Isolation Characterization and antimicrobial Effect of Humic Acid obtained from Soil at Diffrent Sites in Ile-Ife
This study characterized and determined the heavy metal load and antimicrobial activity of humic acid (HA) isolated from different soils in Ile– Ife. It also examined the plant anti- viral activity of the isolated HAs. This was with a view to assessing the prospect of the usage of humic acid as antimicrobial and plant growth agent. Soil samples were collected from three different areas (hospital waste dumpsite of the Obafemi Awolowo University (OAU) Teaching Hospital, municipal waste dumpsite of Moremi Hall of Residence, OAU and an automobile workshop, where spent oil has been deposited overtime in Ile-Ife. Humic acid was extracted by treatment of the soil samples with dilute NaOH (1:10) in 250 ml conical flasks. The Infra Red Spectroscopy of isolated HA was determined using a Perkin Elmer Fourier Transform Infra Red (FT - IR) Spectrometer. The digests from soil samples were analyzed for the selected heavy metals (Pb, Cu, Cr and Fe) using Atomic Absorption Spectrophotometry. The antimicrobial activity of the isolates was tested against clinical isolates of some aerobic bacteria using agar well diffusion method. A standard antibiotic (streptomycin) was used as positive reference standard. Clinical isolates of the following microorganisms were used for the study: Escherichia coli, Proteus vulgaris, Klebsiella pneumoniae, Bacillus polymyxa, Bacillus cereus, Staphylococcus aureus, Clostridium sporogenes, Corynebacterium pyogenes, Bacillus stearothermophilus, Enterococcus faecalis, Micrococcus luteus, Pseudomonas fluorescence and Bacillus subtilis. These microorganisms were obtained from the laboratory stock of the Department of Microbiology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. The antiviral activity of the isolates was evaluated using two cowpea varieties (Ife Brown and TVu 76) as test plants in a Randomized Complete Block Design with six treatments which included the control experiment. The results from the Fourier Transformed Infrared spectra of HA extracted from soils in Ile-Ife were found to be similar. The HA spectra showed strong hydrogen bonded O – H/ N – H stretching vibration at 3760.00 cm-1, Dimeric O- H stretching vibration at 3453.00 cm-1. A low intensity absorption indicative of an olefinic (C = C) or aromatic C = C bond was seen at 1639.57 cm-1while an absorption at 1401.55 cm-1 indicative of phenols was also observed. Absorption at 1113.79 cm-1 and 1031.08 cm-1indicative of C – O stretch of aliphatic or aromatic alcohol, cyclic/ acyclic esters, ethers or carboxylic acid. The HA from municipal waste dumpsite had less carbonyl content compared to that from hospital waste dumpsite and automobile workshop. The values of the heavy metals considered (Pb, Cu, Cr and Fe) for the soils and HAs from different sites are within the safe limit of the European commission except for Iron (Fe) with values higher than 1500 mg/kg which is the European commission limit. Results of the antimicrobial activity showed that HA displayed very good antimicrobial activity against E. coli, P. vulgaris, K. pneumoniae, B. polymyxa, B. cereus, S. aureus, C. sporogenes, C. pyogenes, E. faecalis, P. fluorescence and B. subtilis compared to the standard drug (streptomycin) but had no effect on B. stearothermophilus and M. luteus. For plant anti- viral activity, the treatments had significant effect on the yield parameters for the two cowpea varieties (Ife Brown and Tvu 76). The study concluded that the isolated humic acids exhibited good broad spectrum antimicrobial activity and that humic acid was a multifunctional compound.