Abstract
Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. 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. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. 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. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.
Highlights
Chromium is a transition metal that exhibits a complex chemistry
Ingesting less than 2 g of Cr (VI) compound can result in kidney and liver damage after 1–4 days of exposure, while a dose of 2–5 g of a soluble hexavalent chromium compound can be fatal to an adult human [1]
The genotoxicity of chromium, once it is introduced into human cells, can manifest favouring genomic instability, cancer onset, cell cycle arrest, and apoptosis
Summary
Chromium is a transition metal that exhibits a complex chemistry. In water, chromium exists with oxidation states ranging from +6 to −2. Environmental 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 [11,12,13] 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 [14,15,16]. Traditional approaches for Cr (VI) removal from water and wastewaters include physico-chemical methods such as chemical reduction, adsorption on porous surfaces with sites for ion exchange, and electrocoagulation These strategies are highly efficient for a high content of Cr (VI), but some limitations are related to sludge production, large amount of chemicals required, and consequent risk of secondary pollution [20].
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