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Remediation of Metal Pollutants in the Environment
Published in Maulin P. Shah, Sweta Parimita Bera, Günay Yıldız Töre, Advanced Oxidation Processes for Wastewater Treatment, 2022
Ambreen Ashar, Nida Naeem, Noshin Afshan, Mohammad Mohsin, Zeeshan Ahmad Bhutta
Two basic forms of hexavalent chromium are chromate and dichromate ions. The hexavalent state is movable in water and soil and is its most toxic form and also considered as carcinogenic substance for human health while the trivalent state is believed as a micro-nutrient for human, compulsory element for lipid and sugar metabolism (H. Oliveira, 2012). The hexavalent state is hazardous and mutagen while Cr(III) is an important nutrient in small quantities. Cr(VI) can be agglomerated biologically in the food chain and thus poses a serious hazard to human health (Cervantes et al., 2001; Costa, 1997; Igiri et al., 2018).
Practical Applications: Metals Contamination
Published in William J. Deutsch, Groundwater Geochemistry, 2020
At trace concentrations chromium appears to be an important nutrient in the human diet; however, as with other trace elements, it is also toxic at above average concentrations. In cases of very high exposure Cr can be toxic and carcinogenic.8 Cr(VI) is usually identified as the toxic form of chromium because it occurs as the fairly mobile anion Chromate (CrO42−), and its minerals are soluble in the natural environment. Relatively high concentrations of Cr(VI) are possible in the environment compared with Cr(HI), which forms an insoluble hydroxide mineral, Cr(OH)3. Many industries use the Chromate and dichromate (Cr2O72−) forms of chromium for such applications as corrosion inhibition because of the strong oxidizing ability of these species. It has been reported that the dust emitted from ferrochrome smelters contains on the order of 40% chromium as Cr(VI), whereas chromium in sewage sludge is predominantly in the Cr(III) valence state because of the reducing environment.8
Inorganic Chemicals in Drinking Water
Published in Joseph Cotruvo, Drinking Water Quality and Contaminants Guidebook, 2019
Chromium is a transition element, the 21st most abundant element in the earth’s crust and widely distributed. It is found in plants, rocks, foods, and animals in small amounts. The two most common forms are Cr(III) and Cr(VI). Chromium VI is a component of chromium stainless steel; Cr(VI) on the steel surface prevents rust formation. Chromium is generally present in the environment from the natural geology in both forms, and also from industrial discharges in some locations. The chromate and dichromate salts are used as pigments and colorants in glazes, paints and in pyrotechnic displays, giving characteristic yellow colors.
A critical review on bioremediation technologies for Cr(VI)-contaminated soils and wastewater
Published in Critical Reviews in Environmental Science and Technology, 2019
Shaopan Xia, Zhaoliang Song, Paramsothy Jeyakumar, Sabry M. Shaheen, Jörg Rinklebe, Yong Sik Ok, Nanthi Bolan, Hailong Wang
Chromium (Cr) is categorized as the No.1 carcinogenic substance (Zhitkovich, 2011) and it is ranked No.5 among the potentially toxic elements (PTEs) according to the Comprehensive Environmental Response, Compensation, and Liability Act (Ma, Hung, & Chen, 2007). It is also one of the top 20 toxic substances in superfund controlled contaminated sites in the United States (Chrysochoou, Johnston, & Dahal, 2012). Chromium usually exists in the stable Cr(III) and Cr(VI) valence states. Trivalent chromium compounds are sorbed by soil colloids to form precipitates with extremely low solubility, which hinders its leaching into groundwater or its absorption by plants. By contrast, Cr(VI) species including chromate and dichromate compounds (CrO42−, HCrO4− and Cr2O72−) exhibit strong oxidation and high solubility (Reale et al., 2016; Ashraf et al., 2017). Hence, Cr(VI) is very active in soil and wastewater, and it has the potential to be hidden and persist in the long-term because of its non-biodegradability (Shekhawat, Chatterjee, & Joshi, 2015; Antoniadis et al., 2018; Jobby, Jha, Yadav, & Desai, 2018). Chromium pollution presents a high ecological risk and it can harm the health of living organisms. A typical example of Cr(VI) pollution in drinking water led to the appearance of “cancer villages” in some regions of Liaoning Province, China (Beaumont et al., 2008).
Ultrasonic green synthesis of different nickel nanoparticles and their application in Cr(VI) removal studies
Published in Inorganic and Nano-Metal Chemistry, 2021
Maria Zaib, Misbah Jamil, Tayyaba Shahzadi, Umar Farooq
With non-regulated industrialization, discharge of heavy metals in waters bodies has enormously increased and thus significantly disturbs the geochemical cycling. and Biomagnification of heavy metals in food chain process is also becoming common.[5] Cr (III) and Cr (VI) are most abundant oxidation states of chromium.[6] The hexavalent (VI) and trivalent (III) forms of chromium are inter-convertible.[7,8] Cr (III) produces mononuclear, neutral and poly nuclear species in natural aqueous systems. Concentrations of chromium (III) oxides are finite in natural water due to less water-soluble nature.[9,10] Chromium (VI) compounds are considered very toxic to flora and fauna and found to be more virulent than chromium (III).[11,12] On hydrolysis, Cr (VI) produce only neutral and anionic species. Chromate and dichromate are the most toxic and highly water-soluble forms of hexavalent chromium. Chromium and its salts are employed in different industries of tanning, painting, dying, electroplating and mining.[13] Due to lack of effective removal methodologies, concentration of Cr (VI) in industrial wastewater ranges from 0.5 to 270 mg/L. This concentration range proved to be mutagenic and leads to deteriorated health conditions of nausea, internal hemorrhage, dermatitis, respiratory problems and asthma. There is an utmost need that prior to discharge, effluent containing Cr (VI) should be properly treated.[14,15]