Heavy metal levels, physicochemical properties and microbial diversity of soil matrix from university solid waste collection sites in Benin City, Nigeria

Abstract

This study was carried out to assess the microbial, physicochemical and heavy metal characteristics of soil samples from five different waste collection sites within the University of Benin, Benin City and evaluated using standard analytical and classical microbiological methods. The heavy metal concentration includes Zn (4.45±0.00 - 5.76±0.02 mg g^−l); Cd (1.59±0.00 - 2.54±0.00 mg g^−l); and Fe (1.02±0.02 - 1.07±0.00 mg g^−l). The physicochemical properties include pH (4.91±0.01 - 5.82±0.04); TOC (6.49±0.01 - 7.65±0.02 %); NO₂ − (29.32±0.07 - 32.81±0.11 mg g^−l); and SO₄ ²⁻ (47.30±0.12 - 63.25±0.04 mg g^−l). The mean of culturable heterotrophic and coliform bacteria ranged from 4.03×10⁷ ± 0.35 - 4.51×10⁸ ± 0.12 CFU/g and 1.02×10⁴ ± 0.12 - 3.10×10⁵ ± 0.02 CFU/g respectively. At p-value < 0.01 level EC significantly correlates total heterotrophic bacteria (r= 0.971); coliform bacteria significantly correlate NO₃ − (r= 0.989); while clay significantly but negatively correlates coliform bacteria (r= -0.989). Some of the bacteria isolated and identified from the waste collection sites include Klebsiella oxytoca, Enterobacter aerogenes, Staphylococcus aureus, Pseudomonas putida, and Bacillus macerans. Findings from this study reveal that the municipal solid waste on the collection sites has impacts on the indicator variables of the resident soil as well as serving as breeding sites for pathogenic organisms.

Keywords: solid waste, environmental hazard, soil quality, pathogens