Abstract
The purpose of this study is to determine the implications for soil conservation of heavy metal concentrations in bitumen-polluted soils. Bitumen-derived heavy metals pose a serious threat to the environment by contaminating soil and harming plants, animals, and ecosystems. The study was carried out at Ode-Irele in Ondo State of Nigeria where there were seepages of bitumen as well as exploratory activities. Composite samples of soils in bitumen seepages and exploratory sites were collected to a depth of 15cm and that of the control was obtained at Ebute-Irele. Heavy metals in soils – Mn, Fe, Cu, Zn, Pb, Cr, Cd, Ni, V, and As were determined using atomic absorption spectrometry. Data were analyzed using descriptive statistics and t-tests of unpaired samples. Results showed that Fe and V were more concentrated statistically in exploratory soil than in control, while only Fe was significantly concentrated in seepage soil than in control soil. Mn (805.00 ± 136.30 mg/kg), Cu (140.00 ± 73.50 mg/kg, 251.00 ± 21.21 mg/kg), and Zn (215.00 ± 105.48 mg/kg, 290 ± 56.57 mg/kg) respectively had statistically lower concentrations in both seepage and exploratory soils than control soil. Mn (805.00 ± 136.30 mg/kg, 870 ± 198.00 mg/kg), Fe (992.50 ± 115.30 mg/kg, 1110.00 ± 141.40 mg/kg), Pb (8.0 ± 3.00 mg/kg, 290 ± 56.60 mg/kg), and As (4.80 ± 1.30 mg/kg, 5.00 ± 0.00 mg/kg) are respectively common to soils where there were bitumen seepages and where exploratory activities have taken place with higher concentrations than corresponding values in bitumen. The values of Mn (805.00 ± 136.30 mg/kg), Cu (140.00 ± 73.50 mg/kg, 251.00 ± 21.21 mg/kg), Zn (215.00 ± 105.48 mg/kg, 290 ± 56.57 mg/kg), Pb (8.0 ± 3.00 mg/kg, 290 ± 56.60 mg/kg), Ni (13.00 ± 8.70mg/kg, 15.00 ± 7.10mg/kg), As (4.80 ± 1.30 mg/kg, 5.00 ± 0.00 mg/kg), Cr (9.75 ± 0.50 mg/kg, ± 10.00 ± 0.00 mg/kg) and Cd (2.50 ± 1.00 mg/kg, 3.50 ± 0.71 mg/kg) respectively in both seepage and exploratory soils exceed FEPA (1991) guidelines. Higher concentrations of heavy metals in bitumen-polluted soil should be continuously monitored during bitumen mining as they may represent significant environmental risks to soil conservation.

Key words: Bitumen, Conservation, Heavy metal, Pollution, Soil