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1.1 Background to the Study

The increase in automobile repairs/workshops and their activities in Nigeria are partly due to the ever-increasing demand for personal vehicles, most of which are used “Tokunbo” vehicles. These have contributed remarkably to the problem of soil contamination in most cities. Automobiles used oil (waste) contains oxidation products, sediments, water and metallic particles resulting from machinery wears, used batteries, organic and inorganic chemicals used in oil additives and metals (European Environment Agency, 2007). Soil Percolation of leachates from these materials poses threats to groundwater. Unfortunately, information on the impact of automobile mechanics‟ activities on the ecosystem is still very unavailable. The co-existence of toxic heavy metals and hydrocarbons (HCs) at many of the mechanics contaminated sites all over Nigeria and in other developing countries pose a severe threat to the environment. In fact, the presence of trace elements in soil is increasingly becoming an issue of global concern especially as soil constitutes a crucial component of rural and urban environment (United States Department of Agriculture 2001, Lim, 2008). Heavy metals such as cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn) which are often used as additives in some lubricants and gasoline are non-degradable in the soil. Some of them have been classified as priority pollutants by United State Environmental Protection Agency(United States Department of Agriculture 2001). At the moment, very few technologies, such as soil washing and bioremediation, are available to treat these mixed wastes (Sharma, 2004) The problem of soil and vegetation pollution due to toxic metals in spent oil is cause for concern in most metropolitan cities (Vwioko et al., 2006). These toxic heavy metals entering the ecosystem may lead to bioaccumulation and bio magnifications (Wong et al., 2002). Spent oil soil pollution leads to the build-up of essential and nonessential elements in the soil and eventual translocation in plant tissues (Vwioko et al., 2006). Soil pollution by spent lubricating oil has been reported to cause growth retardation/ reduction in plants and this has been attributed to the presence of heavy metals at toxic concentrations in the soil (Anoliefo and Vwioko, 1995). Due to the ever-increasing population and industrialization, most environments are to some extent polluted. It is also estimated that the contributions of metals from anthropogenic sources in soil is higher than the contribution from natural ones, hence, the repeated evaluation of the contamination status of soils (Nriagu, 1988). Nriagu (1978) reported that we may be experiencing a silent epidemic of environmental metal poisoning from the increasing amounts of metals released into the biosphere. Waste engine oil pollution is responsible for several environmental problems, including disruption of plant water relations having direct toxicity and indirect effects on plant metabolism (Racine, 1994). Edebiri and Nwanokwale (1981) found that metals present in spent lubricating oil are not necessarily the same as those present in unused lubricant. Heavy metals such as vanadium, lead, aluminium, nickel and iron which are low in unused engine oil gave higher concentrations in spent engine oil. Hall (2002) observed that heavy metals, such as copper and Zinc are essential for normal plant growth. There are researches in the Southern part of Nigeria onspent oil pollution of soil and vegetation, but not much has been done on spent oil pollution in the North Central region of the country. Consequently, this work is initiated to study and evaluate soil pollution due to heavy metals in spent lubricating oil in the vicinity of some mechanic workshops in Yola Metropolis of North Central Nigeria.

1.3 Statement of Research problem

Yola is one of the largest towns in the north central part of Nigeria. It has a population of about 196,643 according to the 1996 population Census. Majority of the people engage in town services such as: Motor cycle, taxi and bus driving as their occupation which has led to the existence of many automobile mechanic workshops almost everywhere in Yola town, Also, indiscriminate disposal of their spent oil subjects the soil of thisenvironment to high risk of pollutionwith heavy metals and other harmful substances. Since heavy metals at elevated levels can be dangerous to lives and environment, there is need to check their concentration and mobility in this town. Lack of strict application of environmental protection legislation the need for better control of the pollution situation and absence of basic data about heavy metal pollution from automobile mechanic workshops in the town is the background for the present work. 

1.4 Aim

The aim of this research is to evaluate the level of heavy metals and their mobility in the soil and groundwater of some selected automobile mechanic workshops in Yola metropolis, Nigeria. This aim would be achieved through the following objectives.

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