HEAVY METALS CONTAMINATION OF SOILS IN AUTO MECHANIC WORKSHOP IN BENIN CITY, EDO STATE

ABSTRACT

The study was carried out to investigate contamination of soils by heavy metals in three auto mechanic workshops situated in three different local government areas within Benin City metropolis; namely, Oluku in Ovia North East, Uselu in Egor, and wire Road in Oredo Local Government Area of Edo State, Nigeria. Three auguring points were randomly selected in each of the workshops and Soil samples were collected at two different depths (0-15cm and 15-30cm) with three replicates each. Also, soil samples were collected at three different spots ,100 metres away from each of the workshops to act as control experiment. The results showed that the soils from different automobile mechanic workshops had a basic pH.  The analysis of soil samples from selected auto mechanic workshops reveals significant concerns regarding heavy metal contamination. In particular, lead (Pb) concentrations in the topsoil (0–15 cm) 0.008mg/kg, 0.012mg/kg 0.018mg/kg exceed the critical threshold of 0.005 mg/kg, indicating toxic accumulation likely resulting from the indiscriminate disposal of used lubricating oil. Moreover, the observed increase in Pb levels with depth suggests potential leaching into deeper soil layers, which could eventually threaten groundwater quality. Selenium (Se) levels across all sampling sites remain below the deficiency threshold of 0.15 mg/kg, which could compromise soil fertility despite avoiding toxicity. Conversely, chromium (Cr) and cobalt (Co) concentrations are within safe limits, with chromium (Cr) well below contamination thresholds and Co exhibiting minimal mobility. Mitigating strategies to reduce automobile workshops from causing reduced soil fertility includes; setting up automobile mechanic workshop in far areas where agriculture is not practiced and also remediation strategies.