Abstract

Crude oil spillage is one major means of environmental pollution in oil and gas exploration and production. Since 1976, about 5334 cases of crude oil spillage releasing an estimated 2.8 million barrels of oil into the land, swamps, estuaries and coastal waters have been reported in Nigeria (Odiete, 1999). Heavy metals in crude oil are of varying concentration that can affect the concentration of the naturally occurring heavy metals in the soil after a spill. This situation brings about an artificial imbalance in the heavy metals concentration in the soil.

This paper studies the after effect of crude oil spillage in two locations. Data were collected two and six months after the spillage and analyzed to determine the concentration levels of some associated heavy metals in the soil. Soil samples from the polluted and unpolluted areas were collected from the topsoil and subsoil and analyzed for these associated heavy metals. The results showed that there were increased concentrations of Zinc (Zn), Manganese (Mn), Lead (Pb) and Iron (Fe) two and six months after the crude oil spillage but Nickel (Ni) did not show any increased concentration. Copper (Cu) however, showed an increased concentration in the polluted area than the unpolluted area after two months of the spill but no increase in concentration after six months.

It is the devastating consequences of crude oil spillage on arable farmland with its eventual hazards to the environment that has necessitated this study.

Introduction

Crude oil spillage is one major means of environmental pollution in oil and gas producing areas. It has far reaching effects in the soil and water where it distorts their structures and affects the biota. Since 1976, about 5334 case of crude oil spillage releasing an estimated 2.8 million barrels of oil into the land, swamps, estuaries and coastal waters have been reported in Nigeria (Odiete, 1999). It is noteworthy that the devastating consequences of spill of crude oil with its eventual hazards to both aerial and terrestrial environs is tantamount to irreversible chain effect on both bio-diversity and human safety (Akpofure et al, 2000).

Heavy metals can be defined as trace metals with densities greater than 5 g/cm. The heavy metals in the crude oil find their way into the environment when there is spillage. According to Smith et al (1999), the heavy metals in the crude oil are of varying concentration that can affect the concentration of the naturally occurring heavy metals in the soil after crude oil spillage. This situation brings about an imbalance in the heavy metals concentration in the soil polluted by crude oil spillage. When crude oil is disposed to the environment, the heavy metals accumulate in the sediments and biota if it was disposed into the water. According to Harold and Jerry (1976), high discharge of oil into the water results in an exponential decrease of the heavy metals over time with no significant increase in the sediment. When the crude oil is discharged on land, the oil being immiscible with water migrates to the water table causing the heavy metals to be deposited at varying concentrations on the soil layers. According to Osuji and Onojake (2004), heavy metals in crude oil show significant mobility in polluted soil. They reported that crude oil polluted soil show slight acidity, high moisture content and high total organic content after six months of the pollution.

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