The effect of crude oil contaminated soil on physical and biochemical properties of beans (Phaseolus vulgaris) was investigated. Thirty polythene pots, each containing 10 kg of surface soil, were randomly placed on a table in the screenhouse in a factorial combination of five treatment levels (0.4%, 0.3%, 0.2%, 0.1% and 0% w/w) of crude oil and were designated P4, P3, P2, P1 and P0respectively. Three seeds of beans per pot were planted. Growth parameters (plant height, stem girth, relative water content (RWC), and soluble protein content (SPC)) and antioxidant indices were determined in the beans over a period of nine weeks after planting (WAP). Results showed that growth of beans planted in contaminated soil was significantly lower (p<0.05) than that of control. Beans planted in the contaminated soil also showed a significant increase (p<0.05) in superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities in leaves when compared with control plants. The results suggest that crude oil contaminated soil hindered availability of water, air and nutrients to beans roots, creating a drought condition which could induce oxidative stress in the plant and consequently retarding growth and yield of beans plant.
1.1 Background of the study
Crude oil is refined to yield products such as gasoline oil, fuel, liquefied gas and grease. Engine oils are used mainly to provide a film between the moving parts of auto machines and engines, which helps to reduce wear and tear and loss of power. It can also prevent corrosion of these auto machine parts. Disposal of spent engine oil into gutters, watercourses, open vacant plots and farmland are common practice among auto machine operators. This practice increases incidence of oil contamination of agricultural soils. Whisman et al. (1974) reported presence of heavy metals such as vanadium, lead, aluminum, nickel and iron in unused lubricating oils, with high values in used ones.
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).
Oil contaminated soils are of environmental concern because they are unsuitable for agricultural and recreational use and are potential sources for surface and ground water contamination.
Environmental pollution is a common hazard in the Niger Delta Region. It is largely due to crude oil explora- tion and exploitation in the area. The activity of man as- sociated with crude oil well drilling on agricultural land has its economic disadvantage on the communities where the crude oil are dug. This environmental pollution re- sulting from the crude oil drilling has put so many food crops at considerable risk. The crude oil contamination has serious damage on the physiological, anatomical and growth performance of plants, soil components and aqua- tic ecosystems. Soil is the most valuable component of the farming ecosystem and environmental sustainability largely depends on proper soil management. Sustainable use of agricultural soil on which plants depend is abso- lutely necessary for agricultural productivity. Soil pollu- tion by crude oil and other petroleum products are pres- ently a menance in Nigeria.
Oil pollution in whatever form is toxic to plant and soil micro-organism. Previous studies by Ogene (2015) had described that oil spills kill agricultural plant or inhibit
the growth performance of the entire vegetation cover. Plants have been described as the first victims of oil spill on land ecosystem. Utibe (2013) reported that oil in soil creates unsatisfactory conditions for plant growth probably due to insufficient aeration of the soil. Oil readily penetrate the pore space of terretrial vegetation following any spill with heavier friction which may block the pores and this subsequently impedes photosynthesis and other physiological processes in plant.
Although, crude oil spills is common in the Niger Delta region, impact of this menance has not been properly studied on the production of vegetables including Phaseolus vulgaris (Beans) is an erect, semi-woody herbeaceous annual crop of the family Malvaceae. It is widely grown in the tropics and highly variable in growth from less than 1m to over 3 m in height. The flowers are yellow and purple and finger- like fruit occurs at the leaf axis. It is ubiquitously cultivated in Nigeria. Though recognised to be capable of germinating on a wide variety of soils, a well drained loamy soil is optimum for its growth. Research report had it that leaves and fruits of Beans plant are eaten fresh and fried as pot-herb. Beans is an important herb in the treatment of Ulcers. The fruits are rich in minerals and vitamins while the stem bark yields fibre. Consequence on these immense domestic and medicinal values of Phaseolus vulgaris (Beans).
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).
1.2 Statement of the problem
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.
1.3 Purpose of the study
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.
1.4 Aim and Objectives of the Study
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
- To investigate effect of crude oil contaminated soil on the growth of cultivated beans.
- 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.
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