ASSESSMENT OF SOIL PHYSICOCHEMICAL PROPERTIES AND TOTAL PETROLEUM HYDROCARBON OF A THREE-DECADE-OLD POLLUTED SITE AT EVBAREKE, BENIN CITY

Abstract

Monitoring of polluted sites require their assessment for effective management and environmental protection. This study assessed the soil properties including heavy metals (Fe, Zn, Mn, Cu, Cr, Pb, Cd and Ni) and total petroleum hydrocarbon (TPH) of a three-decade-old automobile workshop in Benin City. Top soil samples collected from outside the workshop and a control were analyzed using standard laboratory methods and their mean values were compared with critical limits for interpreting soil fertility as well as pollution status. The results showed that the texture of the polluted soil was unchanged but the pH has been modified from strongly to slightly acidic. Relatively slightly higher concentrations of the measured fertility parameters of the polluted site were not substantial for the very low organic C, N and Mg as well as the low for Ca, Na and EC because their ratings were not different from those of the control unlike the high ratings for K and P compared to medium and low in the control, respectively. Concentration of EA of the polluted soil was rated low as the control while effective CEC (cmol/kg) was low for the polluted (6.42) site compared to very low (4.80) of the control. Higher concentrations (mg/kg) of heavy metals in polluted soil were < their DPR target values, except Cd (5.1) which exceeded its limit (0.8). Increased concentration (mg/kg) of TPH from 0.22 to 825 was < its target value of 1,000. Decontamination of Cd from site should be carried out to avoid ill health of workers.