Bioremediation strategies for chromium removal: Current research, scale-up approach and future perspectives

The reduction of Cr(VI) to Cr(III) mediated by environmentally relevant carboxylic acids: State-of-the-art and perspectives.

Leaching behavior of metals from iron tailings under varying pH and low-molecular-weight organic acids

Dramatically enhanced aerobic Cr(VI) reduction with scrap zero-valent aluminum induced by oxalate

Chromium (Cr) is a highly toxic metal for microorganisms as well as plants and animal cells. Due to its widespread industrial use, Cr has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The study of the interactions between microorganisms and Cr has been helpful to unravel the mechanisms allowing organisms to survive in the presence of high concentrations of Cr(VI) and to detoxify and remove the oxyanion. Various mechanisms of interactions with Cr have been identified in diverse species of bacteria and fungi, including biosorption, bioaccumulation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution using bioreactors or by in situ treatments. In this review, the interactions of microorganisms with Cr are summarised, emphasising the importance of new research avenues using advanced methodologies, including proteomic, transcriptomic, and metabolomic analyses, as well as the use of techniques based on X-ray absorption spectroscopy and electron paramagnetic resonance spectroscopy.

Microbial interactions with chromium: basic biological processes and applications in environmental biotechnology

Mechanistic insight into chromium(VI) reduction by oxalic acid in the presence of manganese(II).

Rationale Quantification of small molecules by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) is challenging yet attractive, due to micro-scale procedural simplicity, high throughput and lack of memory effects. Since these features are important while analyzing trace elements in quality control schemes, MALDI-TOFMS was used for the determination of copper (Cu) and lead (Pb) in tequila with quantification carried out by partial least squares regression (PLS2) and by univariate calibration (UC). Methods In the proposed procedure, Bi(III) was added as internal standard (IS), diethyldithiocarbamate complexes were formed (pH 7.4) and extracted into chloroform; after solvent evaporation and re-constitution in acetonitrile, the sample was co-crystallized with α-cyano-4-hydroxycinnamic acid on a steel target. From the acquired mass spectra, UC was performed using IS-normalized signals of the monoisotopic ions of analytes, and the m/z range 350-513 was used for PLS2. Accuracy was tested by recovery experiments and by inductively coupled plasma (ICP)-MS analysis. Results When compared with direct analyte signal measurements, application of IS yielded enhanced analytical performance using either UC or PLS2; the method quantification limits were: 11.1 μg L-1 , 23.4 μg L-1 for Cu and 89.8 μg L-1 , 97.1 μg L-1 for Pb, respectively. In tequila, MALDI-TOFMS and ICP-MS provided consistent results for Cu (165-2599 μg L-1 ); Pb was not detected in any sample by MALDI-TOFMS, yet recoveries obtained after standard addition were indicative of acceptable accuracy (400 μg L-1 Pb added; recoveries: 91.2-108% for UC and 98.8-120% for PLS2). Conclusions New experimental evidence has been provided supporting the inclusion of trace metals quantification within a range of MALDI-TOFMS applications. Slightly better results were obtained for UC as compared with PLS2 yet both methods can be recommended for testing the compliance of Cu and Pb levels with Official Mexican Norm. Of note, while using PLS2, there is no need for signal integration nor for IS normalization.

Determination of copper and lead in tequila by conventional matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and partial least squares regression

In this work, a procedure for the determination of mercury and copper in canned tuna samples is presented, based on the extraction of their respective dithizone complexes and quantification by conventional MALDI-TOFMS with the aid of partial least square regression (PLS2). Methanolic dithizone solution (1 ml, 0.01% m/v) containing Ag(I) as internal standard was added to the calibration solutions and to the acid-digested samples (5 ml, pH 3); copper, mercury, and silver complexes were extracted to cyclohexane (1.5 ml), and after evaporation, the residues were re-constituted in acetone (100 μl). The samples were prepared by dried droplet crystallization with α-cyano-4-hydroxycinnamic acid. The experimental and MALDI-TOFMS instrument operating conditions were set up under criteria of as high as possible detectability and repeatability. When univariate calibration was carried out using the most intense ion of Cu or Hg complex normalized by internal standard, determination seemed feasible yet precision of the results was poor. Taking baseline-corrected spectra in m/z range 560–725, PLS2 model was constructed for the prediction of two elements with the method quantification limits 63 μg kg−1 for Cu and 75 μg kg−1 for Hg, respectively. For different brands of canned tuna, the results obtained by MALDI-TOFMS combined with PLS2 and by ICP-MS were in good agreement. The proposed procedure is an attractive alternative for the determination of trace metals in foods because of the procedural simplicity, micro-scale dimension, high speed of data acquisition/processing, and the cost of instrument operation lower as compared to any atomic spectrometry technique.

Application of MALDI-TOFMS Combined with Partial Least Square Regression for the Determination of Mercury and Copper in Canned Tuna, Using Dithizone as the Complexing Agent and Ag(I) as Internal Standard

Manuel Mendez Garcia

Papers

Mechanistic insight into chromium(VI) reduction by oxalic acid in the presence of manganese(II).

Determination of copper and lead in tequila by conventional matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and partial least squares regression

Application of MALDI-TOFMS Combined with Partial Least Square Regression for the Determination of Mercury and Copper in Canned Tuna, Using Dithizone as the Complexing Agent and Ag(I) as Internal Standard