THE EFFECT OF CRUDE OIL CONTAMINATED SOIL ON THE PHYSICAL AND BIOCHEMICAL PROPERTIES OF BEANS (PHASEOLUS VULGARIS)

 
Crude oil is a complex mixture of thousands of hydrocarbons and non-hydrocarbon compounds, including heavy metals. Nigeria is an established crude oil exporting nation producing medium and light crude oil, such as bonny light (Amund et al., 1993). Crude oil exportation is the main stay of Nigeria’s economy. Crude oil is a colloidal mixture of different hydrocarbons (90%) and non-hydrocarbon (10%) components (Cadwellaer et al., 1993). Various activities in crude oil exploration, exploitation, storage and transportation lead to spillage of oil to the environment (Agbogidi et al., 2007). Crude oil causes harmful effects on the environment, where it poses a serious threat to organisms and farmland that are linked in a complex food chain that includes humans (Lundstedt et al., 2003). 
The effects of crude oil on the growth and performance of plants have been reported in many studies (Njoku et al., 2008). Crude oil in soil makes the soil condition unsatisfactory for plant growth. It can reduce the level of available plant nutrient in contaminated soils (Jong et al., 1980) and can also raise the levels of certain elements such as iron and zinc to toxic amounts (Udo et al., 1975). Water and oil are usually considered to be immiscible. However, crude oil contains a very small soluble portion referred to as the water soluble fraction (WSF). The soluble constituents are dispersed particulate oil, dissolved hydrocarbons and soluble contaminants such as metallic ions. The components of crude oil that go into solution make up the WSF. The lower the molecular weight of the constituent hydrocarbon of crude oil, the higher is its concentration in the water-soluble fraction (Edema et al., 2012).
Exposure of plants to crude oil and heavy metal poisoning has been reported to produce reactive oxygen species (ROS) and other free radicals which induce oxidative stress and cause lipid peroxidation (Blokhina et al., 1999). Even at an early stage, it can cause a reduction in cell proliferation and growth. Various researchers have reported activation of lipid peroxidation in plants exposed to different pollutants (Chirkova et al., 1998). Increase in superoxide dismutase (SOD) activity has also been reported in oat, wheat and Arabidopsis thaliana in soils contaminated with various pollutants (Alscher et al., 2002). Several plant species have also been shown to have elevated peroxidase activities in response to increased pollutant concentrations (Jouili et al., 2003). Reactive oxygen species is thought to increase cellular damage through the oxidation of several macromolecules such as lipids and proteins (Ortega et al., 2005).
The common dry beans or Phaseolus vulgaris L., is the most important food legume for direct consumption in the world. Among major food crop, it has one of the highest levels of variation in growth habit, seed characteristics (size, shape, colour), maturity, and adaptation. It also has a tremendous variability (> 40,000 varieties). In Africa, beans are grown mainly for subsistence, where the Great Lakes region has the highest per capita consumption in the world. Beans are a nearly “perfect” food. Nutritionally rich, they are also a good source of protein, folic acid, dietary fibre and complex carbohydrates. Beans are also one of the best non-meat sources of iron, providing 23-30% of daily recommended levels (Pachico et al., 1993) from a single serving. Consumption of beans is high mostly because they are a relatively inexpensive food. For the poor of the world, they are a means of keeping malnutrition at bay (WHO. 1992). This research work is geared towards outlining the effect of soil contaminated with crude oil (at various levels) on the biochemical properties and growth rate of beans (phaseolus vulgaris). 

In Niger Delta, oil pollution arising from oil spillages and gas flaring regularly occurs. Therefore, the environment has been destroyed, while the rivers and farmland which the inhabitants rely on for their farming and fishing activities have been rendered unwholesome. This environmental destruction has increased the poverty level of the inhabitants. The prevention of crude oil contamination on soil cannot be overemphasized.  Consequently, the problem of this study is to determine the effect of crude oil pollution on beans germination and growth rate with special reference to the effect on the biochemical characteristics of beans. 

The propose of the study is an attempt to determine the effect the crude oil contaminated soil will have on the growth, relative water content and oxidative status of cultivated beans.   
Aim 
The aim of this study was to clarify whether crude oil contaminated soil will not hinder the growth of beans at physiological levels. 
Objectives of the Study
1.  To investigate effect of crude oil contaminated soil on the growth of cultivated beans.
2.  To investigate the effect of crude oil contaminated soil on the relative water content of the cultivated beans. To investigate the oxidative status of beans planted in crude oil contaminated soil at the molecular level.