In addition, the fall out of ashes produced by the incineration of coal or municipal waste for energy generation and the production of second-generation fertilizers contribute to the elevated Cr (VI) content in soil and water. These include mining and metal works, steel and metal alloys production, paint manufacturing, wood and paper processing, dyeing, and raising the chromium content in wastewater. Įnvironmental contamination of Cr (VI) is gaining more consideration because it is widespread throughout the world with high levels in water and soil owing to natural and anthropogenic activities. On a cellular level, the genotoxic effect of chromium leads to oxidative stress, DNA damages, and other harms that can result in tumour development. A lasting and continuative exposure to chromium even at low concentration, that is, in the case of occupational exposure, can damage the skin, eyes, blood, respiratory, and immune system. The risks for human health are dependent on dose, exposure level, and duration. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Otherwise, Cr (VI) can be easily reduced to Cr (III) by different reducing agents including Fe (II), phosphate, sulphide, and organic matter, for example, humic acid. In nature, the oxidation of Cr (III) is not favoured because of the high E° value of the Cr (III)/Cr (VI) redox couple, only manganese oxide seems to be an effective oxidant in the environment. Depending on the solution pH values, chromium can be encountered mainly as Cr (III) or Cr (VI). The most stable forms are the hexavalent Cr (VI) and trivalent Cr (III) ones and can interconvert with each other. In water, chromium exists with oxidation states ranging from +6 to −2. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.Ĭhromium is a transition metal that exhibits a complex chemistry. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Once in water, chromium mainly occurs in two oxidation states Cr (III) and Cr (VI) and related ion forms depending on pH values, redox potential, and presence of natural reducing agents. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. Moreover, Cr (VI) pollution is largely related to several Cr (VI) industrial applications in the field of energy production, manufacturing of metals and chemicals, and subsequent waste and wastewater management. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources.
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