for in-situ conditions. Finally, the retention and mobility of these oxyanions were affected by clay mineralogy, natural abundance, and reducing capacity of the Tegulines Clay. [ABSTRACT FROM AUTHOR]

Abstract One of the main problems of the industrialized world is the accumulation of chromium (Cr) in soil, which is a serious threat to the crops. Complete removal of Cr from the contaminated soils poses a great challenge. However, this issue can be minimised by using plant growth promoting microbes as a bioremediation tool. In the present study, healthy plants established near the University campus in Mardan were selected for the isolation of Cr resistant endophytes. From the designated plants, 114 species of endophytic fungi were isolated. Among the 114 isolated strains, 4 strains have induced resistance in L. sativa against Cr. The strains were identified as Aspergillus fumigatus , Rhizopus sp. , Penicillium radicum and Fusarium proliferatum based on ITS region (18 S rDNA) homology. The isolates have removed Cr from soil and culture media as well as bio-transformed it from highly toxic hexavalent to least toxic trivalent form, thus helped the Cr stressed L. sativa to restore its normal growth. The Rhizopus Sp. CUC23 has mainly accrued Cr and detoxified intracellularly, whereas A. fumigatus ML43 and P. radicum PL17 has detoxified up to 95% of Cr extracellularly. From the results, it is concluded that the selected endophytic strains might be used as biofertilizer for healthy and safe crop production in Cr contaminated soils. Graphical abstract Image 1 Highlights • Detoxification of hexavalent chromium by endophytic fungi in plant and soil has been reported. • Four selected fungal endophytes alleviated Cr toxicity in Lactuca sativa L. • The strains were able to carry out intra and extra mycelial reduction of Cr-VI to Cr-III • Translocation of Cr to the edible parts was significantly reduced in endophytes associated seedlings. [ABSTRACT FROM AUTHOR]

Using batch-type experiments, chromium (Cr(VI)) and fluoride (F − ) sorption/desorption were studied in forest and vineyard soil samples, pyritic material, pine bark, oak ash, hemp waste and mussel shell, as well as on samples of forest and vineyard soil, and of pyritic material, individually treated with 48 t ha −1 of pine bark, oak ash, and mussel shell. Pine bark showed the highest Cr(VI) sorption (always > 97% of the concentration added) and low desorption (<1.5%). Pyritic material sorbed between 55 and 98%, and desorbed between 0.6 and 9%. Forest and vineyard soils, oak ash, mussel shell and hemp waste showed Cr(VI) sorption always < 32%, and desorption between 22 and 100%. Pine bark also showed the highest F − retention (sorption between 62 and 73%, desorption between 10 and 15%), followed by oak ash (sorption 60–69%, desorption 11–14%), forest soil (sorption 60–73%, desorption 19–36%), and pyritic material (sorption 60–67%, desorption 13–15%), whereas in vineyard sorption was 49–64%, and desorption 24–27%, and in hemp waste sorption was 26–36%, and desorption 41–59%. Sorption data showed better fitting to the Freundlich than to the Langmuir model, especially in the case of Cr(VI), indicating that multilayer sorption dominated. The addition of by-products to the forest and vineyard soils, and to the pyritic material, caused an overall increase in F − sorption, and decreased desorption. Furthermore, the pine bark amendment resulted in increases in Cr(VI) retention by both soils and the pyritic material. These results could be useful to favor the recycling of the by-products studied, aiding in the management of soils and degraded areas affected by Cr(VI) and F − pollution, and in the removal of both anions from polluted waters. [ABSTRACT FROM AUTHOR]

Precise measurement of soil organic carbon (SOC) is essential for constructing regional inventories, developing best agricultural management practices, and modeling purposes. Currently, the automated dry combustion method is considered standard, but the method is both costly and time-consuming. There is a need for a simple, easy to use and cost-effective method of organic C determination in soil. A simple method of total organic carbon (TOC) determination in soil that involved wet digestion of K2Cr2O7-H2SO4-soil mixture in a commercial microwave oven followed by spectrophotomteric measurement of Cr (III) was evaluated. The method was compared with automated dry combustion and two other wet digestion methods. The method showed close agreement with dry combustion method (R2 = 0.90; root mean square error = 0.70) and the TOC measured with the two methods did not differ for a range of soils drawn from lowland and upland land-uses and varying in pH (6.2-9.3), TOC (2.8-14 g kg−1), and calcium carbonate content (0-6.7%). The recovery of the added organic C by the microwave method was 98.6 ± 4.2%. The results suggested that microwave-spectrophotometric method could be easily adopted in routine soil analysis as it is not only precise, rapid, and cost-effective but also produced small volume of reagent waste. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate Cr toxicity in young plants of the CCN 51 Theobroma cacao genotype at different concentrations of Cr 3+ in the soil (0, 100, 200, 400 and 600 mg kg −1 ) through physiological, ultrastructural, antioxidant and molecular changes. Doses of 400 and 600 mg Cr 3+ kg −1 soil severely affected foliar gas exchange, promoted by damages in photosynthetic machinery evidenced by the decrease in CO 2 fixation. Decreased expression of psbA and psbO genes, changes in enzymatic activity and lipid peroxidation also affected leaf gas exchange. A hormesis effect was observed at 100 mg Cr 3+ kg −1 soil for the photosynthetic activity. As a metal exclusion response, the roots of the cocoa plants immobilized, on average, 75% of the total Cr absorbed. Ultrastructural changes in leaf mesophyll and roots, with destruction of mitochondria, plasmolysis and formation of vesicles, were related to the oxidative stress promoted by excess ROS. The activity of the antioxidant enzymes SOD, APX, GPX and CAT and the amino acid proline coincided with the greater expression of the sod cyt gene demonstrating synchronicity in the elimination of ROS. It was concluded, therefore, that the tolerance of the cocoa plants to the toxicity of Cr 3+ depends on the concentration and time of exposure to the metal. Higher doses of Cr 3+ in the soil promoted irreversible damage to the photosynthetic machinery and the cellular ultrastructure, interfering in the enzymatic and non-enzymatic systems related to oxidative stress and gene expression. However, the low mobility of the metal to the leaf is presented as a strategy of tolerance to Cr 3+ . [ABSTRACT FROM AUTHOR]

The chromium pollution is serious problem in China. The objective of this study is detoxification of chromium contaminated soil with fly ash at high temperatures, and obtain the pottery products in order to realize the utilization of r Cr(VI)esources. The parameters of leaching concentration and ceramsite particle strength were selected to optimize the roasting parameters of ceramsite preparation by using single factor test. The optimum ceramsite products were obtained by orthogonal test. The effect mechanism of sintering process conditions on the properties of ceramsite was analyzed. The results shown that (1) the Ceramsite Cr(VI) has achieved the good solidification stabilization effect under the test condition; (2) the sintering temperature affect the ceramsite particle strength, apparent density, 1h water absorption rate at significant level; (3) the optimum sintering process condition is the 25% fly ash addition quantity, with the 1 120 °C sintering temperature and the 10 min sintering time; (4) the final ceramsite products belongs to the ordinary lightweight aggregate with packing density of 600 kg/m³, and barrel compressive strength of 3.0 MPa; (5) the concentration of Ceramsite Cr(VI) is 0.042 mg/L, and the total chromium concentration of the leaching liquid is 0.045 mg/L. The safety performance accord with the technical code for environmental protection of chromium residue pollution control (HJ/T301) for the treatment of concrete aggregates with chromium-contaminated soil after detoxification. [ABSTRACT FROM AUTHOR]

A soil–plant biological system was developed from chromium (Cr) polluted soil treated by the compost-phytoremediation method. The transformation and migration of the Cr in this system is comprehensively studied in this research. The results illustrated that the co-composting treatment can reduce the Cr availability from 39% (F1 was about 31% of total, F2 was about 8% of total) to less than 2% by stabilizing the Cr. However, herbaceous plants can accumulate the concentrations of Cr from 113.8 to 265.2 mg/kg in the two crops, even though the concentration of soluble Cr in the substrate soil was below 0.1 mg/L. Cr can be assimilated and easily transferred in the tissues of plants because the low-molecular-weight organic-acids (LMWOAs) derived from the plant root increase the bioavailability of Cr. The amount of extracted Cr dramatically increased when the organic acids were substituted in this order: citric acid > malic acid > tartaric acid > oxalic acid > acetic acid. On average the maximum (147.4 mg/kg) and the minimum (78.75 mg/kg) Cr were extracted by 20 mmol/L citric acid and acetic acid, respectively. The desorption of Cr in different acid solutions can be predicted by the pseudo second-order kinetics. The exchangeable Cr, carbonate-bound Cr, and residual Cr decreased, while Fe–Mn oxide bound Cr and organic bound Cr increased in the soil solid phase. According to the experimental results, the organic acids will promote the desorption and chelation processes of Cr, leading to the remobilization of Cr in the soil. [ABSTRACT FROM AUTHOR]

Even though the Amazon region is widely studied, there is still a gap regarding Cr exposure and its risk to human health. The objectives of this study were to 1) determine Cr concentrations in seven chemical fractions and 6 particle sizes in Amazon soils, 2) quantify hexavalent Cr (CrVI) concentrations using an alkaline extraction, 3) determine the oral and lung bioaccessible Cr, and 4) assess Cr exposure risks based on total and bioaccessible Cr in soils. The total Cr in both A (0–20 cm) and B (80–100 cm) horizons was high at 2346 and 1864 mg kg −1 . However, sequential extraction indicated that available Cr fraction was low compared to total Cr, with Cr in the residual fraction being the highest (74–76%). There was little difference in total Cr concentrations among particle sizes. Hexavalent Cr concentration was also low, averaging 0.72 and 2.05 mg kg −1 in A and B horizon. In addition, both gastrointestinal (21–22 mg kg −1 ) and lung (0.95–1.25 mg kg −1 ) bioaccessible Cr were low (<1.2%). The low bioavailability of soil Cr and its uniform distribution in different particle sizes indicated that Cr was probably of geogenic origin. Exposure based on total Cr resulted in daily intake > the oral reference dose for children, but not when using CrVI or bioaccessible Cr. The data indicated that it is important to consider both Cr speciation and bioaccessibility when evaluating risk from Cr in Amazon soils. [ABSTRACT FROM AUTHOR]

The purpose of this research is to design a new bioremediation-electrokinetic (Bio-EK) remediation process to increase treatment efficiency of chromium contamination in soil. Upon residual chromium analysis, it is shown that traditional electrokinetic-PRB system (control) does not have high efficiency (80.26%) to remove Cr(VI). Bio-electrokinetics of exogenous add with reduction bacteria Microbacterium sp. Y2 and electrokinetics can enhance treatment efficiency Cr(VI) to 90.67% after 8 days’ remediation. To optimize the overall performance, integrated bio-electrokinetics were designed by synergy with 200 g humic substances (HS) into the systems. According to our results, Cr(VI) (98.33%) was effectively removed via electrokinetics. Moreover, bacteria and humic substances are natural, sustainable, and economical enhancement agents. The research results indicated that the use of integrated bio-electrokinetics is an effective method to remediate chromium-contaminated soils. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are symbionts in roots of 70–90% of terrestrial plants, and are present even in highly perturbed sites like soils polluted with potentially toxic elements (PTE). Plants and indigenous AMF present in polluted soils may play an important role in PTE uptake (phytoextraction) and complexation (phytostabilization). The present work was addressed to: i) analyze the spore community structure of AMF associated to Ricinus communis rhizospheres from a chromium (Cr) polluted site (MOR) and a non-Cr polluted site (PAR); ii) analyze whether plant growth and mycorrhizal colonization of R. communis , and Cr(VI) remaining concentration in soil, differed in both rhizosphere soils when exposed to a mixture of Cr(III)/Cr(VI) polluting concentration in a greenhouse experiment. Culture trap from both rhizosphere soil were established previously to the study to propagate AMF. The community structure was analyzed with morphological and molecular approaches. The spore community structure differed in MOR as related to PAR rhizosphere soils: Acaulosporaceae and Gigasporaceae morphotypes were only observed in PAR and Paraglomeraceae ribotypes were detected only in MOR. Finally, a greenhouse experiment was designed to study the response of both communities when grown in association with R. communis and exposed to polluting concentrations of Cr(III)/Cr(VI) (250/8 μg g − 1 soil d.w.). The mycorrhizal colonization was higher in roots grown in presence of MOR than in presence of PAR AMF community, exposed or not to Cr, and the final Cr(VI) concentration in soil was lower in the pots with MOR AMF community than in the pots with PAR AMF community (6.9 ± 0.2 and 14.3 ± 1.5 μg Cr(VI) g − 1 soil d.w., respectively). Our results suggest that the previous exposure to polluting concentration of Cr could have selected AMF species with a higher infectivity and thus more likely to better contribute to reduce the pollutant concentration in the soil. [ABSTRACT FROM AUTHOR]

Chromium (Cr) accumulation in soil and plants has been reported after successive applications of tannery sludge, which is a matter of concern because Cr can promote environmental contamination and affect the food chain. In this study, we evaluated the growth of and Cr accumulation in maize and cowpea after seven years of consecutive applications of composted tannery sludge (CTS) under field conditions. The experiment consisted of application of CTS at five levels: 0 (control), 2.5, 5, 10, and 20 Mg ha-1 (dry basis). The growth of and Cr accumulation in maize and cowpea were evaluated at 75 and 65 days after plant emergence, respectively. CTS application increased the shoot biomass of maize and cowpea. Accumulation of Cr was similar for both plant species, with higher accumulation in roots. However, Cr accumulation in grains differed as the CTS doses increased; cowpea accumulated more Cr while maize did not accumulate more Cr in grains with higher CTS doses. In conclusion, application of CTS led to higher growth of maize and cowpea plants, and both species exhibited similar Cr accumulation in roots and shoots. [ABSTRACT FROM AUTHOR]

Strains G1 ( Geotrichum sp.) and B2 ( Bacillus sp.) were isolated from a hexavalent chromium (Cr(VI)) contaminated site and they could remove Cr(VI) efficiently. The mixed culture of G1 and B2 (1:1, v/v) was prepared to test remediation of Cr(VI) contaminated soil. The influences of pH, magnetic field, dissolved oxygen, carbon sources and solid/liquid ratio on Cr(VI) removal were investigated, as well as the effects of pH and magnetic field on Cr(VI) desorption. The results indicated that the desorption of Cr(VI) from the contaminated soil was strongly affected by pH of the leaching solution with optimal value of 7.0 based on the growth of both microorganisms and desorption efficiency. Weak magnetic field of 7.0 mT promoted both the Cr(VI) desorption and the growth of G1. Compared with anaerobic conditions, bioreduction rate of Cr(VI) under aerobic conditions was higher. The optimal carbon source and solid/liquid ratio were glucose (5 g l −1 ) and 1/15 (w/v), respectively. The associated Cr(VI) reduction efficiency was 94.8%, which was 68.8% higher than control. The high bioremediation efficiency of the mixed cultures of G1 and B2 could be attributed to their alternative growth patterns to enhance the performance of bioremediation of the heavy metals contaminated sites. [ABSTRACT FROM AUTHOR]

Four different mercaptoalkyl-substituted calixarene derivatives (5,11,17,23-tetra-tert-butyl-25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(5-mercaptopentanoxyl)-26,28-dihydroxycalix[4]arene and 5,17-di-tert-butyl-11,23-di-carboxyl-26,28-bis(3-mercaptopropoxyl)-25,27-di-hydroxycalix[4]arene) were synthesized. Their structures were characterized by Fourier transform infrared spectroscopy (FTIR),1H and13C NMR spectroscopy, and elemental analysis techniques. Moreover, their extraction capabilities at different parameters such as pH, shaking speed, and shaking time were examined toward dichromate ions. Results implied that all mercaptoalkyl-substituted calixarene derivatives showed an extraction capability toward dichromate anion while the carboxyl-functionalized calixarene-marcapto-alkyl derivative exhibited the highest extraction capability. [ABSTRACT FROM AUTHOR]

It has been well demonstrated that arbuscular mycorrhizal (AM) symbiosis can improve plant chromium (Cr) tolerance, but the detoxification mechanisms are still unsolved. In the present study the role of AM symbiosis in plant sulfur (S) acquisition and metabolism related to Cr detoxification was investigated. Medicago truncatula plants were cultivated with/without AM fungus Rhizophagus irregularis in Cr(VI) contaminated soils at two soil S and phosphorus (P) concentrations. Sulfur uptake, transport and metabolism by plants were determined by biochemical and molecular methods. Meanwhile, Cr uptake and transformation were characterized by using spectroscopic methods, including synchrotron based X-ray absorption near edge structure (XANES) analysis. The results indicated that mycorrhizal inoculation improved plant S acquisition by up-regulating the expression of high affinity sulfate transporter genes (i.e. MtSULTR1.1 , MtSULTR1.2 ) in plant roots. Mycorrhizal colonization also systematically regulated S transport and metabolism for Cr(VI) detoxification. XANES analysis revealed the Cr immobilization in AM roots by phosphate and histidine-like ligands rather than thiol groups. Correlation analysis further confirmed possible involvement of S metabolites in the relief of Cr induced oxidative stress. Mycorrhizal effects were more pronounced under low P condition. The study allowed a new insight into the mechanisms of enhanced plant Cr tolerance by AM symbiosis. [ABSTRACT FROM AUTHOR]

Purpose: This study was focused on co-composting of Cr(VI)-contaminated soil with three different biomass solid wastes for immobilizing Cr(VI).Materials and methods: Sequential chemical extraction of the soil was performed to determine Cr fractions changing over time during the compost process. Fluorescence spectroscopy was applied to study the composition and evolution characteristics of organic matter from the municipal sludge and Cr(VI)-contaminated co-composting. The influence of organic matter evolution on the bioavailability of Cr by multivariate statistical analysis was further investigated.Results and discussion: Results proved that the Cr(VI)-contaminated soil can be co-composted successfully and this practice results in significant shifts in Cr availability. The concentrations of non-available fractions increased as well as available fractions decreased during the composting stage. The results from the Pearson correlation analysis showed positive relation between non-available fractions and TOC and negative relation between organic matter-bound fraction and TOC. Furthermore, principal factor analysis among Cr and organic matter indicated that the available fractions Cr were bound with humic-like substances and their bioavailability was low.Conclusions: It can be concluded that co-composting provides a method for remediating Cr(VI)-contaminated soil through the decrease of bioavailability of Cr and the binding between available fractions Cr and humic-like substances. [ABSTRACT FROM AUTHOR]

Purpose: Remediation of heavy metals by reducing their mobility and bioavailability without removing them from soils is considered to be a cost-effective and an efficient method to address their toxicity for living organisms and soil health. The main objectives of the current study, therefore, were to investigate the potential of sugarcane bagasse biochar in reducing the bioavailability of soil cadmium (Cd) and chromium (Cr) and assessing the impact of biochar application on soil microbial activities and plant growth in metal-contaminated soil.Materials and methods: Air-dried soil was artificially spiked with Cd and Cr metals by using Cd(NO3)2 and Cr(NO3)2 solutions. Biochar was homogenously mixed in metal-spiked soil. The experimental spiked soil was categorized as with and without biochar-amended soil. Mash bean crop was used as test plant. After crop harvesting, soil Cd and Cr were extracted by diethylenetriaminepentaacetic acid (DTPA) to estimate the mobility of heavy metals. Furthermore, the plant metal contents, microbial biomass carbon, urease activity, dehydrogenase (DHA) activity, total organic carbon, and plant biomass were determined. The Langmuir adsorption isotherms were studied for Cd and Cr in unamended soil, biochar-amended soil, and biochar only. The electronegative charges of biochar and biochar-amended soil were also measured using the zeta potential.Results and discussion: The results show that the application of biochar to Cr- and Cd-contaminated soil significantly reduced their availability by 85 and 63%, respectively. The application of biochar at 15 g kg−1 prominently reduced the extractable Cd contents by 29 and 32% in Cd-contaminated and Cr–Cd-contaminated soils, respectively. The Cr concentration in the plant decreased by 34 and 41% in Cr-contaminated and Cr–Cd-contaminated soil compared with spiked soil without biochar. The Langmuir model achieved the best fit; its isotherm predicted the biochar’s maximum adsorption capacity for Cd (0.42 mg g−1) and Cr (0.35 mg g−1). Biochar incorporation in Cd–Cr-contaminated soil significantly increased the microbial activity and mash bean biomass.Conclusions: Our findings indicate that the addition of sugarcane bagasse-derived biochar significantly reduces the Cd and Cr availability in single and co-contaminated soil. In addition, an increase in the microbial activity and plant growth and a significant reduction in the Cd and Cr uptake by mash bean are possible after biochar addition. [ABSTRACT FROM AUTHOR]

Contamination of soil is a major problem globally with colligated danger for ecosystem and human health. Chromium (Cr) is a toxic heavy metal and caused harmful effect on growth and development of plants. Phytostabilization reduced the mobility of heavy metals with addition of amendments which can significantly decrease metal solubility in soil. Phytostabilization can be achieved by application of biogas slurry (BGS) and endophytic bacteria as amendments in the contaminated soils. The present study revealed that the Burkholderia phytofirmans PsJN and BGS improved the growth, physiology, and antioxidant activity and reduced Cr uptake under a pot experiment spiked with Cr (20 mg kg−1 soil). The experiment was designed under completely randomized design, four treatments with three replications in normal and Cr-contaminated soil. The inoculation of endophytic bacteria improved the growth and physiology of Brassica. This study showed that the inoculation of endophytic bacteria stabilized the Cr levels in soil and minimized the uptake by the plant shoots and roots in BGS-amended soil. Similarly, activity of antioxidants such as catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), and glutathione s-transferase (GST) was decreased to normal with combined treatment of BGS and endophytic bacteria in Cr-stressed soil. Overall, the best results were analyzed by combined treatment of BGS and endophytic bacteria to improve growth, physiology, and antioxidant activity of Brassica and immobilize Cr in soil. Moreover, results emphasized the need to use BGS alone or in combination with endophytic bacteria to optimize crop performance, stabilize Cr concentration, and improve environmental efficiency. [ABSTRACT FROM AUTHOR]

Clay minerals could reduce Cr(VI) to Cr(III) in the soil, but the mechanisms and influential factors for the reduction reaction have not been clearly reported. In this study, it was hypothesized that the Fe(II) released from the clay minerals or adsorbed on the clay surface plays a crucial role in the reduction of Cr(VI). The Fe(II) released from clay minerals reduced Cr(VI) rapidly in the aqueous phase at the initial stage, and the amount of Fe(II) in the aqueous phase was directly proportional to the amount of Cr(VI) reduced. Cr(VI) was then reduced gradually by the Fe(II) adsorbed on the clay minerals. XPS analysis confirmed the change of Fe speciation on the surface of the clay minerals. Therefore, we concluded that the reduction in Cr(VI) by the clay minerals was due to the Fe in the clay minerals. [ABSTRACT FROM AUTHOR]

In this study, an effort was made to identify an efficient phosphate solubilizing bacterial strain from chromium contaminated agricultural soils. Based on the formation of a solubilized halo around the colonies on Pikovskaya's agar amended with chromium (VI), 10 strains were initially screened out. Out of 10, strain CPSB4, which showed significantly high solubilization zone at different chromium concentrations, was selected for further study. The strain CPSB4 showed significant plant growth promotion traits with chromium (VI) stress under in-vitro conditions in broth. The plant growth promotion activities of the strain decreased regularly, but were not completely lost with the increase in concentration of chromium up to 200 mg L −1 . On subjected to FT-IR analysis, the presence of the functional group, indicating the organic acid aiding in phosphate solubilization was identified. At an optimal temperature of 30 ° C and pH 7.0, the strain showed around 93% chromium (VI) reduction under in-vitro conditions in broth study. In soil condition, the maximum chromium (VI) reduction obtained was 95% under in-vitro conditions. The strain CPSB4 was identified as Klebsiella sp. on the basis of morphological, biochemical and 16S rRNA gene sequencing. This study shows that the diverse role of the bacterial strain CPSB4 would be useful in the chromium contaminated soil as a good bioremediation and plant growth promoting agent as well. [ABSTRACT FROM AUTHOR]

The present work focused on analyzing the effects of solar energy on the electrokinetic remediation (EKR) of Cr-contaminated soil, compared to direct current (DC) power supply. Meanwhile, to control the remedied soil pH and focusing phenomena, the exchange electrode-EKR (EE-EKR) has also been employed. Four runs of tests were conducted using DC power supply with the conventional EKR (run A, run D), DC power supply with EE-EKR (run B) and solar energy with EE-EKR (run C) respectively. Important electrokinetic parameters such as electrical voltage and current, electroosmotic flow, soil pH, the remediation efficiency of total Cr, Cr(VI), Cr(III) and cost analysis were investigated to evaluate EE-EKR using solar energy. The results show that run B had the highest removal efficiency of total Cr (43.65%), Cr(VI) (91.88%), and Cr(III) (19.32%), and run C, run A, run D follow in turn. It was proved that EE-EKR could increase the removal efficiency of Cr, especially Cr(III) from contaminated soil, because it could reduce focusing phenomena and enhance electrical current. Meanwhile, the experimental results also indicated that the combination of electrokinetics and solar energy was feasible and effective to some extent for the remediation of Cr-contaminated soil. [ABSTRACT FROM AUTHOR]

Electrokinetic (EK) remediation has potential to simultaneously remove heavy metals (HMs) and organic compounds from soil, but removal efficiency of these pollutants is very low in general if no enhancing treatment is applied. In this work, a new enhanced EK remediation technology to decontaminate a HM-organic cross-contaminated soil by applying different surfactants and pH control were studied. Laboratory-scale EK experiments were performed using different surfactants (Triton X-100, Tween 80, and Dowfax 8390) and controlling catholyte electrolyte pH at 4. Diphenylcarbazide (DPC), which is a complexing agent used in the spectrophotometric determination of chromate, was used as a solubilizer for chromium (Cr). After treatment with 1.0 V/cm of voltage gradient for 15 days, soil pH, electroosmotic flow (EOF), electrical current, and the concentrations and chemical fractionations of soil phenanthrene (PHE) and Cr were analyzed. Results indicated that EOF rate in the Dowfax 8390 system was higher than other surfactants. Using EK technology for removal of Cr and PHE in the presence of Dowfax 8390 was more efficient than in the presence of other surfactants. A surfactant system containing both Dowfax 8390 and solubilized DPC is the most effective surfactant system to remediate Cr-contaminated soil in EK treatment. However, to a certain extent, the removal efficiency of PHE is reduced. In addition, the influence of pH in this system was evaluated. Under the optimal operating conditions, more than 70%, 86%, and 56% of Cr(T), Cr6+, and PHE were removed from the soil, respectively. Overall, it can be concluded that the enhanced EK remediation system in the simulated setup can be effective for the removal of both HMs and polycyclic aromatic hydrocarbons from clayey soils and will help develop the remediation technology for HM-organic cross-contaminated soil. [ABSTRACT FROM AUTHOR]

Purpose: Chromium, a potentially harmful element, occurs commonly within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid-phase chemical speciation of Cr and its environmental mobility. In this study, we adopt an integrated geochemical approach to investigate and determine the long-term fate of Cr in the urban sediment cascade. Materials and methods: We use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation, geochemical characteristics and potential long-term behaviour of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Results and discussion: Cr-bearing grains within RDS and aquatic sediment are predominantly iron oxides and alumino-silicate glass grains. Electron microprobe analysis indicates Cr concentrations up to 3300 and 133,400 μg g in the RDS and aquatic grains, respectively. XANES analysis indicates that Cr(III) is the dominant oxidation state, with only trace amounts of Cr(VI). Importantly, Cr speciation does not appear to have changed between sedimentary environments and the dominance of Cr(III) suggests limited bioavailability or toxicity under predominant environmental (anoxic and neutral pH) conditions in the aquatic sediment sink. Furthermore, geochemical analyses suggest the environmental mobility of Cr in the aquatic sediment sink is low (compared to other toxic metals) due to its association mainly with alumino-silicate glass grains and its inclusion as an integral part of the glass structure. Conclusions: Industrial glass grains are a major component of urban sediment worldwide. The speciation and geochemical investigations performed in this study suggest most Cr within the urban sediment cascade may be resistant to environmental processes that could mobilise other toxic metals. [ABSTRACT FROM AUTHOR]

In this study, a highly stable nanoscale zero-valent iron composite (HS-NZVI) was obtained via modifying nanoscale zero-valent iron (NZVI) with tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMOS), and used for Cr(VI) remediation in aqueous solution. The obtained HS-NZVI remained stable in water without being oxidized for over 12 h. After four consecutive runs, the Cr(VI) removal efficiency of HS-NZVI maintained a value of more than 82%. Moreover, the Cr(VI) removal capacity per unit weight of NZVI in HS-NZVI reached 292.8 mg/g within 60 min at the initial Cr(VI) concentration of 120 mg/L at pH 5. The Cr(VI) removal efficiency of HS-NZVI increased with decreasing solution pH, and the experimental data for Cr(VI) removal by HS-NZVI were well-described by the pseudo-first-order reaction model. Additionally, scanning electron microscope (SEM) images, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) measurements of the product after reaction revealed that the mechanism of Cr(VI) remediation by HS-NZVI mainly involved adsorption, reduction and co-precipitation. Considering the advantages of easy preparation, excellent stability and reusability, and high Cr(VI) removal capacity as well as the magnetic recovery property, HS-NZVI is expected to have notably promising applications for the remediation of Cr(VI) contaminated sites. [ABSTRACT FROM AUTHOR]

Kasur is one of the hubs of leather industry in the Punjab, Pakistan, where chrome tanning method of leather processing is extensively being used. Chromium (Cr) accumulation levels in the irrigation water, soil, and seasonal vegetables were studied in three villages located in the vicinity of wastewater treatment plant and solid waste dumping site operated by the Kasur Tanneries Waste Management Agency (KTWMA). The data was interpreted using analysis of variance (ANOVA), clustering analysis (CA), and principal component analysis (PCA). Interpolated surface maps for Cr were generated using the actual data obtained for the 30 sampling sites in each of the three villages for irrigation water, soil, and seasonal vegetables. The level of contamination in the three villages was directly proportional to their distance from KTWMA wastewater treatment plant and the direction of water runoff. The highest level of Cr contamination in soil (mg kg) was observed at Faqeeria Wala (37.67), intermediate at Dollay Wala (30.33), and the least in Maan (25.16). A gradational variation in Cr accumulation was observed in the three villages from contaminated wastewater having the least contamination level (2.02-4.40 mg L), to soil (25.16-37.67 mg kg), and ultimately in the seasonal vegetable crops (156.67-248.33 mg kg) cultivated in the region, having the highest level of Cr contamination above the permissible limit. The model used not only predicted the current situation of Cr contamination in the three villages but also indicated the trend of magnification of Cr contamination from irrigation water to soil and to the base of the food chain. Among the multiple causes of Cr contamination of vegetables, soil irrigation with contaminated groundwater was observed to be the dominant one. [ABSTRACT FROM AUTHOR]

Chromium (Cr) is a biologically non-essential, carcinogenic and toxic heavy metal. The cultivation of Cr-tolerant genotypes seems the most favorable and environment friendly strategy for rehabilitation and remediation of Cr-contaminated soils. To prove this hypothesis and identify the Cr tolerance, the present study was performed to assess the physiological and biochemical response of sunflower genotypes to Cr stress. The seeds of six sunflower hybrids, namely FH-425, FH-600, FH-612, FH-614, FH-619, and FH-620, were grown in spiked soil for 12 weeks under increasing concentrations of Cr (0, 5, 10, and 20 mg kg). A seed germination test was also run under different concentrations of Cr (0, 5, 10, 200 mM) in petri dishes. Plants were harvested after 12 weeks of germination. Different plant attributes such as growth; biomass; photosynthesis; gas exchange; activity of antioxidant enzymes, i.e., superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate (APX), and catalases (CAT); reactive oxygen species (ROS); lipid peroxidation; electrolyte leakage; and Cr concentration as well as accumulations in all plant parts were studied for the selection of the most Cr-tolerant genotype. Increasing concentration of Cr in soil triggered the reduction of all plant parameters in sunflower. Cr stress increased electrolyte leakage and production of reactive oxygen species which stimulated the activities of antioxidant enzymes and gas exchange attributes of sunflower. Chromium accumulation in the root and shoot increased gradually with increasing Cr treatments and caused reduction in overall plant growth. The accumulation of Cr was recorded in the order of FH-614 > FH-620 > FH-600 > FH-619 > FH-612 > FH-425. The differential uptake and accumulation of Cr by sunflower hybrids may be useful in selection and breeding for Cr-tolerant genotypes. [ABSTRACT FROM AUTHOR]

Chromium pollution of soil and water is a serious environmental concern due to potential carcinogenicity of hexavalent chromium [Cr(VI)] when ingested. Eucalyptus bark biochar (EBB), a carbonaceous black porous material obtained by pyrolysis of biomass at 500 °C under oxygen-free atmosphere, was used to investigate the removal of aqueous Cr(VI) upon interaction with the EBB, the dominant Cr(VI) removal mechanism(s), and the applicability to treat Cr(VI)-contaminated wastewater. Batch experiments showed complete removal of aqueous Cr(VI) at pH 1-2; sorption was negligible at pH 1, but ~55% of total Cr was sorbed onto the EBB surface at pH 2. Detailed investigations on unreacted and reacted EBB through Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry (XPS) indicate that the carboxylic groups in biochar played a dominant role in Cr(VI) sorption, whereas the phenolic groups were responsible for Cr(VI) reduction. The predominance of sorption-reduction mechanism was confirmed by XPS studies that indicated ~82% as Cr(III) and ~18% as Cr(VI) sorbed on the EBB surface. Significantly, Cr(VI) reduction was also facilitated by dissolved organic matter (DOM) extracted from biochar. This reduction was enhanced by the presence of biochar. Overall, the removal of Cr(VI) in the presence of biochar was affected by sorption due to electrostatic attraction, sorption-reduction mediated by surface organic complexes, and aqueous reduction by DOM. Relative dominance of the aqueous reduction mechanism depended on a critical biochar dosage for a given electrolyte pH and initial Cr(VI) concentration. The low-cost EBB developed here successfully removed all Cr(VI) in chrome tanning acidic wastewater and Cr(VI)-contaminated groundwater after pH adjustment, highlighting its potential applicability in effective Cr(VI) remediation. [ABSTRACT FROM AUTHOR]

The contamination of soils by metals such as arsenic, chromium, copper and organic compounds such as pentachlorophenol (PCP) and dioxins and furans (PCDD/F) is a major problem in industrialized countries. Excavation followed by disposal in an appropriate landfilling is usually used site to manage these contaminated soils. Many researches have been conducted to develop physical, biological, thermal and chemical methods to allow the rehabilitation of contaminated sites. Thermal treatments including thermal desorption seemed to be the most appropriate methods, allowing the removal of more than 99.99% of organic contaminants but, they are ineffective for inorganic compounds. Biological treatments have been developed to remove inorganic and hydrophobic organic contaminants but their applications are limited to soils contaminated by easily biodegradable organic compounds. Among the physical technologies available, attrition is the most commonly used technique for the rehabilitation of soils contaminated by both organic and inorganic contaminants. Chemical processes using acids, bases, redox agents and surfactants seemed to be an interesting option to simultaneously extract organic and inorganic contaminants from soils. This paper will provide an overview of the recent developments in the field of decontamination technologies applicable for the removal of As, Cr, Cu, PCP and/or PCDD/F from contaminated soils. [ABSTRACT FROM AUTHOR]

Biochar (BC) has been widely used as a low-cost adsorbent for the removal of contaminants from water and soil. However, the adsorption ability of BC towards heavy metal oxyanions (e.g., Cr(VI)) is relatively low due to the negatively charged surface of BC. In this study, pristine BC was impregnated with Fe3+to improve its Cr(VI) adsorption capability. Fe3+-impregnated BC (Fe3+-BC) was successfully synthesized by a simple impregnation method and used for the removal of Cr(VI) from aqueous solution. Various factors affecting the adsorption, such as impregnation ratio, pH, adsorbent dosage, contact time, temperature, and the presence of humic acid, were investigated in detail. Results showed that Fe3+-BC had strong adsorption ability to Cr(VI) with a maximum adsorption capacity of 197.80 mg/g, which were not only significantly higher than that of the pristine BC, but also were superior to many previously reported adsorbents. It was favorable for Cr(VI) adsorption under the condition of acidic and high temperature. The adsorption data obeyed Sips and Langmuir isotherms and the kinetic data were well described by the pseudo-first-order kinetic model. The results herein revealed that the Fe3+-impregnated BC had a good potential as a highly efficient material for adsorption of Cr(VI) from aqueous solution. [ABSTRACT FROM PUBLISHER]

Serpentinite soils, common throughout the world, are characterized by low calcium-to-magnesium ratios, low nutrient levels and elevated levels of heavy metals. Yet the water quality and heavy metal concentrations in sediments of streams draining serpentine geology have been little studied. The aim of this work was to collect baseline data on the water quality (for both wet and dry seasons) and metals in sediments at 11 sites on the Marlborough Creek system, which drains serpentine soils in coastal central Queensland, Australia. Water quality of the system was characterized by extremely hard waters (555-698 mg/L as CaCO), high dissolved salts (684-1285 mg/L), pH (8.3-9.1) and dissolved oxygen (often >110% saturation). Cationic dominance was Mg > Na > Ca > K and for anions HCO > Cl > SO. Al, Cu and Zn in stream waters were naturally high and exceeded Australian and New Zealand Environment and Conservation Council guidelines. Conductivity displayed the highest seasonal variability, decreasing significantly after wet season flows. There was little seasonal variation in pH, which often exceeded regional guidelines. Stream sediments were enriched with concentrations of Ni, Cr, Co and Zn up to 35, 21, 10 and 2 times the world average for shallow sediments, respectively. Concentrations for Ni and Cr were up to 60 and 16 times those of the relevant Interim Sediment Quality Guidelines Low Trigger Values, respectively. The distinctive nature of the water and sediment data suggests that it would be appropriate to establish more localized water quality and sediment guidelines for the creek system for the water quality parameters conductivity, Cu and Zn (and possibly Cr and Cd also), and for sediment concentrations of Cd, Cr and Ni. [ABSTRACT FROM AUTHOR]

Two native bacterial strains, FY1 and WZ2, that showed high chromium(VI)-reducing ability were respectively isolated from electroplating and tannery effluent–contaminated sites and identified asBacillusandArthrobacter. The objective of the present study was to evaluate their potential for future application in soil bioremediation. The results showed that bothBacillussp. FY1 andArthrobactersp. WZ2 were tolerant to 1000 mg L−1Cr(VI) and capable of reducing 78–85% and 75–82% of Cr(VI) (100–200 mg L−1) within 24 h, respectively. The Cr(VI) reduction rate decreased with increasing levels of Cr(VI) concentration (200–1000 mg L−1). The optimum pH, temperature, and inoculum concentration for Cr(VI) reduction were found to be between pH 7.0 and 8.0; 30 and 35°C; and 1 × 108cells ml−1, respectively. Further evidence for the bioremediation potential ofBacillussp. FY1 andArthrobacter sp. WZ2 was provided by the high capacity to reduce 100, 200, and 500 mg kg−1Cr(VI) in contaminated soil by 83–91%, 78–85%, and 71–78% within 7 days, respectively. These findings demonstrated the high potential ofBacillussp. FY1 andArthrobacter sp. WZ2 for application in future soil bioremediation. [ABSTRACT FROM AUTHOR]