**10. Selenium phytoremediation**

Phytoremediation is a plant-based technology, which is eco-friendly, cheap and used in the treatment of contaminated soil and water resource [70, 84]. It does not reduce the fertility of the soil and this method of decontamination of the soil has been enhanced by the use of genetic engineering. Certain plants are suitable for phytoremediation, these plants are selected based of certain factors such as:


#### **10.1 Methods of phytoremediation**

There are various methods of phytoremediation, but phytovolatilization, rhizofiltration and phytoextraction are the most stable of selenium decontamination of soil and water bodies [70].

#### *10.1.1 Photoextraction*

Phytoextraction is the use of higher plants which are se-hyperaccumulators in the removal of se-contaminates from the soil [70, 86]. These se-hyperaccumulator plants grow on seleniferous soil and they are able to accumulate up to 15,000 mg/kg selenium. These plants are cultivated on the contaminated soil then after they have successfully removed the se in the soil they are disposed of. The main drawback of the method is that these se-hyperaccumulator plants grow slowly; this makes this strategy time consuming. They also have limited biomass production this leads to insufficient selenium decontamination for the soil [87].

#### *10.1.2 Phytovolatilization*

Phytovolatilization is the process of plants absorbing contaminants from the soil and releasing it to the atmosphere. Green plants are able to convert inorganic forms of selenium which are toxic to a less toxic organic selenocompounds [70]. This method is advantageous over phytoextraction, because it does not require the disposal of contaminated plant. The particular volatile selenium released by sehyperaccumulator plants is dimethyldiselenide, while nonaccumulator plants release dimethylselenide from its leaves [88]. A more efficient method of phytoremediation is the combination of phytovolatilization and phytoextraction. This method increases the se-decontamination of soil by 2–3 times more than when carried out individually. Phytovolatilization method depends on certain factors such as the specie of plant, the microorganism in the rhizosphere, the selenium specie, temperature and so on [89].

#### *10.1.3 Rhizofiltration*

This strategy uses plant roots to decontaminate flowing water. It uses plant biomass to remove the contaminants as in the case of phytoextraction. Although they share same principle, rhizofiltration is used to decontaminant strictly water bodies and it involves the disposal of the root and shoot of the contaminated plant unlike phytoextraction which is only used to decontaminate the soil and involves the disposal of only the shoot of the contaminated plant.

#### *10.1.4 Selenium biofortification*

Selenium biofortification is a method used in the disposal of waste plants by decomposition [90, 91]. The selenium present in the plant is used to enrich the soil

### *Uptake, Metabolism and Toxicity of Selenium in Tropical Plants DOI: http://dx.doi.org/10.5772/intechopen.90295*

which aids in improvement of food quality [92]. Biofortification is an agricultural practice used in enriching food productions with different nutrients such as selenium in this case, with the purpose of increasing dietary intake by various biotechnological methods such as genetic engineering, plant breeding and manipulation of agronomic practices practices (Kieliszek and Blazejak, 2012) [93, 94]. Genetic engineering is a useful method of obtaining Se-biofortified food products, this is carried out by manipulation of selenium-related enzymes for uptake, evaporation and assimilation of selenium. Biofortification is cheap, safe and it also helps in carving out various nutrient deficiencies in diets [95–97]. Selenium biofortification is used to increases selenium contents of farm produces, this helps reduce selenium malnutrition among a population.
