Ecological Risk and Bacteriological Assessment of Top Soil Samples from Lairage Locations in Benin Metropolis, Nigeria

Abstract

This study assessed the ecological risk and bacteriological qualities of soil
samples from lairage locations in Benin metropolis. Standard analytical
procedures and pour plate technique were employed in the determination of
the physicochemical, heavy metal and heterotrophic microbial flora of the
topsoils. Ecological risk was assessed adopting standard mathematical
equations. The pH values range from 6.04 – 7.73, electrical conductivity
range from 931 – 3100 (µS/cm), percentage organic carbon mean values were
7.29 % -14.6 % and ammonium nitrogen values ranged from 5.21 mg/kg –
24.5 mg/kg. Iron had the highest concentration range from 322.3 – 573.2 -
573.2 mg/kg. Manganese levels ranged from 2.92 - 29.6 mg/kg; range
concentrations for copper, chromium and lead were 0.28 -3.10 mg/kg, 0.19 –
1.50 mg/kg and 0.11-2.18 mg/kg respectively. Pollution load index results of
this studied soil samples were greater than 100, thus indicating that heavy
metal pollution require immediate remediation action. Potential ecological
risk index for individual heavy metals showed slight degree of ecological risk
as values were less <40, with lead having ecological risk value of 10.62. The
total heterotrophic bacterial and fungal counts range from 2.3 – 16.1 (x 104
cfu/g) and 0.6 – 3.6 (x 104
cfu/g) respectively. The predominant microbial
isolates were species of Micrococcus, Bacillus, Pseudomonas, Escherichia,
Staphylococcus, Klebsiella and Enterobacter Aspergillus, Mucor, Penicillium
and Trichoderma. This study hereby strengthens the concern that
administrators and owners of lairages should monitor and manage heavy
metals pollution.