Phytoremediation of toxic heavy metals by Brassica plants: A biochemical and physiological approach

Abstract

Contamination of soils and water bodies by toxic heavy metals (HMs) such as cadmium (Cd), chromium (Cr), mercury (Hg), arsenic (As), lead (Pb), and zinc (Zn), is a major environmental concern. Phytoremediation by botanical genus Brassica emerges as an important technique, in which plants are used to decontaminate these areas. Brassica spp. are reported as potential phytoremediators and hyperaccumulators our aim was to elucidate the physiological and biochemical potential use of different species belonging to the genus Brassica to bioremediate and tolerate the harmful effects of these environmental contaminants on their metabolism. Since these species display efficient phytoremediation processes, such as phytovolatilization, phytostabilization, and phytoextraction. These species also have physiological processes that aid the absorption, translocation, and accumulation of toxic HMs into low-activity cell organelles, in addition to an efficient enzymatic and non-enzymatic defense mechanism that attenuates the oxidative damage induced by the overproduction of reactive oxygen species (ROS). In addition to enzymatic and non-enzymatic mechanisms, our review also is an effort to gather the scattered information on other phytoremediation assistive techniques, such as the use of chelating and acidifying agents, selection of tolerant cultivars, and genetic engineering. Although techniques for the management and disposal of biomass obtained after the phytoremediation process are reported, this issue still lacks studies that present a consensus regarding which techniques are safer, more efficient, and economically viable. Phytoremediation of toxic HMs by Brassica species is, a promising technique, however, the need for further studies aimed at agronomic techniques that assist in high plant biomass production, tolerance and, structuring the hyperaccumulation network of these contaminants, so that their applicability and feasibility can be used for larger areas (cropping areas).