CHAPTER ONE1.0 INTRODUCTIONSoil contamination is one of the major environmental problems facing the world today.Contamination of soil by hydrocarbons (mostly petroleum hydrocarbons) is becomingprevalent worldwide (Njoku et al., 2008). This is probably due to heavy dependence onpetroleum as a major source of energy throughout the world, rapid industrialization,population growth and complete disregard for the environmental health. In Nigeria, oilpollution problems have been prevalent since the commencement of oil exploration anddevelopment of the petroleum industry (Okohet al., 2001). Release of hydrocarbons into theenvironment whether accidentally or due to human activities is a main cause of water and soilpollution (Holligeret al., 1997). These hydrocarbon pollutants usually cause disruptions ofnatural equilibrium between the living species and their natural environment. Hydrocarboncomponents have been known to belong to the family of carcinogens and neurotoxic organicpollutants (Das and Chandran, 2010). The amount of natural crude oil seepage was estimatedto 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 extensivedamage of body system since accumulation of pollutants in animals and plant tissue maycause death or mutations (Sheetal, 2012). These oil spills can even cause damage to the seaand shoreline organisms (Rodríguez-Martínez,2006). Other sources of contamination includeservice stations, garages, scrap yard, waste treatment plants, saw mills, etc. Hydrocarbonsdiffer 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 aromatichydrocarbons (PAHs), may not be degraded at all. Between 1976 and 1996, a total of 4,647oil spill incidents were recorded in Nigeria which resulted in the spill of approximately 2.31 million barrels of oil into the environment (Kotangora, 1991)and between 1997 and 2001, atotal of 2,097 oil spill cases were also recorded, causing severe damage to soil resources andthe coastal environment (EkpebuandUkpong, 2013). There are several classes of chemicalsthat have been targeted by United States Environmental Agency (USEPA) as prioritypollutants due to their toxic effects on the environment and human health. Thesechemicalsinclude polycyclic aromatic hydrocarbons, penta-chlorophenols, polychlorinatedbiphenyls, 1,1,1- trichloro – 2,2-bis (4-chlorophenyl) ethane, benzene, toluene, ethylbenzene,xylene and trinitrotoluene. Polycyclic aromatichydrocarbons (PAH) are recalcitrant environmental contaminants that aregenerated from the burning of fossil fuels, coal mining, oil drilling and wood burning (Lau etal., 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 thatoccur on the land surface (www.nrcs.usda.gov). The soil is a key component of naturalecosystems because environmental sustainability depends largely on a sustainable soilecosystem (Adriano et al.,1998). When soil is polluted, the ecosystem is altered andagricultural activities are affected. Organic compounds such as crude oil and by-productshave been reported as hazardous to plants (Achubaet al., 2015). They also determine theemergence of seed, plant development and growth (Odejegba and Sadiq ,2002). In Nigeria,most of the terrestrial ecosystem and shorelines in oil-producing communities are importantagricultural land under continuous cultivation. Any contact with crude oil damages the soil inthe agricultural lands, including adverse effects on microorganisms and plants (Onuohaetal.,2003; Kadafa,2012).2 1.2WHAT ARE HYDROCARBONS?Hydrocarbons areany of a class of organic chemical compounds composed only of theelements carbon (C) and hydrogen (H). The carbon atoms join together to form theframework of the compound, and the hydrogen atoms attach to them in many differentconfigurations. Hydrocarbons are the principal constituents of petroleum and naturalgas(www.britannica.com). Hydrocarbon contamination of the air, soil, freshwater (surfacewater and groundwater) especially by PAHs has drawn public concerns because many PAHsare toxic, mutagenic, and carcinogenic. Aromatic hydrocarbons are considered to be the mostacute toxic component of petroleum products, and are also associated with chronic andcarcinogenic effects (Andersonet al., 1974). Aromatics are often distinguished by the numberof rings they possess, which may range from
