Coastal pollution is a change in the physical, chemical and biological characteristics of water and sediments. This causes degradation of the natural quality of the coastal environments, and affects the health and survival of all forms of life (National Institute of Oceanography Dona Paula, India, 2008). Coastal pollution has been found to be a major problem in developing countries and the trends are expected to increase. Water bodies such as oceans, seas, rivers, streams and so on, are often contaminated by the activities of man such as rapid urbanization, exponential increase in population and high level of industrialization to the extent that these water bodies and the aquatic lives therein have been threatened to a devastating point.
There are different sources of effluent discharged into water bodies which mainly include industrial sources, agricultural sources and domestic sources. Other sources include harbor channel dredging, shipping activities, offshore exploration and exploitation, infrastructural development, weathering of minerals/parent rocks, leaching of ore deposits, volcanism-extruded products and atmospheric depositions. This has entailed a tremendous increase in discharge of a wide diversity of pollutants to receiving water bodies and has caused undesirable effects on the different components of the aquatic environment and on fisheries (Saad et al., 1994; Marcovecchio et al., 2007).
Sediments are complex mixtures of a number of solid phases that may include clays, silica, organic matter, carbonates and large bacterial populations. Sediments comprise an important component of aquatic ecosystems, providing habitat for a wide range of benthic and epi-benthic organisms. Bottom sediments consist of particles that have been transported by water, air or glaciers from the sites of their origin in a terrestrial environment and have been deposited on the floor of a river, lake, or ocean (Pravin et al., 2011).
Several reviews have shown that sediments serve as a metal pool that can release metals to the overlying water via natural or anthropogenic processes, causing potential adverse health effects to the ecosystem (Fatoki and Mathabatha, 2001; Ololade et al., 2007a). Sediments accumulate contaminants and serve as sources of pollution to the ecosystems they are connected with. These include pathogens, metals, and organic chemicals which associate themselves with particulate matter and eventually settle in depositional areas. If the loading of these contaminants into the waterways is large enough, the sediments may accumulate excessive quantities of contaminants that directly and indirectly disrupt the ecosystem, causing significant contamination and loss of desirable species (Burton, 2001).
Among these metal contaminants, some of which are referred to as ‘heavy metals’ are widely used in scientific literatures and are defined as a generally collective term which applies to the group of metals or metalloids with an atomic density greater than 4 g/cm3(Duffus, 2002). Heavy metals, although a loosely defined term, are widely recognized and usually apply to the widespread contaminants of terrestrial and freshwater ecosystems. Examples of heavy metals are, Antimony (Sb), Arsenic (As), Bismuth (Bi), Cadmium (Cd), Cerium (Ce), Cobalt (Co), Chromium (Cr), Copper (Cu), gallium (Ga), Gold (Au), Iron (Fe), Nickel (Ni), Lead (Pb), Manganese (Mn), Molybdenum (Mo), Mercury (Hg), Silver (Ag), Tellurium (Te), Thallium (Tl), Uranium (U), Selenium (Se), Tin (Sn), Titanium (Ti), Tungsten (W), Vanadium (V), Zinc (Zn) and the platinum group metals, which comprises Platinum (Pt), Palladium, Rhodium, Ruthenium, Osmium, and Iridium. Unlike almost all organic pollutants, such as organochlorines, heavy metals are elements which occur naturally in the Earth’s crust. They are therefore found naturally in soils and rocks with a subsequent range of natural background concentrations in soils, sediments, waters and organisms. Anthropogenic releases can give rise to higher concentrations of the metals relative to the normal background values. Furthermore, Heavy metals are non-bio-degradable; therefore they will persist in the environment. Contrary to many organic pollutants which eventually degrade to carbon dioxide and water, heavy metals will tend to accumulate in the environment especially in lake, estuarine or marine sediments and can be transported from one environment compartment to another (Duffus, 2002).
Therefore, sediments analysis is important as it can be used to monitor heavy metals pollution in the aquatic ecosystem. Several studies have documented the importance of sediment contamination for ecosystem quality and the widespread incidence of sediment contamination (e.g. Burton 1992; USEPA, 1997). They are also considered an important indicator for environmental pollution; they act as permanent or temporary traps for materials spread into the environment (DeGregori et al., 1996).
From contamination perspective, we understand that sediments are extremely important to the food web and serve as a reservoir of contaminants for bioaccumulation and trophic transfer (Burton 1992). Additionally, pollutants released to surface water from industrial and municipal discharges, atmospheric deposition and run off from agricultural, urban and mining areas can accumulate to harmful levels in sediments (Chukwujindu et al., 2007). Sediment analysis allows contaminants that are adsorbed by particulate matter, which escape detection by water analysis, to be identified.
In Nigeria, the coastal area is about 800 km2 in length from Lagos in the West to Calabar in the east. The coastal belt has estuaries and lagoons as a transition zone between it and the numerous rivers and creeks flowing southwards into the Atlantic. Numerous settlements and some major cities e.g. Lagos, Port Harcourt, Warri and Calabar are located near the estuaries and lagoon. They have sea ports and a variety of industrial establishments producing different industrial waste and effluents. Industrial establishments in Lagos alone accounts for greater than 40% of all industries in Nigeria. The proliferation of urban settlements and slum in the city of Lagos has also meant increased human pressure and the generation of domestic effluents, which eventually find their way into the Lagos Lagoon. The lagoon receives a complex mixture of domestic and industrial waste and has served as the ultimate sink for the disposal of domestic sewage since the latter part of the 19th century. In recent years, a decline in a hitherto viable commercial artisanal fishery pointed to environmental degradation and possible changes in water quality with biological consequences for the biota in the environment.
This present study focuses on the assessment of the heavy metals pollution in coastal sediments within the Lagos port area, Southwest Nigeria. With an aim to assess the level of the heavy metal pollution and identify the possible sources of pollution. In this regards, statistical tools such as enrichment factor (EF), pollution load index (PLI), Pearson correlation matrix (PCM) and principal component factor analysis (PCFA) will be of immense benefits.
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