Pooja Mahajan, Shivam Singla and Jyotsna Kaushal
Brassica; heavy metals; Phytoremediation; Hyperaccumulator .
|PUBLISHED DATE||March 14, 2016|
|PUBLISHER||The Author(s) 2016. This article is published with open access at www.chitkara.edu.in/ publications|
Remediation of contaminated sites with toxic and heavy metals is particularly a challenging task. Therefore pre-treatment is needed before the discharge of these effluents. Among all method investigated presently, Phytoremediation is found to be an emerging and most innovative tool for removal of environmental contaminants such as heavy metals, trace elements, radioactive compounds and organic compounds from soil or water. It has been proposed as a cost-effective and environmental friendly technique. It involves the use of either naturally occurring metal hyper accumulator plants or genetically engineered plants. Indian mustard known as Brassica juncea is well known hyper accumulator. This paper aims to compile some information about sources of heavy metals and their toxicity. It also reviews deeply about phytoremediation technology, including the heavy metal uptake mechanisms and several case studies associated with Brassica juneca.
Humans and ecosystem may be exposed to heavy metals such as Pb, Cr, Cu, As, Cd, Ni, Hg, Zn, Cs etc. through the direct consumption of crops and vegetables grown on the contaminated soils or potable water. Enhanced level of heavy metals in soil poses a threat to human, animals. In world all over, awareness about degradation of environment and its impact on human and animals has raised the interest among the researchers in the development of technologies to remediate contaminated sites. In highly populated countries where there are less funds available for environmental restoration, there is a need for low-cost and ecologically sustainable technologies to remediate the lands which are contaminated with heavy metals so as to reduce the risks and make the resource available for agricultural production, enhance food security and for solving scale down land tenure problems. Removal of heavy metal from contaminated sites is particularly challenging task today because there are various metals which do not undergo microbial or chemical degradation Theyare toxic and their concentration remain in soil for long period of time after their introduction[3,4]. So it is necessary to make an effective and environmental friendly soil remediation approach. Methods involved in remediation of heavy metal techniques are (i) ex situ (excavation) or in situ (on-site) soil washing/leaching/flushing with chemical agents (ii) chemical immobilization/stabilization method to reduce the solubility of heavy metals by adding some non-toxic materials into the soils (iii) electrokinetics (electromigration) (iv) covering the original polluted soil surface with clean soils (v) dilution method (mixing polluted soils with surface and subsurface clean soils to reduce the concentration of heavy metals) (vi) phytoremediation by plants[5,6]. Phytoremediation is green technology which is being used for the removal of toxicity in soil. Plants can break down, stabilize or degrade organic and inorganic pollutants to detoxify soil, sediment, water and air. Phytoremediation is a low cost, solar energy driven and natural cleanup technique, which are most useful at sites with shallow, low levels of contamination. Phytoremediation harnesses natural processes to assist in the clean-up of pollutants in the environment. The mechanisms by which plants promote the removal of pollutants are varied, including uptake and concentration, transformation of pollutants, stabilization, and rhizosphere degradation, in which plants promote the growth of bacteria underground in the root zone that in turn break down pollutants. Phytoremediation is amenable to a variety of organic and inorganic compounds and may be applied either in situ or ex situ. In situ applications decrease soil disturbance and the possibility of contaminant from spreading via air and water, reduce the amount of waste to be land filled (up to 95%) and are low-cost compared with other treatment methods. In addition to this, it is easy to implement and maintain, does not require the use of expensive equipment or highly specialized personnel and is environmentally friendly and aesthetically pleasing to the public.
|ISSN||Print : 2349-7564, Online : 2349-7769|
Increasing concentration of heavy metals by industrial and natural processes is a major concern of pollution, so heavy metals need to be eradicated. Phytoremediation is a low cost, environmental friendly approach to eradicate the heavy metals. This review showed that Brassica juncea have remediatory effects on removal from contaminated soil. The ability of Brassica juncea being hyperaccumulators, to bioaccumulate heavy metal like Pb, Cd, Cu, Cr etc. can be used to eradicate metallic contaminants in the soil. There has been a large effort in the research of plants suitable for phytoremediation processes. As we restrict our study to only Brassica juneca, we observe there is variation in the published data regarding metal uptake and the mechanisms adopted by the plant. In context to chelation, citrate to a contaminated medium not only improves the uptake of heavy metals but also improves plant tolerance. Phytochelatins are also widely considered to be very important in the resistance of certain Brassica juneca to heavy metal toxicity. The role of heavy metal transporters seems to be very important in the tolerance of Brassica juneca to different heavy metals. Damage to Brassica plants is due to direct heavy metal effects or to induced oxidative stress. Frequently reported observations include stunted growth, reduced root growth and affected root morphology, affected photosynthetic activity and chlorosis, reduced uptake of water and of certain essential elements. But there is still a long way ahead to enable the establishment of a clear picture of the tolerance and defense mechanisms used in Brassica juneca.