**2.11 Molybdenum (Mo)**

In the plants sampled measured for Mo in autumn and summer, it was found that Mo was highly accumulated by the plants in autumn. The average concentration for Mo measured in autumn was 0.09 μg/g and in summer was 0.07 μg/g, as portrayed in **Figure 16**.

#### **2.12 Lead (Pb)**

The average concentration for Pb in the summer and autumn months was 12.082 and 12.084 μg/g respectively as shown in **Figure 17**. Higher concentrations for Pb were measured in the plants in summer.

**Figure 16.**

*Variation in the average Mo concentration accumulated by plant in summer and autumn.*

**Figure 17.** *Variation in the average Pb concentration accumulated by plant in summer and autumn.*

*The Evaluation of the Macrophyte Species in the Accumulation of Selected Elements… DOI: http://dx.doi.org/10.5772/intechopen.105708*

#### **2.13 Statistical significance of elements between water, sediments, and plants**

The correlation coefficients were performed to determine the relationship between the levels at which the elements were absorbed by the three species of *Schoenoplectus, Phragmites,* and the *Typha spp*. The concentrations of elements in the water, sediments, and plants were compared by the use of the significant variance at p = 0.0500. When the significant correlations coefficient was performed, several significant correlations were found to take place between the plants, water, and sediment. A correlation was found between sediments and plants, where Magnesium was negatively correlating with Cr and Fe and positively correlating with P, S, Mn, Co, and Ni. Their associated r values were (Cr) r = 0.06143 and (P) r = 0.6232. The r values for the positive correlations were (P) r = 0.7598, (S) r = 0.6406, (Mn) r = 0.8714, (Co) r = 0.8021 and (Ni) r = 0.6704. The p values were significant at p = 0.0500 and all the p values were in arrange of p = 0.000 and 0.0015.

P was found to be having both negative and positive correlations with the elements in water, sediments, and plants. The negative correlations were found between the concentrations of Cr, Fe, and Pb while the positive correlations were obtained between the concentrations of Mn and Co. The r values of the elements with negative concentration correlations were (Cr) r = 0.6488, (Fe) r = 0.7973 and (Pb) r = 6581, while the correlation for the elements with positive concentrations of elements were (Mn) r = 0.07636 and (Co) r = 0.7841. Their p-values were significant at p = 0.0500 and their p values were in arrange of p = 0.000 and p = 0.009 in water, sediments, and also in plants. Cr was also found to have a negative correlation with Mn and positive correlations with Fe and Pb.

The correlations were significant at p = 0.0500 and the p values were in a range of p = 0.000 and p = 0.038. The correlations were (Mn) r = 0.5389, (Fe) r = 0.8005 and (Pb) r = 0.8584 respectively in water, sediments and plants respectively as shown in **Appendix 1**.

#### **2.14 Translocation and bioconcentration factors of sediments and plants**

Bioconcentration factor is defined as the ratio of metal concentration in plant aboveground part to the total metal concentration in the soil. The translocation factor is the ratio of metal concentration in the shoots to the metal concentration in the shoots. Bioconcentration of elements of the plants'species between the seasons. Since the amounts of elements enter the aquatic ecosystem after being washed from the mine dump, the elements (some of which are toxic) become accumulated in the water column, in the sediments, and also uptake by the plants which then pose some health threats when accumulated in higher amounts. Bioconcentration factor (BCF) is described as the measure of the amount of an element accumulated in the plants from their surrounding environment that is in contact with it [26]. It can be obtained by dividing the trace element concentration in plant tissues harvested by the initial concentration of the element in the external nutrient solution. Translocation factor (TF) on the other hand is defined as the ratio of element concentration in the root to shoot (**Table 4**) [27, 28].

This resulted in BCFs for the different types of plant organs (**Table 4**). The BCF for the shoots, rhizomes, and leaves was calculated from the elements accumulated by the plants in both the summer and autumn seasons.

**Table 4** below shows the TF and BCF of quantified elements in the study. In both seasons, elements that were mostly taken with high BCF were S, Mg, Zn, Mn, P, Cu,

Ni, and Co, and elements that were mostly taken with the highest TF were P, Mg, S, Cr, Zn, Pb, Cu, and Mn. In autumn, the plants' organs that were found to have the highest BCF were the leaves of *T. capensis* and *P. communis* as well as the roots of *Scirpus corymbosus.* In summer, the highest BCF was obtained in the roots and rhizomes of *P. communis* and *S. corymbosus*. In summer, the plant species with the highest BCF and TF was *S. corymbosus;* and in autumn,*T. capensis* was the plant species with the highest BCF while *S. corymbosus* was the plant species with the highest TF. It was observed that both the TF and the BCF are affected by seasonality. The TF was higher in the autumn season than in the summer season, and the BCF was higher in the summer season than in the autumn season. It became evident that BCF active growth of the plants in summer as most of the elements are used by the plants during processes such as photosynthesis which is active in green leaves compared to when the plants' leaves start drying up and photosynthesis ceases and most element losses occur, as the leaves die off and become brittle.

When making comparisons of the results of the translocation, Bioconcentration factors for plants and sediments, it was found that P, S, Mn, Mo, and Pb were lower in all three plant species and higher in the sediments. On the other hand, elements such as Mg, Cr, Fe, Co, Ni, Cu, and Zn were accumulated in higher concentrations by the plants and lower in the plants.

The results for TF and BCF indicate that the investigated plants accumulate in higher concentrations of certain elements and some in smaller concentrations. The elements that were found to be accumulated in lower concentrations by the plants were on the other hand found to be accumulated at higher concentrations by the sediments. This could be the case where the plants release the elements back into the substratum when they die off. This was observed in the accumulation of Molybdenum, where the measured Mo concentration was below the detection level by the plants. The plants with high BCF were regarded as suitable to be used to decontaminate soils. Although the plants showed high BCF, they still do not meet the criteria of being hyperaccumulators. The plants accumulated levels of elements such as Cu, Zn, and Pb in amounts with higher BCF (92.40, 200.79, and 17.55 in summer and 30.65, 76.14, and 11.98 in autumn) but the concentration of these elements was not greater than 1000 mg/kg to be regarded as hyperaccumulators. The plants were regarded as moderate accumulators [26]. The plants were suitable to be applied in contaminated soils for phytoremediation processes [29].

#### **2.15 Comparison of elements in water with the international organizations**

**Table 5** illustrate the current drinking water quality guidelines by international organizations, and for the basis of this study, the levels of elements in water were compared with the water quality guidelines to indicate whether the level of elements in water was either above or below the required or acceptable levels. The last column indicates the concentration levels of elements measured in the water sample sites of this study.

Zn concentration in water was within the acceptable range of 267 μg/l, and when compared with the international guidelines for water quality standards which were above 500 μg/l. Fe, Ni, Mn, and Cu were found to be highly concentrated above the acceptable levels in water when compared to the international water quality guidelines, with the concentration levels of 2230, 282, 5900, and 14,080 μg/l respectively. The units for the elements concentrated in water were illustrated in μg/l in this section to easily compare with international guidelines as the standards were expressed in μg/l

*The Evaluation of the Macrophyte Species in the Accumulation of Selected Elements… DOI: http://dx.doi.org/10.5772/intechopen.105708*


*a World Health Organization (WHO 2011).*

*b United States Environmental Protection Agency (USEPA, 2011).*

*c European Commission Environment (ECE, 1998).*

*d Federal-Provincial-Territorial Committee on Drinking water (CDW), Health Canada (FTP-CDW, 2010).*

*e Pakistan Council of Research in Water (PCRWR, 2008).*

*f Australian Drinking Water Guidelines (DDWG, 2011).*

*g Norma Official Mexicana NOM-127-SSA1–1994 (DOF, 1994).*

#### **Table 5.**

*Drinking water quality guidelines (μg/L–<sup>1</sup> ) for elements in water in this study.*


#### **Table 6.**

*Summary of descriptive statistics of elements accumulated by sediments.*

rather than in mg/l as shown in **Table 6**. To evaluate the effectiveness of these macrophytes in the accumulation of selected elements, a study of the whole life cycle of the plants has to be conducted, to capture all the processes that the plants undergo to survive the heavy metal contaminated environment. Amongst the three macrophytes investigated, there is no single plant that accumulates more than four elements than the other plants. In this study, it was observed that there are elements that are highly accumulated by either the roots, and less by the rhizomes, and more by the leaves and less by the roots. The rate of metal accumulation between the plants as well as the plant parts varies between the two seasons of autumn and summer investigated. This indicates that this could be a result of the functionality of the elements during the period of maximum absorption.

Although the plants were found to accumulate the elements investigated, it is clear that some factors lead to the plants not uptake some elements in higher concentrations than the others. This creates a knowledge gap in this study, and as a result, further studies should be undertaken to investigate the reason the plants accumulate certain elements in lower concentrations. Another factor to be investigated is the overall performance of the plants in elements uptake throughout the whole growth cycle, and the results of such a study could be able to fill the gap in this study.
