**6.4 Addition of chelating agents**

The increase of the uptake by crops can be influenced by increasing the bioavailability of radionuclides through addition of biodegradable physiochemical factors such as chelating agents, and micronutrients [39].

In a stressed environment, the application of plants to remediate sites governed by mainly on the persistence capacity of the plant. All through phytoremediation, plants absorb pollutant from the soil, and mineralized it, thus preventing infection of groundwater and retaining system shield for human habitation. Efe and Elenwo reported that plants (e.g., *Axonopus compressus*) used as phytoremediation means, should have the capacity to adapt properly to the climatic condition and soil of the polluted sites, and retain high patience under stressed environments [40]. Several phytoremediation plant types have technologically advanced adaptive features for absorption, acceptance, transfer and degradation of pollutants for example heavy metals, crude oil, explosives, and radionuclides [41].

The efficiency of the process is also dependent on the soil properties, type of contaminants and its bioavailability. Plant roots usually serve as interlinks providing enormous surface area for the absorption and accumulation of essential growth nutrient along with contaminants [42]. In metal contaminated sites, characterization of eco-toxicity (e.g., oxidative stress) is mostly determined through the formation of free radicals [43]. Some of the advantages of phytoremediation include risk containment, extraction of valuable metals (phytomining) and increased soil fertility/quality.

Baker and Brooks [44] recommended that the metal hyperaccumulator must fulfill a standard that the concentration of an element stored in a plant can be higher than the soil [44]. Based on their classification, the transfer factor (TF)

can be defined as the ratio of target element concentration in the plant to that in the tailings.

 Transfer factor = (target element concentration in the plant)/ (target element concentration in the tailings). (1)

TF can be used as an index for the growth of a target element in the plant and its transfer from the tailings to the plant. If TF for a plant is greater than 1 and the amount of the target element collected in the plant is relatively small, the elimination competence of the plant for that target element can be further improved by a number of breeding practices, and can further implemented in phytoremediation [45].

Different TF values for the plants tissues may be resulted in part from metabolic rate differences between plant species and cultivations [46]. The factors for example the concentration of a radionuclide, pH, plant age, and ecotype may adjust the uptake and ratio of the content of the element present in the plant shoot to that in its root [47]. About 91 tissues of plant species had the TF values of <1, only 9 tissues of plant species had the TF values of more than 1. Overall, it was found that most of the plant species inspected had low experiences of removing U, Th, and 226Ra from the stakeouts to the plant tissues. The results were friendly with the earlier research results [48–52].

In summary, phytoremediation of goal radionuclides from the followings largely depends primarily on three parameters with the radionuclide concentration in the plant, the plant biomass, and the target radionuclide concentration in the investigations. In order to assess the potential of a plant for phytoremediation more broadly, a novel coefficient was anticipated and named as phytoremediation factor [53]. This factor is the ratio of the total amount of a target radionuclide accumulated in the plant shoot to the concentration in the tailings at the site where the plant grows.

Phytoremediation factor (PF)

 = (target radionuclide concentration in the plant shoot)/ (biomass of the plant shoot Target radionuclide concentration in the tailings). (2)

In this formula, the shoot refers to the tissue above ground of the plant including the seed, leaf, and stalk. The PF can be used as an index for the capability of a plant to remove the target element from the tailings.

The results indicated that PF was agreeable with the plant removal capability. PF extends the conventional definition of hyperaccumulator, and it can easily be obtained. Although the concentration of a target radionuclide in a plant does not fulfill the criteria for a hyperaccumulator, if the plant has relatively high biomass, the plant may also be deliberated as the candidate for phytoremediation. Keeping in view the phytoremediation factor, *P. australis* and *M. cordata* were designated as the contenders for phytoremediation of uranium-contaminated soils [53, 54]. Azolla imbircata was selected as the candidate for phytoremediation of uraniumcontaminated water [55, 56]. *P. australis* was selected as the candidate for phytoremediation of thorium-contaminated soils [53]. *P. multifida* was selected as the candidate for phytoremediation of 226Ra-contaminated soils [54–56]. While PF offers a unique place for identification of a plant proficient in remediating the contaminated by the radioactive nuclides on a large scale, except the plant biomass per unit area. It is essential to consider further research should be executed to improvise this factor.

**37**

*Phytoremediation of Hazardous Radioactive Wastes DOI: http://dx.doi.org/10.5772/intechopen.88055*

Waste disposal is dumping waste with no objective of retrieval. Waste management means the whole structure of operations starting with generation of waste and ending with disposal. The per capita use of electricity is correlated to the living standard of a country, whereas, the electricity generation by nuclear resources can be viewed as a least degree of radioactive waste that is produced and the allied scale of radioactive waste management of the country. On the gauge of electricity generation by nuclear fuel, India need to improve a lot. In 2000, India's stake of nuclear electricity generation compared to total electricity generation was 2.65% related to 75% of France which ranks first according to IAEA Report. Hence the magnitude of radioactive waste management in India could be miniscule compared to that in

As more power reactors come on stream and as weaponization takes profounder

routes the needs of radioactive waste management increase. Radioactive waste management has been a crucial degree in the whole nuclear fuel cycle. Low and intermediate-level radioactive wastes rise from operations in reactors retained as

Solid radioactive waste is compressed, incinerated are subject to the nature of the waste. Underground drains in disposal facilities are applied for solid waste

High efficiency particulate air (HEPA) filters are used to reduce air-borne radioactivity. From the last four decades radioactive waste management facilities have been set up at Trombay, Tarapore, Rawatbhata, Kalpakkam, Narora, Kakrapara, Hyderabad and Jaduguda, accompanied by the growth of nuclear power and fuelreprocessing plants [57–63]. Numerous barrier methodology is monitored in solid

Source reduction ➔ Recycling ➔ Treatment ➔ Disposal. (3)

For the phytoremediation of radioactive waste, screening of the appropriate plant type is the utmost important. Diverse factors such as radioactive waste characteristics, the concentration of a target radionuclide in the radioactive waste, the biomass of the plant, the plant species and plants composition in the radioactive waste dumped area, the concentration of a target radionuclide in the plant, and

The PF concern the concentration of a goal element in a plant, the shoot biomass, and the concentration of the target element in the tailings or tailing (root) of the plant, was planned for the target element to specify the removal capability of the plant from the radioactive waste. Using the PF as the criteria, *P. australis*, *M. cordata*, and *Azolla imbricata* were selected as the contenders for phytoremediation of uranium-contaminated soil, *P. multifida* was particular as the aspirant for phytoremediation of 226Ra-contaminated soil, and *P. australis* was designated as the

Further advances must be made in the application of environmental remediation

to selectively eradicate materials, the concentrations of chemicals present in the contaminated water, have a higher resistance to changes in pH, greater stability for a

sludge after chemical treatment and fuel reprocessing practices.

waste handling in the next flow process are given below (eq. (3)):

Flow process for management of waste reduction [57].

contestant for phytoremediation of thorium-contaminated soil.

longer period of time and cost effectiveness.

**8. Conclusion and future directions**

should be examined thoroughly.

disposal under continuous surveillance and monitoring.

**7. Phytomanagement**

other countries.
