**3. Methods for the characterization of heavy metals in phytoremediation**

The different techniques applied for the characterization of heavy metals are presented in **Table 1**.

One of the techniques that can be used for the identification of heavy metals is Atomic Absorption Spectroscopy (AAS), this analytical technique is widely used to determine more than 70 elements in solution and in different matrices, in quantities as low as 10–14 g with reasonable selectivity, little manipulation, and minimum sample size. It can indirectly identify anions and organic compounds [33, 34]. This technique is older than ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy), and various authors have reported studies comparative with other methods cited in environmental regulations [12, 28, 38], some mention that it makes it possible to quantitatively determine the chemical elements that constitute a material quickly, precisely, and accurately [7, 13, 39].

To convert solid and liquid samples into aqueous solutions for analysis with ICP-OES and AAS, it is necessary to eliminate all organic material to avoid interferences and obtain the analytes of interest at detectable concentrations [12, 38, 40–43]. Acid digestion is a necessary process in the identification of metals, which is done by acid decomposition at high temperatures [36] or using mixtures of HNO3 and H2O2 [37].

Another method used is X-Ray Fluorescence spectroscopy (XRF). It can identify analytes or other components of interest and it is thus very useful for qualitative analysis. It is currently used in the fields of archeology, forensic sciences, medicine, geology, coatings, materials, electronics, pharmaceutics and environmental sciences, used this method to perform qualitative and quantitative analyses of heavy metals [35, 44].


**Table 1.**

*Techniques for characterization of heavy metals.*

## **4. Vetiver: potential use in phytoremediation**

Several authors have achieved the mitigation of different types of heavy metals using vetiver grass (**Table 2**) and determined the amount of Cr absorbed from the residual sludge of a tanning facility and found a concentration of 596.92 mg kg−1 in the leaf tissue [38], others studies showed that the effect on vetiver of having a concentration of As of 225 mg kg−1 is a slight yellowing of the leaves and a small decrease in biomass [36]; these results confirm that this grass can survive successfully in soils moderately contaminated by As [31].

The capacity of vetiver to remove contaminants has also been tested using compost leachate, an experiment that was allowed to stand for 112 days without

#### *Biodegradation Technology of Organic and Inorganic Pollutants*


**Table 2.**

*Heavy metals absorbed for vetiver grass.*

aeration, showed that the concentration of Cd, Cu, Fe, and Pb decreased after the treatment with vetiver, and therefore can be used to for the bio-purification of compost leachate [42]; others study evaluated the efficiency of vetiver in the absorption of metals based on the translocation and bioaccumulation factors, the results revealed that roots have a high uptake capacity for Cd, Pb, and Zn, however, there was a low translocation of metals such as Cd, As, Ni, and Pb towards the aerial part of the plant and accumulation of Zn in the roots was the highest at 100% [28].

However, some similar reports found a highs amount of Fe accumulated in the roots, despite this, the results show that vetiver is a good phythostabilizer and potential accumulator of heavy metals since in the roots they also found the presence of Al, Cu, Mn, Zn, Cr, and Ni, but in concentrations, inferiors to Fe [13]. In research similar, the absorbed metals were found to be in order Fe > Pb > Cu > Mn > Zn, the results also showed that as the length and density of the roots increases, so does the absorption of heavy metals, but suggest being careful if in the site intends to develop other species, due to the competition of Fe and its importance in the physiological processes of plants [12].

In 2007, a study assessed the efficiency of the vetiver grass in the phytoextraction of Cr, Cu, Pb, and Zn in order to establish whether this plant could be considered a good hyperaccumulator of those heavy metals. Phytoextraction experiments showed that vetiver was little efficient in the uptake of Cr and Cu (less than 0.1% in shoots and roots after 30 days for both metals), but highly efficient in the uptake of Pb and Zn (0.4% in shoots and 1% in roots for Pb and 1% in both shoots and roots for Zn, after 30 days), for these reasons, vetiver grass can be considered a good enough "hyperaccumulator" of Pb and Zn [41].

In 2013, other researchers measured the ability to remove heavy metals from industrial wastewater. Vetiver were grown on four samples of industrial wastewater taken from a milk factory, a battery manufacturing plant, an electric lamp plant, and an ink manufacturing plant, the results indicated that could tolerate and grow in wastewater [24].

On the other hand, some studies have evaluated the efficiency of vetiver in the treatment of leachates with the aim of reducing chemical oxygen demand, total suspended solids, total dissolved solids and total organic carbon in municipal landfill leachates. The results revealed a removal efficiency of approximately 90% [45]. A relevant study evaluated the differences in tolerance and accumulation of boron between reed (*Phragmites australis* L.), cattail (*T. latifolia* L.) and vetiver, these plants survived concentrations of B of up to 250, 500, and 750 mg L−1, respectively, therefore, vetiver showed the highest tolerance to B [40]. Thus, the evidence described above confirms the phytoremediation potential of the vetiver

*Phytoremediation Potential of* Chrysopogon zizanioides *for Toxic Elements in Contaminated… DOI: http://dx.doi.org/10.5772/intechopen.98235*

grass, the findings of different studies have confirmed the potential of vetiver as a phytoremediation plant for use in the removal of heavy metals from contaminated soils [12, 46, 47] and in the rehabilitation of landfills [35]. Although it is not an aquatic plant, vetiver can grow and survive under hydroponic conditions [48] and can be used to remediate eutrophic waters, wastewater from pig farms [49], and waste leachates [50].

Further studies could focus on increasing the uptake of heavy metals using, for example, chelating agents [41] and explore the ability of vetiver to participate in the remediation of other pollutants such as endosulfan [49]. The dense growth of vetiver roots can prevent erosion and landslides and act as a natural barrier that could be used in landfill cells to prevent leachates from infiltrating the aquatic mantle, regardless of the impermeable barrier (geomembrane) that is commonly used in landfills.
