**8. Remediation of Hg-contaminated soils and water**

Increasing Hg emissions due to anthropogenic activities caused severe soil pollution issues [44–46]. As a crucial link between the atmosphere and water, soil plays

#### *Perspective Chapter: The Toxic Silver (Hg) DOI: http://dx.doi.org/10.5772/intechopen.111464*

a central role in the global Hg cycle [47]. Soil is not only an Hg sink, receiving Hg input from the environment but also reemitting it to the atmosphere [48, 49], water [42, 50], or the plants grown thereon [39].

Mercury, like other potentially toxic elements, is not biodegradable, and therefore, its remediation should encompass either removal from soil or immobilization [32]. The main Hg removal technologies are physical and chemical remediation methods, as well as bioremediation technology. Adsorption of Hg2+ and Hg(0) from water on surfaces of high surface area and high porosity such as chitosan derivatives, synthesized thioether-functionalized covalent triazine nanospheres, pentasil zeolite (type ZSM-5), and utilized silica-coated magnetic nanoparticles are the most common physical approaches for remediating Hg-contaminated soil [51]. Other techniques could help such as soil replacement, physical separation, soil vapor extraction, fixed/stabilized soil, vitrification, thermal desorption, and electrokinetic remediation technology [6]. The latter technique (electrokinetic remediation) depends on passing a direct current between electrodes through the soil to make the Hg ions move through an ion exchange membrane from the soil to the electrodes. The addition of chelating agents to soil could effectively increase the solubility and removal efficiency of Hg [6]. Recently, He and his research group introduced a novel *in situ* immobilization technology by injecting stabilized iron sulfide nanoparticles into soil to immobilize Hg [32].

The *in situ* thermal desorption is a promising technique of Hg remediation that does not need to dig up the contaminated soil; instead, thermal conductive heating (TCH) elements are inserted into the soil in order to directly transfer heat to above 600°C to volatilize various species of mercury, such as HgO, HgS, HgCl2, and mercury associated with organic matter and thus achieve an acceptable decontamination level [51].

Biological remediation/bioremediation depends on plant and microbial in remediation soils [6]. In particular, genetically engineered plants can change methylmercury complexes, and mercury ions into metallic forms of lower toxicity, and then extract, detoxify, and/or sequester this contaminant from soil and water [10]. Phytoremediation is an umbrella term, which refers to the different low cost and ecofriendly technologies that utilize plants in decontaminating areas [52]. This includes: phytostabilization, phytoextraction, and phytovolatilization. This *in situ* application of phytoremediation lessens the disturbance of the surrounding environment and also declines the spread of contamination *via* air and water [32]. There are many other technologies such as the use of nanoparticles to remove/absorb Hg from soil, water, and flue gas, owing to their high adsorption capacity, small dimension, and other unique electrical, mechanical, and chemical properties [53].

Continuous monitoring of Hg levels in air, soils, water, and foods is necessity to ensure their sustainable safe use in order to protect human health and the surrounding ecosystem. In addition, increasing the awareness of humans about the danger of Hg is a proactive step to prevent and reduce the danger of Hg pollution. Furthermore, remediation protocols should be followed in Hg-contaminated areas to lessen its toxicity.
