Long-Term Effects of Crude Oil Spillage on Selected Physicochemical Properties Including Heavy Metal Contents of Sandy Tropical Soil

Crude oil spillage effects on the environment often wane with time, making late remediation of affected soils look irrelevant. Physicochemical quality of a sandy soil under 9-year-old spillage was compared with that of adjacent unaffected site in southern Nigeria. Soil bulk density and equilibrated water content were higher in affected than unaffected site, but permeability did not change. The spillage increased soil pH, organic carbon, total nitrogen and available phosphorus by about 7%, 1700%, 133% and - 16%, respectively. It lowered divalent exchangeable bases/acidity but raised base saturation. It increased total petroleum hydrocarbon (PHC_t) and micronutrients/heavy metals (Fe, Mn, Zn, Cd and Pb), all of which were below their critical limits in soils by regulatory bodies. Soil pH, organic carbon and PHC_t correlated positively with all five micronutrients/heavy metals; total nitrogen did so with Zn and Pb. Nine-year period may be insufficient for spillage effects in sandy soils to cease to be evident. Such effects for PHC_t and heavy metals, however, are deemed tolerable for ecological safety.