It is noteworthy that, the devastating consequences of the spill of this crude in the Niger Delta region with its eventual hazards on both aerial and terrestrial environs tantamount to an irreversible chain effect on both the bio- diversity and human safety.

2.1 THE ADVERSE EFFECT OF CRUDE OIL SPILLS.

It is our distinct pleasure to highlight briefly the common effects of oil spills in the Niger Delta. We all know that when there is an oil spill on water, spreading immediately takes place. The gaseous and liquid components evaporate. Some get dissolved in water and even oxidize, and yet some undergo bacterial changes and eventually sink to the bottom by gravitational action. The soil is then contaminated with a gross effect upon the terrestrial life. As the evaporation of the volatile lower molecular weight components affect aerial life, so the dissolution of the less volatile components with the resulting emulsified water, affects aquatic life. These factors are considered respectively below:

2.1.1 Spreading

Once Oil is released on water, the process of spreading takes place immediately. This process stands to be the most significant. Some forces influence the lateral spreading of oil on even calm water.

They include:

 [a] Gravitational force which brings about decreasing film thickness, [b] surface tension and inertial forces, the force of gravity is found to be proportional to the film thickness, the gradient thickness and the density difference between the oil and water. The surface tension causes co-efficient of spreading which gives the difference between air/oil and oil/water surface tensions. This force that is independent of the film thickness is the dominant process gotten in the final phase of spreading.

The inertia of the oil body and the oil/water friction, cause retardation on the surface tension. The inertia of a specific oil slick, which is a function of the density and thickness, readily diminishes alongside spreading. Another factor that affects spreading is water temperature.

2.1.2 Evaporation

As evaporation occurs, dissolution also takes place. These two processes are the major ones causing oil degradation after spillage. The type of oil determines the rate of evaporation which varies from almost zero with a residential crude to almost 100% with low boiling point refined products.

2.1.3 Emulsification

This actually is a change of state from oil-in-water dispersion (oil-in-water slick) to water-in-oil emulsion with a resulting thick, sticky mixture containing up to 80% water, and termed chocolate mouse. With oil-in-water dispersion or emulsions such parameters as water, temperature, salinity, pH, presence of surface active agents and suspended particles predominate, as against water-in-oil emulsions.

2.1.4 Petro/Photo Chemical Oxidation

When petroleum or crude oil floats on water surface, it is invariably exposed to attack by atmospheric oxygen, solar radiation, the result of which is degradation to large molecular weight components which subsequently degenerate into water soluble ones. The weight of this attack depends on the weight of oil slick.
 

2.1.5 Bacterial Degradation

Petroleum as well as its refined products is a complex mixture of a wide range of hydrocarbon fractions with sulphur, oxygen and nitrogen compounds. These fractions which include straight or short-branched alkanes, cyclo-alkanes, aromatic hydrocarbons and heterocyclic compounds form a potential carbon and energy sources for microbial activities and hence biodegradable. The micro organism make use of oil in the soil on energy source with such additional nutrients as nitrogen, phosphorus, potassium and an adequate supply of oxygen.

This microbial activity cause crude oil disappearance from the soil after a considerable time.

Accumulation of carbondioxied, water, ammonia and some other intermediates are unavoidable, and the formation of waxy solids by unknown biosynthetic processes are all hazardous, and significantly long lasting.

 2.1.6 Biological Effects Of Oil Slicks In The Aquatic Environment.

Some factors determine the effects of oil on aquatic life. Sometimes a combination of these factors acts simultaneously. These factors are:

The quantity of oil, the quantity of pollution and its duration experienced by the organisms, the state of the oil which might be fresh, weathered or refined products, the season (i.e. the annual cycle of the organism),. The habitat and the natural stresses to which the organism is subjected.

The manner of the effects of these factors are as seen below:

1. Direct lethal toxicity

2. Sub-lethal disruption of physiological and behavioral activities. This leads to death owing to the interference with both feeding and reproduction.

3. Direct coating or painting

4. Entry of hydrocarbons into the food web.

5. Alteration of biological habitats.

It is a case in point that a lot of fish ponds are damaged due to oil slicks. Fish eggs and larvae suffer high rate of mortality, as against the adult fish, which may swim away before it gets hurt.