Microbial Reduction of Hexavalent Chromium as a Mechanism of Detoxification and Possible Bioremediation Applications

Abstract

that Cr III is involved in the tertiary structure of proteins and in the conformation of cell RNA and DNA [ , ]. . . Toxicity of chromiumCr VI exposure in humans can induce allergies, irritations, eczema, ulceration, nasal and skin irritations, perforation of eardrum, respiratory track disorders and lung carcinoma [ , , ]. Moreover, Cr VI evidences the capability to accumulate in the placenta, damaging fetal development [ ]. Cr VI pollution in the environment alters the structure of soil microbial communities [ ], reducing microbial growth and related enzymatic activities, with a consequent persistence of organic matter in soils and accumulation of Cr VI [ ].The toxic action of Cr VI is due to its capability to easily penetrate cellular membranes, and cell membrane damages caused by oxidative stress induced by Cr VI have been extensively reported, both in eukaryotic and prokaryotic cells, with effects such as loss of membrane integrity or inhibition of the electron transport chain [ , ]. Moreover, Cr VI enters cells using the sulfate transport system of the membrane in cells of organisms that are able to use sulfate [ , , , , , ].Once Cr VI entered into cells, spontaneous reactions occur with the intracellular reductants as ascorbate and glutathione, generating the short-lived intermediates Cr V and/or Cr IV , free radicals and the end-product Cr III [ , , ]. In the cytoplasm, Cr V is oxidized to Cr VI and the process produces a reactive oxygen species, referred as ROS, that easily combines with DNA-protein complexes. On the other hand, Cr IV is able to bind to cellular materials, altering their normal physiological functions [ , ]. It is known that Cr VI species and hydroxyl radicals cause DNA lesions in vivo [ ]. The intermediates that originated from the action of Cr VI are dangerous to cell organelles, proteins and nucleic acids [ , , ]. Cr VI is a very dangerous chemical form on biological systems as it can induce mutagenic, carcinogenic and teratogenic effects. Moreover, Cr VI is able to induce oxidative stress in cells, damaging its DNA [ ]. Inside of cells, the Cr III -DNA adducts and related hydroxyl radical oxidative DNA damages have a central role in originating the genotoxic and mutagenic effects [ ]. Moreover, the formation of Cr III -DNA binary adducts and L-cysteine-Cr III -DNA and ascorbateCr III -DNA ternary adducts likely increase both genotoxicity and mutagenicity in human cells [ , ]. Again the formation of DNA protein cross-linking, a process favoured by Cr VI , induces a significant promutagenic effect [ ].Considering the dangerous effects Cr VI can cause to human health, Cr VI has been comprised among priority pollutants and listed as a class A human carcinogen by the US Environmental Protection Agency USEPA [ ].The cell membrane is nearly impermeable to Cr III , Cr III has thus only about one thousandth of the toxicity of Cr VI [ , ]. Taking into account these considerations, it is possible to conclude that, depending on its oxidation state, chromium can have different biological effects,...

Enhancement of Chromium (VI) Reduction in Microcosms Amended with Lactate or Yeast Extract: A Laboratory-Scale Study

“…A total number of 60 reactors were prepared in previously sterilized 250 mL PE bottles for investigating the four experimental conditions in triplicate, at five times of incubation (4,7,11,14, and 28 days), which correspond to T1, T2, T3, T4, and T5 investigation times, respectively.…”

“…The toxic action of Cr(VI) is due to its ability to easily penetrate cellular membranes. Cell membrane damages caused by oxidative stress induced by Cr(VI) have also been extensively reported, both in eukaryotic and prokaryotic cells [2][3][4].…”

Microbial Assisted Hexavalent Chromium Removal in Bioelectrochemical Systems

“…In addition to endogenous electron reserves, the electrode posed at −0.3 V can act as a further electron source [46], that could have promoted chromium reduction. Additional biological mechanisms of chromium reduction, such as enzyme reduction (soluble or membrane-associated reductase) [21], intracellular detoxification mechanisms [45,47] and adsorption on the cell surface [48,49] may have occurred equally in both biological systems.…”

Photocatalytic Degradation of Salicylic Acid and Reduction of Cr(VI) using TiO2

“…In aquatic environments, chromium exists mostly in the hexavalent chromium Cr(VI) and trivalent chromium Cr(III) states. Anionic Cr(VI) is far more mobile and toxic than Cr(III) and more difficult to remove from water [7]- [8]. Similar to many other metal cations, however, aqueous Cr(III) can be readily precipitated as Cr(OH) 3 or removed by adsorption and ion exchange.…”