In contrast with Cr(III), Cr(VI) enters cells via a non-specific anion carrier, the permease system, which transports a number of anions, such as SO 4 2− and PO 4 3− and is reduced to Cr(III) there via the unstable Cr(V) and Cr(IV). Biological membranes are impermeable for Cr(III) ions and Cr(III) has a high affinity to form complexes with most biologically relevant molecules. Cr(VI) most often exists in the forms of CrO 4 2− (chromate ion) and Cr 2O 7 2− (dichromate ion), especially in solution, these being most potent mutagenic, carcinogenic and toxic agents. Although various valency states of chromium are known, Cr(III) and Cr(VI) are prominent in nature. The Cr(VI)-sensitivity was due to a significantly increased uptake of Cr(VI).Ĭr(VI) uptake, Cr(VI)-sensitivity, Schizosaccharomyces pombe 1 IntroductionĮnvironmental exposure to the various forms of chromium remains a serious problem throughout the world. The wild-type strain exhibited a lower TOCr content than that of its mutants and only 35% of this was OBCr. Under these conditions, the sensitive and tolerant mutants had the same TOCr content, 50% of which was OBCr. In PIPES buffer, washed, lysine-starved biomasses were treated with 75 µM Cr(VI) and after 2 h, the TOCr and the organically bound chromium (OBCr) were determined. The sensitive mutant exhibited a high bioaccumulation ability, with a dry biomass of 810 µg g −1 after 30 min, while the tolerant mutant had a significantly lower ability than the wild-type strain. Cr(VI) was added to the actively growing cultures and the total chromium (TOCr) content of the cells was determined. The mutants exhibited cross-sensitivity of various patterns to Cd 2+, Cu 2+, Ni 2+, Zn 2+ and VO 4 3−. The minimal inhibitory concentrations of K 2Cr 2O 7 on YEA media were 225 µM for the wild-type strain CW-6, 125 µM for the sensitive mutant CS-6.51 and 275 µM for the tolerant mutant CT-6.66. Many other materials are also tested for Hexavalent Chromium.Lysine and leucine auxotrophic, heterothallic (h +, h −) strains of Schizosaccharomyces pombe were used to obtain chromium(VI)-sensitive and -tolerant mutants by ultraviolet radiation-induced and nitrosoguanidine-induced mutagenesis.Textile Dyes: Ammonium dichromate, Potassium chromate, Potassium dichromate, Sodium chromate.Stainless Steel: Hexavalent chromium Cr(VI) compounds.Coatings, Platings: Chromic trioxide (chromic acid), Zinc chromate, Barium chromate, Calcium chromate, Sodium chromate, Strontium chromate.
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