Ecological risk assessment of heavy metals and microbiological diversity of soil samples from some automobile workshops in Benin City, Nigeria

Abstract

The indiscriminate discharge of waste engine oil arising from auto-mechanic workshops is known to cause environmental challenges. This study investigated the pollution status of heavy metals and microbiological diversity of waste engine oil contaminated soils in Benin City. Standard laboratory methods were used in the study. The physicochemical parameters recorded were sandy loam,  pH (6.8 - 7.9), EC (1.9 - 5.4 uS/cm), sulphate (42.51 - 68.45 mg/kg), Nitrate (1.08-2.10mg/kg), Phosphate (2.60- 4.92 mg/kg), Calcium (0.32 -0.64mg/kg), Magnesium (0.17- 0.28mg/kg), Sodium (0.11- 0.14 mg/kg) Potassium (0.10-0.18mg/kg), Zinc (31.92- 68.40mg/kg), Copper (9.21-13.65mg/kg), Chromium (0.23 -0.40mg/kg), Lead (2.40 - 6.20mg/kg), Manganese (32.92-51.70mg/kg), Iron (826.24 — 1012.4mg/kg), Nickel (2.11 — 3.10mg/kg) and Cadmium (1.98-3.10mg/kg). The total heterotrophic bacterial counts of soils samples from location A had the highest, 8.61x10⁴cfu/g while location E had the least, 1.12x10⁴cfu/g. location B had the highest fungal count, 8.04x10³cfu/g while location C had the least, 1.11x10³cfu/g. The bacterial and fungi isolated were Bacillus, Pseudomonas, Micrococcus, Clostridium, Corynebacterium, Penicillium, Fusarium, Aspergillus, Trichoderma and Geotrichum species. The pollution indices indicated iron had the highest contamination factor of 8.88 while Chromium had the least of 0.87. The geo-accumulation index showed that cadmium had the highest of 0.76 while iron had the least. The Quantification of concentration revealed that chromium had the highest of 90.32 while nickel had the least of 57.25. The waste engine oil polluted soil revealed unpolluted to moderately polluted status. This study recommends proper disposal of waste engine oil thereby safeguarding the environment and public health of citizens.