ABSTRACT
Sediment samples from Ikpoba River in Benin City, Edo State were sampled and analysed for heavy metals (Fe, Cu, Zn, Mn, Cd and Pb) using atomic absorption spectrophotometer solar 969 unicam series. Some physio-chemcal properties of the sediment were also determined. The concentration ranges of metals (in mg/kg of dry sediment) measured were in order of Fe (154.00 – 226.1) > Cu (59.64 – 70.20) > Zn (50.98 -66.40) > Mn (39.22 – 57.85) > Pb (5.40 – 22.11)> Cd (3.67 – 16.13). Significant correlation exist at (p<0.01) level and (p<0.05) level between some soil properties and the studies metals. Significant correlation also exist at (p<0.01) and (p0.05) level between the studied metals. The concentration of Fe, Cu, Mn and Cd exceed sediment guideline limit while those of Zn and Pb were below guideline limit. 
CHAPTER ONE
INTRODUCTION
Sediment is the loose sand, silt and other soil particlesthat settle at the bottom of the body of water (USEPA, 2002). It can come from soil erosion or from decomposition of plants and animals. Wind, water andice help to carry these particles to rivers, lakes andstreams.Sediments near urban areas commonly contain high levels of contaminants (Lambersonet al., 1992; Cook and Wells1996) which constitute a majorenvironmental problem faced by many anthropogenically impacted aquatic environments (Magalhaeset al., 2007).Sediments in rivers do not only play important roles atinfluencing the pollution, they also record the history oftheir pollution. Sediments act as both carrier and sourcesof contaminants in aquatic environment (Shuhaimi,2008).Contamination of sediments with heavy metals may lead to serious environmental problem(Loizidouet al., 1992). Heavy metals may adsorb ontosediments or be accumulated by the benthic organisms;their bioavailability and toxicity depend upon the variousforms and amount bound to the sediment matrices(Chukwujinduet al., 2007). Additionally, pollutantsreleased to surface water from industrial and municipaldischarges, atmospheric deposition and run off fromagricultural, urban and mining areas can accumulate toharmful levels in sediments (Chukwujinduet al., 2007)

Heavy metals are classified as metallic elements that have relatively high atomic weight. They are natural components of the earth crust and they cannot be degraded or destroyed (Lentech, 2011). They have specific gravity greater than 4.0 that is, at least 5 times that of water.Heavy metals exist in water, in colloidal, particulate anddissolved forms (Adepoju-Bello et al., 2009).Their occurrence in water bodies are either of natural origin eroded,minerals within sediments, leaching of ore deposits and volcanism-extruded products or of anthropogenic origin(solid waste disposal, industrial or domestic effluents, harbour channel dredging) (Marcovecchioet al., 2007).However, heavy metals are either essential or non- essential. Although heavy metalssuch as cobalt, copper, iron, manganese, molybdenon and zinc are needed at low levels as catalyst for enzyme activities (Adepoju-Bello et al., 2009),Excess exposure tothese essential metals can however, be toxic.Water has unique chemical properties due to its polarity and hydrogen bond which makes it able to dissolve, absorb, adsorb or suspend many different compounds (WHO, 2007). Thus, in nature, water is not pure as it acquires contaminants from its surrounding and those arising from humans and animals as well as other biological activities (Mendie, 2005).

Heavy metals can cause serious health effects with varied symptoms depending on the nature and quantity of the metal ingested (Adepoju-Bello and Alabi, 2005). The most common heavy metals that humans are exposed to are aluminium, arsenic, cadmium, lead and mercury. Aluminium has been associated with Alzheimer’s and Parkinson’s disease, senility and presenile dementia. Arsenic exposure can cause among other illnesses or symptoms, cancer, abdominal pain and skin lesions. Cadmium exposure produces kidney damage and hypertension. Lead is a cumulative poison and a possible human carcinogen (Bakare-Odunola, 2005). For mercury, toxicity results in mental disturbance and impairment of speech, hearing, vision and movement (Hammer and Hammer, 2004). In addition, lead and mercury may cause the development of autoimmunity in which a person’s immune system attacks its own cells. This can lead to joint diseases and ailment of the kidneys and circulatory system and neurons. At higher concentrations, lead and mercury can cause irreversible brain damage. 

In view of growing concern over the use of Ikpoba River by resident along the river banks for drinking,cooking, cultivation of horticultural crops and fishing, this study was undertaken specifically to ascertain the concentrations of Iron (Fe), Copper (Cu), Zinc (Zn) Manganese (Mn), Cadmium (Cd), and Lead (Pb) in sediment of Ikpoba River in Benin city.