4.7 Spatial Distribution of Various Indices
4.7.1 Contamination Factor
The spatial distribution of contamination factor (CF) for twenty one metal elements during dry season and rainy season were performed. According to the definition of CF, the magnitude of CF for an element mainly depends on the values of metal concentration in soil and the background concentration of the metal. Earth crustal values were considered as the background of a metal element in this research work and the values are constant in all
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sampling stations. So the CF values are different than metal concentration but the distribution pattern for metal element based on concentration and CF values. The spatial distribution of CF for the metal elements are described in the following figures except Mn, Cu, Pb, Ni, Co, Na, K, Ca, Al, Sc, Sr, V and Ba in soil which are presented in Figure E.1 to Figure E.13, respectively, in the Annex-E.
4.7.1.1 Iron
The spatial distribution of contamination factor (CF) for the metal element of Fe in soil for dry and rainy season is presented in Figure 4.49 (a) and Figure 4.49 (b), respectively. The magnitude of the CF of Fe for soil sample from central point (approximately 0 m) ranges from 0.0329 to 0.0353, while, for soil sample from farthest point (390m from central point) ranges from 0.013 to 0.0155 for dry season. In rainy season, CF ranges from 0.0112 to 0.0121 for soil sample from near to centre (approximately 30 m) and 0.0029 to 0.0039 for soil sample from farthest point (315m from central point). The distribution patterns indicate that the CF of Fe in the selected site gradually decreases from the centre to the outer side area in both seasons. The ranges of concentration in both season show, the dry seasonal CF values in soil was higher than rainy season.
Figure 4.49: Spatial distribution of CF of Fe in (a) dry season and (b) rainy season.
4.7.1.2 Chromium
Figure 4.50 (a) and Figure 4.50 (b) illustrate, metal enhancement maps plotted CF distribution for Cr during dry and rainy season, respectively. The magnitude of the CF of Cr for soil sample from central point (approximately 0 m) ranges from 0.078 to 0.0822, while,
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for soil sample from farthest point (390 m from central point) ranges from 0.0437 to 0.048 for dry season. Besides, CF of the same metal ranges from 0.0501 to 0.0553 for soil sample from near to centre (approximately 30 m) and 0.0077 to 0.0-13 for soil sample from farthest point (315 m from central point) in rainy season. In figures, the deep blue colour indicated the CF of Cr in soil of that sampling point was very high, while, the yellow colour indicated the CF of Cr in soil of that sampling point was comparatively very low. Form figure, it is clear that the maximum values of CF range in dry season not only covers the centre point of the disposal site but also the surrounding area of the site. The distribution patterns are similar in both season but the CF of Cr is decreasing with lateral distance from the centre point of the area. The ranges of concentration in both season show, the dry seasonal CF values in soil was higher than rainy season.
Figure 4.50: Spatial distribution of CF of Cr in (a) dry season and (b) rainy season.
4.7.1.3 Zinc
The spatial distribution of contamination factor (CF) for the metal elements of Zn in soil (forty soil samples) for dry and rainy season is presented in Figure 4.51 (a) and Figure 4.51 (b), respectively. The CF of Zn for soil sample from central point (approximately 0 m) ranges from 0.66 to 0.699, while, for soil sample from farthest point (390m from central point) ranges from 0.343 to 0.382 for dry season. Besides, CF of the same metal ranges from 0.328 to 0.347 for soil sample from near to centre (approximately 30 m) and 0.169 to 0.189 for soil sample from farthest point (315 m from central point) during rainy season. The distribution patterns of CF were similar in both season but the magnitude of CF caused by Zn in soil was
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higher in dry season. In addition, the CF of Zn was decreasing with lateral distance from the centre point of the area.
Figure 4.51: Spatial distribution of CF of Zn in (a) dry season and (b) rainy season.
4.7.1.4 Cadmium
Figure 4.52 (a) and Figure 4.52 (b) show the distribution pattern of CF of Cd along the waste disposal site for dry and rainy, respectively. The magnitude of the CF of Cd for soil sample from central point (approximately 0 m) ranges from 32.53 to 34.99, while, for soil sample from farthest point (390m from central point) ranges from 12.77 to 15.24 for dry season.
Besides, CF of the same metal ranges from 17.29 to 15.66 for soil sample from near to centre (approximately 30 m) and 6.23 to 7.61 for soil sample from farthest point (315m from central point) in rainy season. Outcome of the CF distribution depicted that the magnitude of CF decreases in relation to the increasing of soil sampling distances from approximately the central point of waste disposal site. Comparing seasonal CF of Cd, dry seasonal Cd concentration was high.
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Figure 4.52: Spatial distribution of CF of Cd in (a) dry season and (b) rainy season.
4.7.1.5 Arsenic
The spatial distribution of contamination factor (CF) for the metal elements of As in soil for dry and rainy season is represented in Figure 4.53 (a) and Figure 4.53 (b), respectively.
During dry season, the value of the CF of As for soil sample from central point (approximately 0 m) ranges from 4.42 to 4.56, while, for soil sample from farthest point (390 m from central point) ranges from 0.86 to 1.3. Besides, during rainy season the CF of the same metal ranges from 1.88 to 2.04 for soil sample from near to centre (approximately 30 m) and 0.48 to 0.66 for soil sample from farthest point (315 m from central point). Thus, it is clear that the CF of As was higher in soil of the centre and decreased gradually to outer side soil of the disposal site. Figure also shows the range of CF caused by As was slightly greater in dry season than rainy season.
Figure 4.53: Spatial distribution of CF of As in (a) dry season and (b) rainy season.
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Figure 4.54 (a) and Figure 4.54 (b) illustrate the distribution map of CF for Hg in soil for the durations of dry season and rainy season, respectively. The magnitude of the CF of Hg for soil sample from central point (approximately 0 m) ranges from 0.837 to 0.916, while, for soil sample from farthest point (390 m from central point) ranges from 0.199 to 0.279 for dry season. In addition, CF of the same metal ranges from 0.37 to 0.4 for soil sample from near to centre (approximately 30 m) and 0.09 to 0.12 for soil sample from farthest point (315 m from central point) in rainy season. The distribution pattern of CF in dry season was irregular where in rainy season pattern shows uniform distribution along the area. From the figure it can be said that the high level of CF caused by Hg was present in the soil of central point where it was decreased along the lateral distance. Moreover, Dry season shows the high range of CF (Hg) values.
Figure 4.54: Spatial distribution of CF of Hg in (a) dry season and (b) rainy season.
4.7.1.7 Titanium
The spatial distribution of CF of Ti in the sample soil for dry and rainy season is presented in Figure 4.55 (a) and Figure 4.55 (b), respectively. The extent of the CF of Ti for soil sample from central point (approximately 0 m) ranges from 0.315 to 0.34, while, for soil sample from farthest point (390 m from central point) ranges from 0.112 to 0.137 for dry season.
Besides, CF of the same metal ranges from 0.231 to 0.253 for soil sample from near to centre (approximately 30 m) and 0.043 to 0. 066 for soil sample from farthest point (315 m from central point) in rainy season. The distribution patterns tell that CF of metal is larger values in dry season than rainy season. Though the two seasonal distribution patterns does not cover
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the same geometric area, but it is clear from the figure that CF got decrease along increasing distance from the centre point of the waste disposal site.
Figure 4.55: Spatial distribution of CF of Ti in (a) dry season and (b) rainy season.
4.7.1.8 Antimony
Figure 4.56 (a) and Figure 4.56 (b) show the distribution pattern of CF for the metal elements of Sb in soil along the sampling site during dry and rainy season, respectively. The magnitude of the CF of Sb for soil sample from central point (approximately 0 m) ranges from 57.09 to 62.39, while, for soil sample from farthest point (390 m from central point) ranges from 14.6 to 19.91 for dry season. Besides, CF of the same metal ranges from 27.75 to 30.59 for soil sample from near to centre (approximately 30 m) and 4.91 to 7.79 for soil sample from farthest point (315 m from central point) in rainy season. Figure of distribution reveals that the CF of Sb in soil collected from the central point of the waste disposal site showed higher magnitude than the others. Mainly, along the distances the CF of Sb decreased and during dry season the ranges was higher than rainy season.
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Figure 4.56: Spatial distribution of CF of Sb in (a) dry season and (b) rainy season.
From the above articles, it is sure that all the metal elements considered in the distribution study of CF had a greater magnitude in the soil of the studied waste disposal site during dry season than rainy season. In case of most of the elements considered here, the distribution pattern for CF was quite uniform in both seasons. Though the two seasonal CF distribution patterns for different metals do not cover the same geometric area, but it is clear that the range of magnitude was decrease along increasing distance from the centre point of the waste disposal site. This reduction of this index was caused by the effect of leaching by infiltrating water. Besides, during heavy rainfall, soluble metal content get diluted and runoff from the dumpsite spreads to the surrounding soil.