ABSTRACT

Surface sediments were obtained from Qua Iboe River, Ibeno, Nigeria were analyzed for levels of trace metals (Cd, Cu, Ni, Fe and Pb). sediment samples were collected at Akporecord, Asanganyin, Iwuochang and Okpuru. Control samples were also collected at Atasi stream also in Ibeno for study. Trace metals were analysed using wet digestion and the samples were treated using standard analytical techniques and metal levels were determined spectrophotometrically using Unicam 939/959 Atomic Adsorption Spectrophotometer. The results obtained showed the following mean concentration fro trace metal levels (mgkg-1): (88.63+11) Fe; (36.65 + 7.21); (19.34 + 1.90)Cu, (23.63 + 2.73)Ni; (8.80+ 1.23)Cd. The results revealed that the metals decreased in the order; Fe>Pb>Ni>Cu>Cd. Copper (Cu) and lead (Pb) values were within the permissible limits for uppolluted sediments as given by FEPA (1991) and WHO (2003). White Cd, Ni and Fe exceeded the acceptable levels recommended. The degree of contamination (Cdeg). Showed that bottom sediments studied were moderately contaminated while results obtained from enrichment factor analysis that lead (Pb) and Cadmium (cd) were from anthropogenic source. However, Nickel (Ni), copper (Cu) and iron (Fe) in sediment studied are based on natural processes.

CHAPTER ONE

1.0     INTRODUCTION

Sediment is the loose sand, clay, silt and other soil particles that is deposited at the bottom of body of waste or accumulated at other depositional sites, sediments can emanate from the erosion of bedrocks and soil or from the decomposition of plants and animals (Taylor et al., 2009).

          Mucha et al; (2003) opines that sediments are the ultimate sink of contaminants in the aquatic system. Information glean from the study of sediment provides a better view on the impact of distinct human activity on the other ecosystem. Sediment load and composition is highly reflective of the type and intensity of agricultural land used which is lead in determining the health and survival of aquatic organisms. It’s composition provides best natural archives of recent environmental changes.

          According to Martins et al. (1997) sediments besides being a habitat, it is also a major source of nutrient for aquatic organisms, hence an assessment of the concentration of metal contaminants and extent to which these metals has pollute the sediments is imperative.

          Multi-elemental analysis of sediments may reveal the presence of heavy metals which are contaminants and may have toxic influence on ground water and surface water and also on plants, animals and humans (Suciv et al. 2008). Accumulation of trace metals occur in upper sediment in aquatic environment by biological and geochemical mechanisms may become toxic to sediment-dwelling organisms and fish, resulting in death, reduce growth, or impaired reproduction and lower species diversity (Praleena et al., 2007). These elements also occur naturally in rocks forming minerals and ore minerals; here they can reach the environment from natural processes (Akinmosin et al., 2009).

          Heavy metals may accumulates to a toxic level in sediments without visible signs. This occur from normal geological phenomenon such as ore formation, weathering of rocks and leaching or due to increased population, urbanization, industrial activities agricultural practices, exploration and exploitation of natural resources (Ajayi and Osibanjo, 1981).

          Sediment analysis is vital to assessing qualities of total ecosystem of water body in addition to water sample analysis practiced for many years, because it reflects the long term quality situation independent of the current imputs (Adeyamo et al., 2008). Because sediments are also an important biological habitat, uptake of toxicants into the food web are influenced by toxicant concentration in sediments. Toxicant concentration and sediment toxicity may be analyzed, but these analysis fail to account for the influence that contaminated sediments has on the overlying water column of effect toxicant mixtures in the sediments has on benthic organisms.

1.1     TOXIC METALS

Toxic metals comprise a group of minerals that have no function in the body and in fact are very harmful to plant, animal and human beings. This is due to their industrial use for the past 300 years. The burning of fossil fuels without scrubbers and improper incineration of waste materials worldwide. Toxic metals are now everywhere on planet earth.

          Toxic metals effect on biochemical reaction in soils and sediments may vary with pH, organic matter content, particle size distribution, vegetation and total hydrocarbon content (Esser et al., 1991) worldwide increasing level of industrialization and urbanization has lead to environmental pollution (Filazi et al., 2003). With the rapid industria-lization and economic development, toxic metals are continuing to be introduced to soils and sediments via several pathways including fertilization, irrigation, rivers, runoff atmospheric deposition, and point sources where metals are produced as a result of mining, refining and refinishing by product.