Effect of Hexavalent Chromium [Cr(VI)] on Phytoremediation Potential and Biochemical Response of Hybrid Napier Grass with and without EDTA Application

Are Grasses Really Useful for the Phytoremediation of Potentially Toxic Trace Elements? A Review

The pollution of soil, water, and air by potentially toxic trace elements poses risks to environmental and human health. For this reason, many chemical, physical, and biological processes of remediation have been developed to reduce the (available) trace element concentrations in the environment. Among those technologies, phytoremediation is an environmentally friendly in situ and cost-effective approach to remediate sites with low-to-moderate pollution with trace elements. However, not all species have the potential to be used for phytoremediation of trace element-polluted sites due to their morpho-physiological characteristics and low tolerance to toxicity induced by the trace elements. Grasses are prospective candidates due to their high biomass yields, fast growth, adaptations to infertile soils, and successive shoot regrowth after harvest. A large number of studies evaluating the processes related to the uptake, transport, accumulation, and toxicity of trace elements in grasses assessed for phytoremediation have been conducted. The aim of this review is (i) to synthesize the available information on the mechanisms involved in uptake, transport, accumulation, toxicity, and tolerance to trace elements in grasses; (ii) to identify suitable grasses for trace element phytoextraction, phytostabilization, and phytofiltration; (iii) to describe the main strategies used to improve trace element phytoremediation efficiency by grasses; and (iv) to point out the advantages, disadvantages, and perspectives for the use of grasses for phytoremediation of trace element-polluted soils.

Chromium Stress in Plants: Toxicity, Tolerance and Phytoremediation

Extensive industrial activities resulted in an increase in chromium (Cr) contamination in the environment. The toxicity of Cr severely affects plant growth and development. Cr is also recognized as a human carcinogen that enters the human body via inhalation or by consuming Cr-contaminated food products. Taking consideration of Cr enrichment in the environment and its toxic effects, US Environmental Protection Agency and Agency for Toxic Substances and Disease Registry listed Cr as a priority pollutant. In nature, Cr exists in various valence states, including Cr(III) and Cr(VI). Cr(VI) is the most toxic and persistent form in soil. Plants uptake Cr through various transporters such as phosphate and sulfate transporters. Cr exerts its effect by generating reactive oxygen species (ROS) and hampering various metabolic and physiological pathways. Studies on genetic and transcriptional regulation of plants have shown the various detoxification genes get up-regulated and confer tolerance in plants under Cr stress. In recent years, the ability of the plant to withstand Cr toxicity by accumulating Cr inside the plant has been recognized as one of the promising bioremediation methods for the Cr contaminated region. This review summarized the Cr occurrence and toxicity in plants, role of detoxification genes in Cr stress response, and various plants utilized for phytoremediation in Cr-contaminated regions.

Successful Outcome of Phytostabilization in Cr(VI) Contaminated Soils Amended with Alkalizing Additives

This study analysed the effect of three alkalizing soil amendments (limestone, dolomite chalcedonite) on aided phytostabilization with Festuca rubra L. depending on the hexavalent chromium (Cr(VI)) level in contaminated soil. Four different levels of Cr(VI) were added to the soil (0, 50, 100 and 150 mg/kg). The Cr contents in the plant roots and above-ground parts and the soil (total and extracted Cr by 0.01 M CaCl2) were determined with flame atomic absorption spectrometry. The phytotoxicity of the soil was also determined. Soil amended with chalcedonite significantly increased F. rubra biomass. Chalcedonite and limestone favored a considerable accumulation of Cr in the roots. The application of dolomite and limestone to soil contaminated with Cr(VI) contributed to a significant increase in pH values and was found to be the most effective in reducing total Cr and CaCl2-extracted Cr contents from the soil. F. rubra in combination with a chalcedonite amendment appears to be a promising solution for phytostabilization of Cr(VI)-contaminated areas. The use of this model can contribute to reducing human exposure to Cr(VI) and its associated health risks.