Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L(-1) Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0-24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)-EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP-MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)-benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP-MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)-EDTA.     

On-line dynamic extraction and automated determination of readily bioavailable hexavalent chromium in solid substrates using micro-sequential injection bead-injection lab-on-valve hyphenated with electrothermal atomic absorption spectrometry

A novel and miniaturized micro-sequential injection bead-injection lab-on-valve (microSI-BI-LOV) fractionation system was developed for on-line microcolumn soil extraction under simulated environmental scenarios and accurate monitoring of the content of easily mobilisable hexavalent chromium in soil environments at the sub-low parts-per-million level. The flow system integrates dynamic leaching of hexavalent chromium using deionized water as recommended by the German Standard DIN 38414-S4 method; on-line pH adjustment of the extract by a 0.01 mol L(-1) Tris-HNO(3) buffer solution; isolation of the chromate leached from the matrix constituents onto a Q Sepharose strong anion-exchanger freshly packed into the microconduits of the microSI-assembly; air-segmented elution of the sorbed species by a 40 microL plug of 0.5 mol L(-1) NH(4)NO(3) (pH 8) eluent; and detection by electrothermal atomic absorption spectrometry (ETAAS). The effect of simulated acidic rain on the accessibility of chromate forms for plant uptake was also investigated. The proposed approach offers several advantages over conventional speciation/fractionation protocols in the batch mode, including immediate separation with concomitant preconcentration of the released chromate, minimization of Cr(vi) to Cr(iii) interconversion risks, enhanced accuracy, and non-existence of re-adsorption/re-distribution problems along with a detailed pattern of the kinetics of the leaching process. The reliability of the proposed method was evaluated via spiking of a moderately polluted agricultural soil material (San Joaquin Soil-Baseline Trace Element Concentrations) with water-soluble Cr(vi) salts at different concentration levels. The potential of the microSI-BI-LOV set-up with renewable surfaces for flame-AAS determination of high levels of readily bioavailable chromate in contaminated soils is also addressed.     

Solid-phase extraction of the chromium(III)-diphenylcarbazone complex prior to ion-pair chromatography and application to geological samples

A method for the pre-treatment of acid samples prior to ion chromatography is described. In a strong acid medium, Cr(VI) oxidizes diphenylcarbazide, the resulting products forming a stable complex which can be transferred in a methanolic medium by solid-phase extraction using polyethylene as sorbent. This methanolic sample solution can be injected directly into a chromatographic system with a silica-based column. The separation and determination of the chromium complex can be performed by HPLC-using a mobile phase of 15% (v/v) acetonitrile containing 1 mmol/L tetrabutyl ammonium hydroxide (TBAH). The detection limit is estimated to be 2 microg/L chromate and the linear range is at least 0.05-2 mg/L chromate.     

A biological process for the reclamation of flue gas desulfurization gypsum using mixed sulfate-reducing bacteria with inexpensive carbon sources

A combined chemical and biological process for the recycling of flue gas desulfurization (FGD) gypsum into calcium carbonate and elemental sulfur is demonstrated. In this process, a mixed culture of sulfate-reducing bacteria (SRB) utilizes inexpensive carbon sources, such as sewage digest or synthesis gas, to reduce FGD gypsum to hydrogen sulfide. The sulfide is then oxidized to elemental sulfur via reaction with ferric sulfate, and accumulating calcium ions are precipitated as calcium carbonate using carbon dioxide. Employing anaerobically digested municipal sewage sludge (AD-MSS) medium as a carbon source, SRBs in serum bottles demonstrated an FGD gypsum reduction rate of 8 mg/L/h (10⁹ cells)^-1. A chemostat with continuous addition of both AD-MSS media and gypsum exhibited sulfate reduction rates as high as 1.3 kg FGD gypsum/m³d. The increased biocatalyst density afforded by cell immobilization in a columnar reactor allowed a productivity of 152 mg SO₄ ^-2/Lh or 6.6 kg FGD gypsum/m³d. Both reactors demonstrated 100% conversion of sulfate, with 75–100% recovery of elemental sulfur and chemical oxygen demand utilization as high as 70%. Calcium carbonate was recovered from the reactor effluent on precipitation using carbon dioxide. It was demonstrated that SRBs may also use synthesis gas (CO, H₂, and CO₂ in the reduction of gypsum, further decreasing process costs. The formation of two marketable products—elemental sulfur and calcium carbonate—from FGD gypsum sludge, combined with the use of a low-cost carbon source and further improvements in reactor design, promises to offer an attractive alternative to the landfilling of FGD gypsum.

     

Solid-phase extraction of the chromium(III)-diphenylcarbazone complex prior to ion-pair chromatography and application to geological samples

A method for the pre-treatment of acid samples prior to ion chromatography is described. In a strong acid medium, Cr(VI) oxidizes diphenylcarbazide, the resulting products forming a stable complex which can be transferred in a methanolic medium by solid-phase extraction using polyethylene as sorbent. This methanolic sample solution can be injected directly into a chromatographic system with a silica-based column. The separation and determination of the chromium complex can be performed by HPLC-using a mobile phase of 15% (v/v) acetonitrile containing 1 mmol/L tetrabutyl ammonium hydroxide (TBAH). The detection limit is estimated to be 2 g/L chromate and the linear range is at least 0.05–2 mg/L chromate.     

Surface-mediated chromate-resistant mechanism of Enterobacter cloacae bacteria investigated by atomic force microscopy

The Enterobacter cloacae CYS-25 strain isolated from a chromate plant shows a strong capability for chromate resistance instead of chromate reduction in aerobic conditions. In this study, atomic force microscopy (AFM) was used for studying the morphology characteristics of bacterial properties during the chromate resistance process. The average length of E. cloacae bacteria in the stationary phase is about 2.3 +/- 0.6 microm, while under the stimulation of 400 mg/L CrO42-, the length of bacteria increases to 3.2 +/- 0.7 microm. Height and phase images showed that, with the addition of CrO42-, the smooth surface of bacteria changed into one with discontinuous features with characteristic dimension of 40-200 nm. Analysis reveals that these compact convex patches are organic components stimulated by CrO42-. A chromate resistance mechanism relating to the overexpression of extracellular biologic components for preventing the permeability of CrO42- into the cell is proposed as the survival strategy of E. cloacae in chromate situation.     

Degradation of Alkylphenols by White Rot Fungus Irpex lacteus and Its Manganese Peroxidase

Alkylphenols are common endocrine disrupters that are produced from the degradation of widely used surfactants. Since they cause various harmful effects on aquatic life and in humans, they should be removed from the environments being contaminated. White rot fungus Irpex lacteus can completely degrade 100?mg/L of octylphenol, nonylphenol, and phenylphenol during 1?day of incubation in the complex YMG medium, which was the highest degrading capability among nine strains of white rot fungi tested. In the N-limited Kirk??s basal salts medium, I. lacteus could degrade almost 100?% of 100?mg/L octylphenol and nonylphenol in 1?h, and exhibited a high activity of manganese peroxidase (MnP; 1,790?U/L). MnP of I. lacteus was purified by ion exchange chromatography, and this degraded 99?% of 50?mg/L octylphenol and removed 80?% of estrogenic activity in 2?hours. In addition, the purified MnP (10?U/mL) degraded over 90?% of 50?mg/L nonylphenol in 1?h.     

Speciation Determination of Chromium(VI) and Chromium(III) in Soil Samples after Cloud Point Extraction

Abstract

To measure the different activity of chromium(VI) and chromium(III) in soil samples, chromium(VI) and total chromium (CrVI + CrIII) was extracted by KCl extracting agent and alkali fusion, respectively. Cloud point extraction (CPE) for speciation determination of chromium with double-slotted quartz tube atom trap–flame atomic absorption spectrometry (STAT-FAAS) was developed. Preconcentration of chromium(VI) and total chromium in different pH solutions was achieved by CPE, with ammonium pyrrolidine dithiocarbamate (APDC) as the chelating agent and Triton X-114 as the cloud point extractant. The conditions of CPE and determination were studied. Under the optimal conditions, the enrichment factor was 50 for chromium from the initial 100-mL sample solution to the final 2-mL determined solution. Compared to the FAAS method, the sensitivity was improved seven-fold for chromium by the STAT-FAAS method. The limit of detection was 0.082 µg/L for chromium.     

Differential growth of the fungus Absidia cylindrospora on 13C/15N-labelled media

Many studies utilise enrichment of stable isotopes as tracers to follow the interactions occurring within soil food webs and methods have been developed to enrich bacteria, soil fauna and plant litter, Here for the first time we attempt to enrich a soil fungus to 99 atom% with (13)C and (15)N stable isotopes. In this study our objectives were to (a) assess whether the saprotrophic zygomycete fungus Absidia cylindrospora could grow on a medium enriched to 99 atom% with (13)C-glucose and (15)N-ammonium chloride, (b) to determine the level of enrichment obtained, and (c) to examine the change in growth rate of this fungus while it was growing on the dually enriched medium. To achieve this, the fungus was grown on agar enriched with (13)C and (15)N to 99 atom% and its growth rate monitored. The results showed that A. cylindrospora would grow on the highly labelled growth medium, but that its rate of growth was affected compared with the rate on either natural abundance media or media highly enriched with a single isotope ((13)C or (15)N). The implications of these results is that although the fungus is able to utilise these heavier isotopes, the biochemical processes involved in growth are affected, and consideration should be given to these differences when using stable isotope tracers in, for example, soil food web studies.     

三种植物对铀耐性及土壤中铀吸收积累差异的研究

采用溶液培养结合土壤培养的方法,研究了小白菜、冬苋菜和菠菜对铀的耐性及土壤中铀吸收积累的差异.结果表明:水培条件下(U 50mg/L),与小白菜和冬苋菜相比,菠菜对铀具有较强的耐性;在100mg/kg 土U的条件下,菠菜表现出比小白菜和冬苋菜更高吸收和积累铀的能力,其地上部分铀含量为232mg/kg DW(Dry Weight 干重),而根部铀含量达433mh/kg DW(Dry Weight 干重).菠菜可能对铀污染土壤的植物修复具有潜在的应用价值.     

Bioremediation of soil contaminated with organic compounds with special reference to acrylonitrile

Enrichment of acrylonitrile (AN) degrading bacterial culture from contaminated soil resulted in the isolation of two cultures which were identified as gram negative small rods (C1) and gram positive cocci (C2). One of the cultures (C1) was identified as Citrobacter fruendii on the basis of biochemical and physiological tests. Both the cultures (C1 and C2) were able to utilize acrylonitrile up to a concentration of 2000 mg/l as the sole source of carbon and nitrogen. The studies also confirmed that the acrylonitrile contaminated soil when ploughed with well mixed AN degrading culture, diammonium phosphate and farmyard manure, could be completely remediated within two months from the date of soil amendment.     

碱消解-火焰原子吸收光谱法测定土壤中六价铬

建立了碱消解-火焰原子吸收光谱法测定土壤中六价铬的方法.讨论了pH值对六价铬测定的影响.干扰实验的结果表明同等含量的三价铬对六价铬测定无干扰.实验对比了无背景校正、氘灯背景校正、塞曼背景校正三种工作方式,分别对低、中、高三个水平土壤六价铬标准物质进行了测定,结果表明,低含量的土壤样品用塞曼背景校正方式测定的结果更准确,...     

Intrinsic Characteristics of Cr6+-Resistant Bacteria Isolated from an Electroplating Industry Polluted Soils for Plant Growth-Promoting Activities

The Cr⁶⁺-resistant plant growth-promoting bacteria was isolated from soil samples that were collected from an electroplating industry at Coimbatore, India, that had tolerated chromium concentrations up to 500?mg Cr⁶⁺/L in Luria-Bertani medium. Based on morphology, physiology, and biochemical characteristics, the strain was identified as Bacillus sp. following the Bergey's manual of determinative bacteriology. Evaluation of plant growth-promoting parameters has revealed the intrinsic ability of the strain for the production of indole-3-acetic acid (IAA), siderophore, and solubilization of insoluble phosphate. Bacillus sp. have utilized tryptophan as a precursor for their growth and produced IAA (122???g/mL). Bacillus sp. also exhibited the production of siderophore that was tested qualitatively using Chrome Azurol S (CAS) assay solution and utilized the insoluble tricalcium phosphate as the sole source of phosphate exhibiting higher rate of phosphate solubilization after 72?h of incubation (1.45???g/mL). Extent of Cr⁶⁺ uptake and accumulation of Cr⁶⁺ in the cell wall of Bacillus sp. was investigated using atomic absorption spectrophotometer and scanning electron microscope-energy dispersive spectroscopy, respectively. The congenital capability of this Cr⁶⁺-resistant plant growth-promoting Bacillus sp. could be employed as bacterial inoculum for the improvement of phytoremediation in heavy metal contaminated soils.     

Kinetic studies of chromium (VI) binding to carboxylic acid- and methyl ester-functionalized silica/water interfaces important in geochemistry

Real-time kinetic measurements of hexavalent chromium binding to fused silica surfaces functionalized with carboxylic acid and methyl ester terminal groups are performed in situ using resonantly enhanced surface second harmonic generation (SHG) at pH 7 and 300 K. These functional groups were chosen because of their high abundance in humic acids and related biopolymers. Kinetic measurements are conducted in the submonolayer regime using chromate solution concentrations ranging from 1 x 10(-6) to 2 x 10(-5) M. The adsorption rates were analyzed using the standard Langmuir model and the Frumkin-Fowler-Guggenheim model. The desorption kinetics are consistent with a first-order process. These results indicate that hexavalent chromium mobility in carboxylic acid- and ester-rich soil environments increases with decreasing chromate concentrations. Based on the measured half-lives of the adsorbed Cr(VI) species, remobilization of bound hexavalent chromium due to natural or anthropogenic events that lower the chromate concentration in the aqueous phase can occur within minutes.     

Anion-exchange high-performance liquid chromatographic determination of ascorbic acid and hexavalent chromium in rat lung preparations after treatment with sodium chromate in vitro and in vivo

Simultaneous analysis of ascorbic acid and chromium (VI) in soluble fractions and bronchoalveolar lavage fluids of rat lungs treated with sodium chromate in vitro and in vivo was performed by anion-exchange high-performance liquid chromatography coupled to a photodiode-array detector. Absorbances at 265 and 370 nm were used for the determination of ascorbic acid and chromium (VI), respectively. The calibration graphs of standard solutions were linear in the test ranges of ascorbic acid an chromium (VI) (below 10 and 8 ppm, respectively). The detection limits of ascorbic acid and chromium (VI) were 1 and 0.5 ng, respectively. The recovery of ascorbic acid from lung tissues homogenized at pH 7.4 was 99%, and that of chromium (VI) was 96%, when tissues were homogenized under alkaline conditions (pH 11.4). Using this method, ascorbic acid levels in the soluble fractions and lavage fluids of normal rat lungs were determined. In the lung of a rat intratracheally injected with a saline solution of sodium chromate, ascorbic acid decreased to 80% of the normal level, and ca. 90% of the chromium (VI) was reduced within 4 min after injection, indicating that the ascorbic acid-related reduction of chromium (VI) is very rapid. The present method will be useful for studies of the reduction of chromium (VI) by ascorbic acid in biological systems.     

Sustainable Chromium (VI) Removal from Contaminated Groundwater Using Nano-Magnetite-Modified Biochar via Rapid Microwave Synthesis

This study developed a nano-magnetite-modified biochar material (m-biochar) using a simple and rapid in situ synthesis method via microwave treatment, and systematically investigated the removal capability and mechanism of chromium (VI) by this m-biochar from contaminated groundwater. The m-biochar was fabricated from reed residues and magnetically modified by nano-Fe₃O₄. The results from scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterisations confirmed the successful doping of nano-Fe₃O₄ on the biochar with an improved porous structure. The synthesised m-biochar exhibited significantly higher maximum adsorption capacity of 9.92 mg/g compared with that (8.03 mg/g) of the pristine biochar. The adsorption kinetics followed the pseudo-second-order model and the intraparticle diffusion model, which indicated that the overall adsorption rate of Cr(VI) was governed by the processes of chemical adsorption, liquid film diffusion and intramolecular diffusion. The increasing of the pH from 3 to 11 significantly affected the Cr(VI) adsorption, where the capabilities decreased from 9.92 mg/g to 0.435 mg/g and 8.03 mg/g to 0.095 mg/g for the m-biochar and pristine biochar, respectively. Moreover, the adsorption mechanisms of Cr(VI) by m-biochar were evaluated and confirmed to include the pathways of electrostatic adsorption, reduction and complexation. This study highlighted an effective synthesis method to prepare a superior Cr(VI) adsorbent, which could contribute to the effective remediation of heavy metal contaminations in the groundwater.     

Assessment of Metal Contamination in Shallow Coastal Sediments Around Mytilene Greece

Abstract

Different normalisation procedures were applied on a data set of metal concentrations of sediments from 28 stations in the harbour and coastal area of Mytilene, Lesvos island, Greece. Due to the great granulometric variability of the sediments the normalisation for grain-size was not applicable. Also, the normalisation to a carbonate-free basis did not provide additional information. On the other hand the normalisation to Al and the calculation of enrichment factors of metals enabled to distinguish between contaminated and non-contaminated areas. The harbour sediments were highly enriched in Cd, Cu and Zn and also slightly enriched in Pb. No enrichment was found in the sediments of the coastal area outside the harbour, indicating that the metal rich deposits of that confined area are not affecting the quality of the neighbouring coastal environment.     

Spezifische Reaktion zum Nachweis von Chrom(III) und Chromat

Zusammenfassung Ein Tüpfelnachweis für Chrom(III) und Chromat wurde angegeben. Nach Reduktion mit metallischem Zink bildet Chrom(II) mit Phenoxazinfarbstoffen in salzsaurem Milieu violett gefärbte Lösungen. Die Reaktion ist für Chrom spezifisch. IhrpD-Wert beträgt 5,3.

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Specific reaction for the detection of chromium(III) and chromate

Summary A spot test detection of chromium(III) and chromate is given. After reduction with metallic zinc, the resulting chromium(II) yields violet solutions with phenoxazine dyestuffs in a hydrochloric acid medium. The reaction is specific for chromium. ItspD is 5.3.

     

X-ray fluorescence spectrometric determination of sulfur-containing anionic surfactants in water after their enrichment on a membrane filter as an ion-pair complex with a cationic surfactant.

Anionic surfactants containing sulfur in their structure were enriched on a mixed cellulose ester membrane filter (MF) by filtration as an ion-pair complex with a cationic surfactant. After their enrichment, the anionic surfactants were determined by X-ray fluorescence spectrometry of the sulfur enriched on the MF. A linear calibration was obtained over a concentration range from 0.05 to 0.8 mg L(-1) of sodium dodecyl sulfate as a standard material with less than 6% RSD. The detection limit based on 3s for the reagent blank was 2 microg L(-1). This method is very simple, rapid and highly selective for sulfur-containing surfactants, and does not require any organic solvent extraction. This method was applied to the determination of anionic surfactant in some urban river waters where domestic wastewater was discharged. The results were compared with those obtained by conventional solvent extraction-spectrophotometry. The distribution of the analyte complexes within the MF where the ion-pair was retained is also discussed.     

Intracellularly grown gold nanoislands as SERS substrates for monitoring chromate,sulfate and nitrate localization sites in remediating bacteria biofilms by Raman chemical imaging

Understanding the chemical composition of biofilm matrices is vital in different fields of biology such as surgery, dental medicine, synthetic grafts and bioremediation. The knowledge of biofilm development, composition, active reduction sites and remediation efficacy will help in the development of effective solutions and evaluation of remediating approaches prior to implementation. Surface-enhanced Raman spectroscopy (SERS) based imaging is an invaluable tool to obtain an understanding of the remediating efficacy of microorganisms and its role in the formation of organic and inorganic compounds in biofilms. We demonstrate for the first time, the presence of chromate, sulfate, nitrate and reduced trivalent chromium in soil biofilms. In addition, we demonstrate that SERS imaging was able to validate two observations made by previous studies on chromate/sulfate and chromate/nitrate interactions in Shewanella oneidensis MR-1 biofilms. Additionally, we show a detailed Raman mapping based evidence of the existence of chromate–sulfate competition for cellular entry. Subsequently, we use Raman mapping to study the effect of nitrate on chromate reduction. The findings presented in this paper are among the first to report – detection of multiple metallic ions in bacterial biofilms using intracellular SERS substrates. Such a detailed characterization of biofilms using gold nanoislands based SERS mapping substrate can be extended to study cellular localization of other metallic ions and chemical species of biological and toxicological significance and their effect on reduction reactions in bacterial biofilms.