Bioscience Methods 2017, Vol.8, No.1, 1-18
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seasons of study in all the location which occurred mostly in the dry season. Cadmium showed moderately
contamination in all location across both seasons under BMM scenario. While under BGM scenario, 30%
including LA, LC and LD in wet season showed low contamination. Nickel in wet season for LC showed
considerable contamination. While 40% of other locations comprising both seasons of study showed low
contamination. Under BGM scenario, there was 50% low and moderate contamination comprising of both
seasons.
Chromium showed moderate contamination for LA, LC and LE at both seasons of study under BMM
consideration. Similar trend was observed under BGM consideration for LA and LE of both seasons and LC of
only dry season showed moderate contamination. Under BMM consideration for copper, LB, LC and LD of both
seasons and LA and LC of wet season showed moderate contamination. Whereas in BGM scenario, both seasons
for LE, dry season for LB, LC and LD and wet season for LA showed moderate contamination. Among the
various locations, contaminations indicate the effect of anthropogenic activities on soil heavy metals (Sekabira et
al., 2010; Bhutiani et al., 2017).
Among the 9 heavy metals studied under both seasons in the 5 locations, 59 (representing 65.56%), 2
(representing 2.22%) and 29 (representing 32.22%) showed moderate contamination, considerably contamination
and low contamination respectively under BMM scenario. While in BGM 49 (representing 54.45%), 1
(representing 1.11%) and 40 (representing 44.44%) showed moderate contamination, considerably contamination
and low contamination respectively.
This study showed that contamination level differs depending on heavy metals. This could be due to variation in
anthropogenic activities leading to heavy metal generation, difference source of cassava tuber processed as well as
age of the cassava tuber. Quantity of cassava mill effluents discharged into the soil in the various locations could
also account for variation among the contamination level in each of the location. Runoff resulting from rainfall
during the dry season could also be potential source of variation in the contamination factor.
Based on seasons, wet season has higher contamination (moderate and considerably) level compared to dry season
under BMM scenario. Furthermore, in BGM scenario, dry season has higher contamination (moderate and
considerably) compared to wet season. Comparing the two different background scenarios, fluctuations in the
values could be associated to variation in the mean data. The trend in this study has been reported by Bhutiani et
al. (2017).
The degree of contamination of heavy metals concentration in cassava mill effluent contaminated soil is presented
in Figure 1. Among all the locations and season, there was moderate risk level (8 ≤ CD<16). Though, there was
slight variation between both background levels. This suggests that the soil is being contaminated by the
prevailing activities in each location.
Figure 1 Degree of contamination of heavy metals concentration in cassava mill effluent contaminated soil
Note: CD<8 (Low risk); 8 ≤ CD<16 (Moderate risk); 16 ≤ CF<32 (Considerable); CD>32 (Very high)
BMM- Background Median Mean; BGM- Background Geometric Mean
0
5
10
15
Dry Wet Dry Wet Dry Wet Dry Wet Dry Wet
LA
LB
LC
LD
LE
Locations
BMM
BGM
