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Molecular Advances in Bioremediation of Hexavalent Chromium from Soil and Wastewater
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
Aditi Nag, Devendra Sharma, Sudipti Arora
The element chromium (Cr) is a heavy metal. It has an atomic number of 24. It is present as the first element in group number six and as the fourth transition metal on the periodic table. Cr is reported as the 17th most abundant element present in the Earth’s mantle, the most abundantly available heavy metal in the lithosphere, along with zinc, and stands 21st on the list of most abundant elements in the Earth’s crust ranging from 100–300 µg/g (Cervants et al., 2001). Thus, overall it is reported that Cr is the seventh most abundant element on Earth (Mohanty and Kumar Patra, 2013). Cr occurs naturally in rocks, soil, plants, animals, volcanic dust, and gases, among others It can be found as chromite (FeCr2O4) or as a complex with other metals like crocoite (PbCrO4), bentorite (Ca6[Cr,Al]2[SO4]3), tarapacaite (K2CrO4), and vauquelinite (CuPb2CrO4PO4OH). Cr is widely used in the textile, leather, and metal industries for making textile dyes and mordants, pigments, tanning of animal hides as plating, as an alloying agent, in the inhibition of water corrosion, in ceramic glazes and refractory bricks, etc. This wide range of applications has led to a high anthropogenic use of Cr, which has consequently led to environmental contamination. Thus, Cr presence in the environment has become an increasing concern in the last few years (Oliveira, 2012).
Toxic and carcinogenic effects of hexavalent chromium in mammalian cells in vivo and in vitro: a recent update
Published in Journal of Environmental Science and Health, Part C, 2022
Shehnaz Islam, Sreejata Kamila, Ansuman Chattopadhyay
Chromium (Cr) is the 21st most abundant element in the Earth’s mantle.1 It is a naturally occurring trace element present as chromite (FeCr2O4) in ultramafic and serpentine rocks or complexed with other metals like crocoite (PbCrO4), bentorite Ca6Cr2(SO4)3(OH)12 · 26H2O, tarapacaite (K2CrO4), and vauquelinite (CuPb2(CrO4)(PO4)(OH)), among others.2 This transition metal has seven oxidation states and the elemental [Cr (0)], trivalent [Cr (III)] and hexavalent [Cr (VI)] states are the most prevalent forms.3,4 Studies have shown that organic-Cr (III) species can be transformed into chromium (III) hydroxide [Cr (OH)3] nanocrystal with time. Chromium (III) oxide [Cr2O3] is transformed from Cr(OH)3 nanocrystals via dehydration, which is a more stable compound and helps in the mineralization and immobilization process of Cr.5 Environmental contamination of Cr (VI) occurs due to anthropogenic uses of various chromate compounds in industrial sectors like stainless steel and alloy production, welding, chrome electroplating, tanning of animal hides, textile pigments and dyes, reduction of water corrosion, ceramic glazes, refractory bricks etc. Anthropogenic sources contribute to almost 35% of all the Cr (VI) compounds.6 The widespread industrial applications have led to the rapid environmental accumulation of this metal to become a global public health concern in recent years (Table 1).7