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Aims: This study investigated the impact of landfill waste effluents on the population and diversity of soil microorganisms, and a comparative study between landfill soil and effluent-free field soil.

Study Design: A comparative, investigative survey.

Place and Duration of Study: Biotechnology Laboratory, Federal Institute of Industrial Research, Oshodi, Lagos, between August 2015 and February 2016.

Methodology: Soil samples were collected from the surface layers (1-20 cm) of alfisol at the landfill and a field located about 1000 meters from the landfill site. Isolation and characterization of bacteria, actinomycetes and fungi, physical and chemical analysis of the soil samples were performed. One-way analysis of variance (ANOVA) was used for statistical analysis, with level of significance at 0.05.

Results: Mean microbial counts (CFU g-1 dry soil) in landfill soil (Lfs) and field soil (Fs) respectively were: Total bacterial counts 87 ×105 and 72 ×105, coliforms 51×105 and 38 ×105, actinomycetes 44 ×105 and 22 ×105, and fungi 21×105 and 15 ×105, Lfs counts exceeding Fs counts significantly (P < 0.05). The isolates included Proteobacteria (Lfs =16 spp.; Fs=7 spp.), Firmicutes (Lfs =20 spp.; Fs=10 spp.), Actinobacteria (Lfs =10 spp.; Fs=5 spp.), and Fungi (Lfs =15 spp.; Fs=13 spp.), Lfs yielding significantly higher diversity than Fs (P < 0.05). Lfs and Fs respectively contained: moisture (56.8 and 50.9%); pH (6.19 and 6.80); nitrogen (0.99 and 0.42%); phosphorus (553.4 and 371.8 mg/kg); Organic carbon (2.65 and 3.52%); cation exchange capacity (48.14 and 38.8 Cmmol/kg); sand (48.8 and 31.2%); clay (28.8 and 26.0%); silt (22.4 and 57.2%), highlighting differences in chemical and physical properties which support a greater diversity and population of microbes in Lfs more than Fs.

Conclusion: Effluents from landfills enhance the physical and chemical properties of soil, resulting in larger CFU, and greater diversity of all microorganisms. The greater diversity of microbes can be exploited for industry, medicine, agriculture, bioremediation, bio-control and research. The results reveal the importance of citing landfills far from farms, water bodies and residential areas to avoid health hazards in humans, livestock, and adverse effects on plants.