# Fire-Induced Changes in Soil and Implications on Soil Sorption Capacity and Remediation Methods
## 4 Fire-Induced Changes in Soil and Choice of Soil Remediation Technologies
### Biological Remediation Methods  
#### Phytoremediation  
Phytoremediation, also referred to as botanoremediation, vegetative remediation, green remediation or agro-remediation, uses green plants to fix or adsorb contaminants from the soil environment [136]. It involves three mechanisms: phytostabilization, phytovolatilization and phytoextraction. In phytostabilization, plant roots immobilize contaminants through several methods, which may include reduced soil erosion due to stabilization of soil by plant roots, reduced leaching through upward water flow generated by plant transpiration, and decrease in runoff due to above-ground vegetation [136]. The contaminants accumulate in the roots of plants (phytostabilizers), or are immobilized in the rhizosphere of the plant. A main characteristic of phytostabilizers is that they are able to accumulate high levels of contaminants, especially heavy metals, from the soils in their roots, but the translocation of these metals to their aerial parts is limited. The contaminant concentration in the contaminated soil is reduced usually only around the rhizosphere of the plants involved and therefore need monitoring to ensure that optimal stabilizing conditions are maintained [135]. Phytovolatilization, which is another form of phytoremediation involves the transfer of contaminants from the soil to the atmosphere by converting them into a volatile state [135]. According to [PERSON] et al. [149], contaminants are taken up from the soil by plants and converted into less toxic vapors which are released into the atmosphere through the process of transpiration. Examples of plants with phytovolatilization potential include _Arabidopsis thaliana_, _Brassica juncea_ and _Chara canscens_. Mercury is the most widely studied contaminant remediated through phytovolatilization. Its presence in some mining environments may validate the use of phytovolatilization as a remediation method. Most plants, however, lack the ability to volatilize contaminants like mercury, and so plants used as phytovolatilizers are usually genetically modified to improve the _merA_ gene, which codes for mercuric ion reductase. This enzyme is the catalyst involved in the conversion of Hg\({}^{2+}\) to elemental mercury (Hg(0)), a volatile, non-reactive, and less toxic form of mercury. Through this, mercury in contaminated environments can be cleaned up. A major concern with this method of remediation is what happens to the contaminant after it is released into the atmosphere, and the associated environmental and human health implications. In phytoextraction, tolerant plants extract and accumulate contaminants from the soil, preventing them from spreading in the environment. Phytoextraction could be continuous otherwise known as natural or chemically enhanced [150]. Natural phytoextraction makes use of plants with a high ability to accumulate contaminants. Generally, plants are usually not able to sustain growth under high levels of pollution and so phytoextraction is feasible only where sites are polluted by low to moderate levels of contaminants. These plants, also called hyperaccumulators, accumulate contaminants in their shoot tissues (without showing any symptoms of toxicity) to levels far above those present in the soil or in non-accumulating plant species. According to [PERSON] et al. [136], hyperaccumulators must have high metal-accumulation capability in their above-ground parts, must be able to tolerate high concentrations of contaminants, and should have the ability to grow fast with high biomass and a profuse root system. More than 450 hyperaccumulating plant species from 45 families (representing less than 0.2% of all angiosperms) are known. Though most of these plants hyperaccumulate and hypert tolerate only one metal contaminant, some species have the ability to tolerate more than one.