ABSTRACT
Soil characterization and levels of heavy metals in two different soil depths (0 - 15 cm and 15 - 30 cm depth) and groundwater of automobile mechanic workshop soil at unit areas of Yola metropolis, Nigeria were carried out between September and December, 2014.The physicochemical parameters of the soil such as pH, particle size, cation exchange capacity (CEC), organic matter (OM), electrical conductivity, phosphates and sulphates were determined. The soil samples were subjected to sequential extraction to ascertain the mobility of the metals in the soils. Statistical analysis on the data obtained was carried out using One- way ANOVA. The results indicated that the soils at the experimental and control sites were a mixture of sandy loam, clay and slightly acidic. The %OM and CEC for the experimental soils were higher than the soils of the Nigerian Savanna. The concentrations of the studied metals (Zn-64.00mg/kg, Pb-45.22mg/kg, Cd2.84mg/kg, Fe-151.58mg/kg and Ni-16.06mg/kg) in the soils from experimental sites were higher than the corresponding values from the control site (Zn-5.75mg/kg, Pb2.07mg/kg, Cd-1.90mg/kg, Fe-36.65mg/kg and Ni-2.1mg/kg), and also, higher than the recommended limits given by the World Health Organization (WHO). The soil samples showed remarkably high levels of all the metals (Ni, Fe, Zn and Pb) above background concentrations with most of them decreasing with decrease in soil depth. The distribution was in the following order Fe> Zn> Pb > Ni > Cd. Across the sampling locations and profiles, Fe and Cd gave the highest (154.58 mg/kg) and least (2.54 mg/kg) values respectively. Pollution load index (PLI) and geoaccumulation index(Igeo) revealed overall high and moderate contamination respectively while the enrichment factors (EFs) for Zn and Ni were severe. The inter-elemental relationship revealed an identical source of elements in the soils of the studied areas. The levels of metal in groundwater within the mechanic workshops at different distances of 20m and 30m away from each location were determined. The results indicated that, the levels of metal in groundwater were higher in 20m than 30m away from the mechanic workshops. At 20m, Zn was the highest in Demsa phase1 (14.03 mg/kg) and least at Girei (1.16 mg/kg ), Pb was highest in Demsa phase1(1.96mg/kg ) and least in Gombi and Ganye (1.56 mg/kg ), Cd was the highest in Demsa Phase1(0.21 mg/kg ) and least in Demsa Phase2(0.15mg/kg ), Fe was the highest in Demsa Phase1 (1.73mg/kg ) and least in Gombi and Ganye (0.83mg/kg ) and Ni was the highest in 200Unit (45.55 mg/kg) and least in Ganye (0.07 mg/kg ). While at 30m, Zn was the highest in Demsa Phase2 (6.34mg/kg) and least in Girei (0.16mg/kg ), Pb was highest in 200Unit and Ganye (1.56mg/kg ) and least in Demsa Phase1 (1.25mg/kg ),Cd was highest in 200Unit and Ganye (0.15 mg/kg) and least in Demsa Phase1, Demsa Phase2 and Girei(0.13mg/kg ), Fe was highest in 200Unit (1.54mg/kg ) and least in
Gombi and Ganye (0.64 mg/kg ) and Ni was highest in Demsa Phase1&2 (0.09 mg/kg ) and least in Girei (0.01mg/kg).The accuracy of the results has been cheeked using the standard reference material; SRM (PACS-2). The mechanic workshop soils represent potential sources of heavy metal pollution to the environment. The elevated levels of heavy metals in these soil profiles constitute a serious threat to humans live, surface and groundwater.
CHAPTER ONE
1.0 INTRODUCTION
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.
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.
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.
i. Determination of some physicochemical parameters, such as pH, clay, silt, sand, Electrical conductivity, organic carbon, Cation Exchange Capacity, PO43- and SO42- in the soil sample.
ii. Determination of the concentration of Cd, Fe, Ni, Pb and Zn in the soil sample and groundwater located within the vicinity of these automobile mechanic workshops.
iii undertake speciation studies to determine the mobility of the above heavy metals in the vicinity automobile mechanic workshops.
Because of the pollution associated with heavy metal at elevated concentration to humans lives, surface water and underground water in the environment. There is need to ascertain the levels of the heavy metal in this environment.
The work is intended to give a base line data for future investigation of activities leading to temporary changes, in concentrations of heavy metals in the vicinity of automobile mechanic workshops in the areas studied (Yola). Since no known work of this nature has yet been done in this town.
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