ENVIRONMENTAL ASSESSMENT OF HEAVY METAL CONTAMINATION AND ECOLOGICAL RISK IN SOILS AROUND PETROL STATIONS IN ONITSHA, SOUTHEASTERN NIGERIA
DOI:
https://doi.org/10.58885/ijees.v11i1.94.ojeKeywords:
Petrol station, heavy metals, soil contamination, contamination factor, pollution load index, ecological risk, Onitsha.Abstract
Core soil samples were collected from ten selected petrol stations in Onitsha, southeastern Nigeria, with an undeveloped control site at Awka used for background comparison. Particle-size distribution, pH, organic matter, cation exchange capacity (CEC), and concentrations of Pb, Cu, Zn, Cr, Ni, Co, Mo, Cd, Mn and Si were determined using standard laboratory procedures and atomic absorption spectrophotometry. The soils were predominantly sandy and acidic (pH 5.23–5.82), with CEC of 0.171–0.341 Cmol kg−1 and organic matter of 6.592–13.67%. Mean±sd concentrations of Pb, Cu, Zn, Cr, Cd, Ni, Co, Mo, Mn and Si were 1.497±0.232, 0.742±0.228, 3.415±2.706, 2.498±0.273, 0.075±0.053, 1.458±0.324, 0.247±0.097, 0.255±0.071, 6.148±1.068, and 9.291±0.77 mg kg−1, respectively. Although most mean concentrations were below generic soil guideline values, all investigated metals except Mo and Si showed enrichment relative to the local control soil, indicating a measurable anthropogenic contribution. Contamination factors calculated from the control-site background were generally low to moderate, with elevated factors particularly for Ni, Cr, Co and Pb. Pollution Load Index values calculated from Pb, Cu, Zn, Cr, Cd, Ni and Co ranged from 2.42 to 6.07, confirming pollution at all petrol-station sites. The potential ecological risk assessment identified Cd and Ni as the principal contributors to ecological risk, with overall risk ranging from moderate to considerable among the sites. Geoaccumulation indices further indicated strong enrichment of Ni relative to the local background concentration. The results indicate that recurrent fuel handling, spills, traffic-related inputs and facility-associated activities contribute to soil metal enrichment in Onitsha. Regular monitoring, spill prevention, proper storage and handling of petroleum products, and remediation of affected soils are recommended.
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