Abstract
Soil contamination by heavy metals is increasing day by day. In this study, pollution indices which include geo-accumulation index (I-geo), enrichment factor (EF), environmental risk factor (ERF), contamination factor (CF), degree of contamination (CD), contamination/pollution index (C/PI) and pollution load index (PLI) among others were used. The City was divided into four zones; Northwest (NW), Northeast (NE), Southwest (SW) and Southeast (SE). The average total levels of heavy metals in soil samples analyzed in SE, SW, NE, NW and control were 143.1, 118.6, 129.1, 143.3 and 0.85 mg/kg respectively. The levels of Cd in soils from all the zones were greater than the target values. The results of the I-geo ranged between highly polluted to very highly polluted. The CF showed very high level of contamination for all the heavy metals in all the zones. The C/PI values were less than 1 (contamination range) for all the heavy metals in all zones except for Cd which was greater than 1 (pollution range) in all zones. The negative values of ERF recorded for all the metals in all zones implied that the heavy metals analyzed may present potential environmental threat. The PLI values were 331.08, 313.12, 287.54 and 313.86 for NW, NE, SW and SE respectively. This study revealed that automobile workshop is one of the major sources of anthropogenic soil pollution in Benin City and its environs. Keywords : Automobile Workshop, Heavy Metals, Pollution Indices and Soil. DOI: 10.7176/CMR/12-4-04 Publication date: April 30 th 2020
Highlights
Soil contamination is an excess of any element or compound through direct or secondary exposure which causes toxic response from biota and/or humans resulting in unacceptable environmental risks (Vangronsveld et al 2009)
The most common ones are the enrichment factor, environmental risk factor, geoaccumulation index, contamination factor, degree of contamination, pollution load index and contamination/pollution index been widely utilized as a measure of pollution in soil
These results show that the levels of heavy metals in soil samples from the automobile workshops were several orders of magnitude higher than the levels in the control soil sample, suggesting a deleterious impact of activities in automobile workshops on soil quality in Benin City
Summary
Where (X/Fe)soil is the ratio of heavy metal (X) to Fe in the soil from mechanic workshops, and (X/Fe)background is the natural background value of the Metal-Fe ratio. 2.4.4 Contamination Factor Contamination factor (CF) is given by the ratio of the pseudo-total level of the contaminant by the test soil sample to the level in the background sample and indicated on a contamination factor scale of 1-6 viz: CF < 1, low level of contamination, 1≤ CF < 3, moderate level of contamination, 3 < CF < 6, considerable level of contamination, and CF > 6, very high level of contamination (Hakanson, 1980; Anegbe et al 2017). Where (X/Fe)soil is the ratio of heavy metal (X) to Fe in the soil from mechanic workshops, and (X/Fe)background is the natural background value of the Metal-Fe ratio. 3.0 Results and Discussion 3.1 Comparison of average total levels of heavy metals in soil samples of automobile workshops in Benin City with levels in control soil sample Comparison of the pseudo-total levels of heavy metals in contaminated soil with the levels in uncontaminated (control soil) may provide a first-tier indication of “enrichment” of heavy metals in contaminated soil.
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