4.6 Analysis of Various Indices
4.6.6 Enrichment Factor
94
area belongs to the class of moderate degree of contamination (2< mCD< 4). However, most of the computed value of mCD lies in the class of nil to very low contamination of soil in the waste disposal site.
95
The value of EF varies across the sites following the sequence of Sb>Cd>As>Pb>Sc>Zn>Hg>V>Co>Ti>Ba>Cu>Sr>Ni>Cr>Fe>Mn>K>Ca>Na in dry season. In rainy season, the EF varied with the sequence of Sb>Cd>Pb>As>Sc>Zn>Co>Hg>V>Ti>Ba>Sr>Cu>Ni>Cr>Fe>K>Mn>Ca>Na. Figure 4.38 shows the mean value of EF of twenty elements measured for dry season and rainy season. In dry season, EF was calculated based on forty soil samples (BH-1 to BH-40) where in rainy season EF for twenty soil samples (BH-41 to BH-60). To make a comparison of EF for all the studied metal elements and it can be concluded that the values of EF were found to be very close in both seasons. However, the dry season showed the highest value of EF than that of rainy season as well as vice versa. Figure 4.38 shows that the value of EF for the metal elements of Pb, Zn, Cd, As, Hg, Co and Sb were greater than 50 and lies in the class of extremely severe enriched. Furthermore, the value of EF for Sb and Cd showed very high EF values indicated the soil was extremely severe enrichment for both seasons. The values of EF for Ti and Ba as well as for Fe showed the class was very severe enriched and moderately enrichment, respectively, for dry season. In addition, the value of EF for Fe, Mn and K indicated the minor enrichment as well as Na and Ca indicated no enrichment in soil of the selected waste disposal site for rainy season.
Figure 4.38: Classify the level of contamination of soil based on EF for dry and rainy seasons.
0.1 1 10 100 1000 10000
Fe Mn Cr Cu Pb Zn Ni Cd As Hg Co Na K Ca Al Ti Sb Sc Sr V Ba
Enrichment factor (EF)
Metal elements
Extreme Severe Very Severe Severe Moderately Severe Moderate Minor No Dry season Rainy season
96 4.6.7 Geo-accumulation Index
In this study, to compute the values of geo-accumulation index (Igeo), 95% UCL was considered and the level of contamination for different metal elements in soil are provided in the Table 4.11. In addition, the values of Igeo for each metal element in soil for all the soil sampling points are provided in Table B.5 and Table B.6 in the Annex-B for dry and rainy season, respectively.
Table 4.11: Computed values of Igeo and contamination levels of soil in dry and rainy season
Metals Dry season Rainy season
Igeo
value
Contamination level Igeo
value
Contamination level
Fe -5.88 Uncontamineted -7.70 Uncontamineted
Mn -6.44 Uncontamineted -7.97 Uncontamineted
Cr -4.57 Uncontamineted -6.16 Uncontamineted
Cu -3.71 Uncontamineted -4.86 Uncontamineted
Pb 0.39 Uncontamineted to Moderately contamineted
-0.67 Uncontamineted
Zn -1.54 Uncontamineted -2.49 Uncontamineted
Ni -4.47 Uncontamineted -5.29 Uncontamineted
Cd 3.99 Strongly contamineted 2.89 Moderately to strongly contamineted As 0.67 Uncontamineted to moderately
contamineted
-0.67 Uncontamineted
Hg -1.64 Uncontamineted -3.03 Uncontamineted
Co -2.35 Uncontamineted -2.72 Uncontamineted
Na -8.95 Uncontamineted -10.28 Uncontamineted
K -6.67 Uncontamineted -7.81 Uncontamineted
Ca -8.33 Uncontamineted -9.13 Uncontamineted
Al -7.90 Uncontamineted -8.86 Uncontamineted
Ti -2.73 Uncontamineted -3.44 Uncontamineted
Sb 4.41 Strongly to extremely contamineted
3.67 Strongly contaminated
Sc -1.37 Uncontamineted -1.94 Uncontamineted
Sr -4.28 Uncontamineted -4.92 Uncontamineted
V -2.15 Uncontamineted -3.08 Uncontamineted
Ba -3.22 Uncontamineted -3.86 Uncontamineted
The Figure 4.39 and Figure 4.40 show the overall statistics of Igeo in soil over two seasons.
Result reveals that the value of Igeo for Pb and As showed the soil was uncontaminated to moderately contaminated for dry season, while, these metals (Pb and As) showed the soil was uncontaminated for rainy season. In consideration of the metal of Cd, the value of Igeo
97
for Cd showed the soil was strongly contaminated as well as moderately to strongly contaminated for dry and rainy season, respectively. Correspondingly, the mean value of Igeo
for the metal element of Sb indicated the strongly to extremely contaminated as well as strongly contaminated level for dry and rainy season, respectively. In overall, Igeo is distinctly variable and the soil around the waste disposal site ranges from uncontaminated to strongly and extremely contaminate with respect to analysed metal, which is also supported by (Rahman et al., 2012).
In the Figure 4.39 demonstrations the values of Igeo for Fe, Mn, Cr, Cu, Zn, Ni, Hg, Co, Na, K, Ca, Al, Sc, Sr, V and Ba in soil for dry season found to be less than zero indicated the soil was uncontaminated by these metals for the selected disposal site.
Figure 4.39: Statistics of Igeo for metal elements in soil for dry season.
Furthermore, the values of Igeo for Fe, Mn, Cr, Cu, Pb, Zn, Ni, Hg, Co, Na, K, Ca, Al, Sc, Sr, V and Ba in soil were found to be less than zero indicated the soil was uncontaminated for rainy season showed in the Figure 4.40. Moreover, only the metal element of As showed the maximum value of Igeo which was greater than zero.
The computed values of Igeo for the metal elements of Pb, Cd and As in the present study were then compared with the other researches for similar cases of studies provided in Table
-12 -10 -8 -6 -4 -2 0 2 4 6 8
Fe Mn Cr Cu Pb Zn Ni Cd As Hg Co Na K Ca Al Ti Sb Sc Sr V Ba Geoaccumulation index (Igeo)
Metal elements
98
4.12. The comparison of Igeo for Pb, Cd and As in soil presented in Figure 4.41, Figure 4.42 and Figure 4.43, respectively. These figures depicts that, Igeo for Cd was found higher in compare with Rahman et al. (2012) and Ajah et al. (2015).
Figure 4.40: Statistics of Igeo for metals in soil for rainy season.
Table 4.12: Comparison of Igeo of present study with other researchers for dry and rainy season
Parameters
Igeo
Present study Rahman et al. (2012) Ajah et al. (2015)
Dry Rainy Dry Rainy Dry Rainy
Pb 0.39 -0.67 0.06 -0.1 9 0.4 0.05
Cd 3.99 2.89 -0.03 -0.53 -1.3 -0.7
As 0.67 -0.67 3.23 2.16 0.9 0.6
The values of Igeo was computed based on the concentration of metal elements in soil. In the present study for dry season, soil samples showed comparatively the higher concentration of Pb than that of rainy season. For this reason, in dry season the soil samples showed comparatively the higher values (+values) of Igeo than that of rainy season (-values) (Figure 4.41). The present study showed comparatively the lower values of Igeo than that of published by Rahman et al. (2012) and Ajah et al. (2015) in rainy season. In addition, Ajah et al. (2015) found (+ values) of Igeo in case of rainy season.
-13 -11 -9 -7 -5 -3 -1 1 3 5
Fe Mn Cr Cu Pb Zn Ni Cd As Hg Co Na K Ca Al Ti Sb Sc Sr V Ba Geoaccumulation index (Igeo)
Metal elements
99
Figure 4.41: Comparing Igeo for Pb in the present study with other researchers for similar cases of studies.
Figure 4.42: Comparing Igeo for Cd in the present study with other researchers for similar cases of studies.
In the present study for dry season, soil samples showed comparatively the higher concentration of Cd than that of rainy season implied the higher values of Igeo than that of
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6
Present study Rahman et al. (2012) Ajah et al. (2015)
Geoaccumulation index (Igeo)
Similar studies available in literature
Dry season Rainy season
-2 -1 0 1 2 3 4 5
Present study Rahman et al. (2012) Ajah et al. (2015) Geoaccumulation index (Igeo)
Similar studies available in literature
Dry season Rainy season
100
rainy season (Figure 4.42). The present study showed comparatively the higher values of Igeo than that of published by Rahman et al. (2012) and Ajah et al. (2015) for both the dry and rainy season. In addition, Rahman et al. (2012) and Ajah et al. (2015) found (- values) of Igeo for both, dry season and rainy season (Figure 4.42). However, Ajah et al. (2015) found comparatively the lower values of Igeo than that of obtained by Rahman et al. (2012).
Figure 4.43: Comparing Igeo for As in the present study with other researchers for similar cases of studies.
In addition, Figure 4.43 reveals that Rahman et al. (2012) was found comparatively the higher values (+ values) of Igeo for As than that of results of present study and result of Ajah et al. (2015) for both seasons. The present study only showed the lowest values (-values) of Igeo for As.