One of the unintended impacts of crude oil exploration is the
pollution of agricultural land and aquatic resources when there is
accidental oil spillage. The environmental effect of this has resulted
in untold hardship to communities within oil producing regions all over
the world and has been the main reason for conflicts in the regions.
Nigerian Niger Delta region has been devastated by oil pollution and gas
flaring, and both the government of Nigeria and the multinational oil
producing companies have been searching for solutions for the recovery
of oil polluted soil. Among the various possible methods of recovery of
crude oil contaminated soil, bioremediation is most environmentally
A promising bioremediation method is the use of crops with phytoremediation capabilities. Cowpea (Vigna unguiculata) which
belongs to the family of legumes is one of such crops. In addition to
their nutritional value, legumes can be used in the cleaning up of crude
oil contaminated soils through different mechanisms such as;
biodegradation in the rhizosphere, plant uptake, translocation,
transformation, and phytovolatilization. This research was aimed at
evaluating the phytoremediation capabilities of cowpea towards the
recovery of crude oil contaminated soil in the Niger Delta region of
Five (5) plastic buckets with 1000g of soils were contaminated with
crude oil at different levels; 0 ml, 30 ml and 40 ml. The remaining two
buckets contained 30 ml crude oil + 0.5g Indole acetic acid (IAA) and 40
ml crude oil + 0.5g IAA respectively. The Indole Acetic (IAA) - a
growth hormone was introduced to the contaminated soil to improve
performance. Cowpea was grown in the soil and the germination and height
of the crop were monitored. The presence of heavy metals in the soil
and plant were measured.
Results show that the heights of cowpea plants in the control
experiment were greater than those of plants in 30 ml crude oil + IAA,
while the plants in 30 ml crude oil only being the least. Atomic
absorption spectroscopy analysis of the plant samples indicated cowpea
plants in 40 ml crude oil + IAA to have the highest accumulation of
heavy metals. EDXRF results of the soil samples presented the soil with
40 ml of crude oil to have the highest accumulation of heavy metals.
These results indicate that cowpea has phytoremediation capabilities.
Indole- 3-acetic acid has the potential of facilitating the rate of
phytoremediation of contaminated soil.
Thus, it is concluded that cowpea can be used to clean-up crude oil contaminated farm lands in the Niger Delta, Nigeria.
Bioremediation refers to the use of biological mechanisms to destroy,
transform, or immobilize environmental contaminants so as to protect
potential sensitive receptors. (Bioremediation Discussion Group, 2006).
Two remediation techniques are; Ex situ and In situ remediation techniques. Ex situ remediation techniques involve taking out the soil fromthe subsurface in order to treat it. In situ remediation
techniques encompass leaving the soil in its original place and
bringing the biological mechanisms to the soil. Earlier thermal,
chemical and physical treatment methods have been unsuccessful in
eliminating the pollution problem because those approaches only move the
pollution to a new phase such as air pollution. Bioremediation
technology, which leads to degradation of pollutants, may be a
worthwhile and environmentally beneficial substitute that could produce
an economic profit (Iranzo et al., 2001.)
In Niger Delta, Nigeria, increased petroleum exploration has led to
an unprecedented accidental release of crude oil polluting the land and
water sources of the area. Furthermore, illegal tampering of well heads,
flow lines, pipelines, manifolds and flow stations have added to the
total amount of crude oil entering the environment. With recurrent
reports of oil spillage in Niger Delta, there is a need for a cost
effective method for remediation of crude oil contaminated soil. Crude
oil affects the physicochemical properties of the soil such as
temperature, structure, nutrient status and pH when spilled on land
(Udeh et al., 2013).