Soil physicochemical and hydraulic properties of petroleum-derived and vegetable oil-contaminated Haplic Lixisol and Rhodic Nitisol in southwest Nigeria.

Various daily human activities can result in the release of pollutants of different chemical constituents and specific gravities into natural soils. Pollution of natural soils is a recurring occurrence in the environment and it contributes greatly to the alteration of soils properties. The results of an assessment of the effects of selected petroleum-derived and vegetable oils on soil physicochemical and hydraulic properties are presented in this work. Topsoil samples at a depth of 0-20 cm of the same textural class were collected from the order Lixisols and Nitisol within Ogun State, southwest Nigeria. Surface soil samples were collected and treated with petrol, diesel and palm oil at two different volumes (50 and 100 ml). Investigated soil properties include particle size distribution, soil pH, bulk density (BD), total porosity (TP), saturated hydraulic conductivity (Ksat), available water capacity (AWC), total carbon (TC), total nitrogen (TN), organic matter (OM) content, cation exchange capacity (CEC), potassium, sodium, and soil resistivity. Analysis of variance and Pearson's correlation were used to study the variations of the relationship of analyzed soil properties under different soil types and treatments. The regression analysis shows that all the generated models for predicting Ksat values under different soil treatments had R2 values ranging from 0.999 to 1.000. Results showed that treatment with either petroleum-derived or lipids has no effects on soil pH and textural class. Results further revealed that palm oil contamination at 50 ml recorded least values of Ksat in the two soil types. In all cases, BD and Ksat of the contaminated soils of the two sampling locations were reduced compared with their control values. Correlation coefficient showed expected strong negative correlation between TP and BD as well as between any two of organic parameters (TC, TN, and OM) and soil resistivity, TC, and TN at 1% level in both soil types. Two-way ANOVA showed that there were significant differences at 5% level between the two locations with respects to BD, TP, and CEC while significant differences in Ksat, pH, TC, TN, and OM occur between soils from the two locations under various treatments at 5% level.