The Chemistry and Toxicity of Chromium Pollution: An Overview

As a heavy metal, chromium (Cr) has significant importance in the current industrial scenario, however, it poses an environmental threat as well. Generally, there are two stable forms of Cr available in environmental matrices, the relatively less toxic trivalent Cr(III) and the highly toxic hexavalent Cr(VI). Industrial sites release hazardous Cr(VI) with effluents during the post-production stage, causing water and soil pollution worldwide. Cr(VI) is one of the priority pollutants as per USEPA (United States Environmental Protection Agency) classification and it is one of the well-known carcinogens. In most cases, it is released from anthropogenic activities like mining, steel making, welding, tanning, textile dyeing, wood polishing, etc. Whenever Cr(VI) contamination exceeds the threshold limits, it has a deleterious impact on public health and the vegetation of the site contaminated. In the present investigation, the major focus is on the anthropogenic sources of Cr(VI) release into water bodies and soil, its adverse effects, as well as remediation of these emerging environmental problems. The present review focuses on the removal of Cr from environmental media by conventional biological methods. Many advanced technologies have been developed and applied recently to remove Cr from contaminated soils and water, including membrane technology, electrocoagulation, ion exchange, and electrodialysis. In addition, alternative techniques like phytoremediation processes were established which offer an environmentally sustainable, eco-friendly, and cost-effective approach to removing Cr. With an emphasis on the cleanup of soils and water systems contaminated by Cr, this review summarizes the bioavailability of Cr, the uptake pathways, the accumulation process, and the current status of phytoremediation research. A recent finding about Cr localization in hyperaccumulator plant species is also described in this paper. This review describes the process of plant metabolism changes in response to Cr stress and the mechanisms that allow plants to remove Cr through the phytoremediation process.