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Although some heavy metals are essential trace elements, most of them can be toxic to all forms of life at high concentrations due to formation of complex compounds within the cell. Unlike organic pollutants, heavy metals once introduced into the environment cannot be biodegraded. They persist indefinitely and cause pollution of air, water, and soils. Thus, the main strategies of pollution control...
Plants are primarily exposed to metals through the soil from where they may be absorbed by root tissues and transported into the shoots. The presence of metals at toxic levels can elicit a wide range of visible and physiological symptoms in plants. In addition to deformation and discoloration of tissues, effects include inhibition of seed germination, decreased root and shoot growth, decreased rates...
Ever increasing human activities including agricultural, urban, or industrial are a major source of environmental pollution. Toxic metal pollution of waters, air, and soils is one of the potential problems, which is an enigma for scientists how to tackle this problem that has threatened the environment. To solve this, conventional remediation approaches have been used, which, however, do not provide...
Legumes have traditionally been used in soil regeneration, owing to their capacity to increase soil nitrogen due to biological nitrogen fixation. Recently, legumes have attracted attention for their role in remediation of metal-contaminated soils. Legumes accumulate heavy metals mainly in roots and show a low level of metal translocation to the shoot. The main application of these plants is thus in...
Heavy metal contamination caused either by natural processes or by human activities is one of the most serious environmental problems. Physicochemical methods such as soil washing, excavation, and reburial for heavy metal removal from contaminated soils are expensive and disruptive. Phytoremediation in contrast is a low-cost environmentally friendly and potentially effective technology for the reclamation...
Soil and groundwater are important components of agricultural and renewable natural resource (RNR) production systems. These components and production systems are influenced directly and/or indirectly by anthropogenic activities. Many of these activities have series of impacts, the negative ones being through the generation and deposition of xenobiotics that are dangerous to life forms, onto and/or...
Recent years have witnessed a considerable growth of microbiological researches in serpentine soils in relation to the presence of hyperaccumulating plants. Nickel-hyperaccumulating plants accumulate huge amounts of heavy metals in shoots, and therefore, provide a specific environment for bacterial populations and in particular for endophytic bacteria. Bacterial endophytes have been studied in many...
Heavy metal contamination of soils is one of the world’s major environmental problems, posing significant risks to human health as well as to the ecosystems. Conventional treatment technologies for heavy metal polluted soils such as excavation and transport of contaminated soil to hazardous waste sites for landfilling have several disadvantages. They cannot completely remove metals, they can only...
Mycorrhizal fungi, obligate biotrophs, form mutualistic associations with plants and provide mainly phosphorus to plants. Mycorrhizal fungi colonize the roots of many plants growing on metal-contaminated soils and play an important role in metal tolerance and accumulation. Even though mycorrhizae are known to inhabit metal contaminated sites; the exact mechanism of colonization is unclear. For example,...
Metal stress restricts plant growth and distribution and has become a widespread problem. Plants can respond to toxic metals in a variety of ways, but the most important of them is the production of phytochelatins (PC). The knowledge of how plants perceive metal presence and switch on or off the PC synthesis pathway could help understanding the metal tolerance mechanisms in plants. This knowledge...
Contamination of soil with heavy metals poses a major environmental and human health problem. Of the various metals, cadmium and arsenic are the two well-known heavy metals. The toxic effects of these metals are due to their abundance while nonbiodegradable nature leads to their concentration buildup in soil. Microbial methods of environment purification and cleanup are promising because of the safety,...
Soil contamination by toxic metals is a major problem that has threatened the sustainability of various agro-ecosystem worldwide. Generally, heavy metals are not destructed and, therefore, persist in the environment. The traditional physical and chemical methods applied for metal removal from contaminated sites produce undesirable products and are expensive. The bioremediation methods including phytotechnologies,...
Chromium, a steel-gray, lustrous, hard, and brittle metal, occurs in nature in bound forms and has been widely used in various industries. Chromium exists in several oxidation states, of which hexavalent chromium is a priority toxic, mutagenic, and carcinogenic chemical, whereas trivalent form is much less toxic and insoluble. Hexavalent chromium causes various chronic health disorders including organ...
The soil environment is a major sink for multitude of chemicals and heavy metals, which inevitably leads to environmental contamination problems. Indeed, a plethora of different types of heavy metals are used and emanated through various industrial activities. Millions of tonnes of trace elements are produced every year from the mines in demands for newer materials. On being discharged into soil,...
Remediation techniques for soils polluted with toxic metals can be divided into two main groups: immobilization and soil washing. Immobilization technologies leave metals in soil, but minimize their availability, while soil washing with chelating agents removes metals from soil. Metals in soil are not entirely accessible to chelating agents and, hence, not entirely removed. Residual metals left in...
Heavy metal contamination of aquatic ecosystems has been increasing in recent times, owing to disposal of such pollutants in effluents. Their presence to excessive levels leads to serious health problems in living organisms, since they cannot be mineralized to completely innocuous forms. The physicochemical methods, such as chemical precipitation, chemical oxidation/reduction, or ion exchange, employed...
Radionuclides exist in the environment naturally and, in more recent times, have been added by nuclear power and weapons. The carcinogenic nature and long half-lives of many radionuclides make them a potential threat to human health. Moreover, there is an increasing trend of uranium accumulating in soils due to a number of deliberate or wrong practices. Also, the contamination of land by naturally...
Use of plants to remediate soil contaminated with heavy metals has received an increasing attention during the last decade. Bioremediation using living plant species, referred to as phytoremediation, covers several different strategies, of which bioremediation employs phytoextraction, rhizofiltration, phytostabilization, and phytovolatilization. High efficiency, low cost, and easy operation make phytoremediation...
Phytoextraction is an environmentally sound and cost-effective technology for cleaning up soils contaminated with toxic metals. The success of phytoextraction depends on the ability of plants to produce large amounts of biomass. In addition, plants must be tolerant to the target metals and be efficient to translocate metals from roots to the aboveground organs. The effectiveness of phytoextraction...
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