Phytoremediation of Crude Oil Contaminated Soil with Carpet Grass (Axonopuscompressus) in the Niger Delta Region of Nigeria

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CHAPTER ONE

1.0 INTRODUCTION

Soil contamination is one of the major environmental problems facing the world today.

Contamination of soil by hydrocarbons (mostly petroleum hydrocarbons) is becoming

prevalent worldwide (Njoku et al., 2008). This is probably due to heavy dependence on

petroleum as a major source of energy throughout the world, rapid industrialization,

population growth and complete disregard for the environmental health. In Nigeria, oil

pollution problems have been prevalent since the commencement of oil exploration and

development of the petroleum industry (Okohet al., 2001). Release of hydrocarbons into the

environment whether accidentally or due to human activities is a main cause of water and soil

pollution (Holligeret al., 1997). These hydrocarbon pollutants usually cause disruptions of

natural equilibrium between the living species and their natural environment. Hydrocarbon

components have been known to belong to the family of carcinogens and neurotoxic organic

pollutants (Das and Chandran, 2010). The amount of natural crude oil seepage was estimated

to be 600000 metric tons per year with a range of uncertainty of 200,000 metric tons per year

(Kvenvolden and Cooper, 2003). Soil contamination with hydrocarbons causes extensive

damage of body system since accumulation of pollutants in animals and plant tissue may

cause death or mutations (Sheetal, 2012). These oil spills can even cause damage to the sea

and shoreline organisms (Rodríguez-Martínez,2006). Other sources of contamination include

service stations, garages, scrap yard, waste treatment plants, saw mills, etc. Hydrocarbons

differ in their susceptibility to microbial attack and can be generally 5 ranked as follows:

linear alkanes > branched alkanes > small aromatics > cyclic alkanes (Rosenberg and Ron,

1996). Some compounds, such as the high molecular weight polycyclic aromatic

hydrocarbons (PAHs), may not be degraded at all. Between 1976 and 1996, a total of 4,647

oil spill incidents were recorded in Nigeria which resulted in the spill of approximately 2.3

million barrels of oil into the environment (Kotangora, 1991)and between 1997 and 2001, a

total of 2,097 oil spill cases were also recorded, causing severe damage to soil resources and

the coastal environment (EkpebuandUkpong, 2013). There are several classes of chemicals

that have been targeted by United States Environmental Agency (USEPA) as priority

pollutants due to their toxic effects on the environment and human health. These

chemicalsinclude polycyclic aromatic hydrocarbons, penta-chlorophenols, polychlorinated

biphenyls, 1,1,1- trichloro – 2,2-bis (4-chlorophenyl) ethane, benzene, toluene, ethylbenzene,

xylene and trinitrotoluene.

Polycyclic aromatichydrocarbons (PAH) are recalcitrant environmental contaminants that are

generated from the burning of fossil fuels, coal mining, oil drilling and wood burning (Lau et

al., 2003; Verdinet al., 2004).

1.1 WHAT IS A SOIL?

Soil is a natural body comprised of solids (minerals and organic matter), liquid and gases that

occur on the land surface (www.nrcs.usda.gov). The soil is a key component of natural

ecosystems because environmental sustainability depends largely on a sustainable soil

ecosystem (Adriano et al.,1998). When soil is polluted, the ecosystem is altered and

agricultural activities are affected. Organic compounds such as crude oil and by-products

have been reported as hazardous to plants (Achubaet al., 2015). They also determine the

emergence of seed, plant development and growth (Odejegba and Sadiq ,2002). In Nigeria,

most of the terrestrial ecosystem and shorelines in oil-producing communities are important

agricultural land under continuous cultivation. Any contact with crude oil damages the soil in

the agricultural lands, including adverse effects on microorganisms and plants (Onuohaet

al.,2003; Kadafa,2012).

1.2WHAT ARE HYDROCARBONS?

Hydrocarbons areany of a class of organic chemical compounds composed only of the

elements carbon (C) and hydrogen (H). The carbon atoms join together to form the

framework of the compound, and the hydrogen atoms attach to them in many different

configurations. Hydrocarbons are the principal constituents of petroleum and natural

gas(www.britannica.com). Hydrocarbon contamination of the air, soil, freshwater (surface

water and groundwater) especially by PAHs has drawn public concerns because many PAHs

are toxic, mutagenic, and carcinogenic. Aromatic hydrocarbons are considered to be the most

acute toxic component of petroleum products, and are also associated with chronic and

carcinogenic effects (Andersonet al., 1974). Aromatics are often distinguished by the number

of rings they possess, which may range from

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Phytoremediation of Crude Oil Contaminated Soil with Carpet Grass (Axonopuscompressus) in the Niger Delta Region of Nigeria

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