Essay: Heavy metals pollution in coastal sediments – Lagos port area

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  • Heavy metals pollution in coastal sediments - Lagos port area
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The objective of this study was to assess the heavy metals pollution in coastal sediments within the Lagos port area, Southwest Nigeria. This was with a view to investigate the heavy metal pollution and identify possible sources of pollutants.
Sediments samples were collected within the Lagos port area of Apapa, Tin Can Island and Ikorodu port complexes, with the aid of an anchored engine boat and a Van Veen grab sampler. These samples were put into closed polythene bags to avoid cross contamination, after which they were transported to the laboratory, and air dried for two weeks under controlled environment. Thereafter, samples were pulverized, weighed (300 mg) and pelletized. Elemental analyses were carried out using proton induced x-ray emission (PIXE) spectrometry. The PIXE experiment was performed using a 2.5 MeV proton beam obtained from the Center for Energy Research and Development (CERD) ion bean analysis (IBA) facility. The data obtained were interpreted using statistical tools such as Enrichment factor (EF), Pollution load index (PLI), Pearson correlation matrix and Principal component factor analysis (PCFA).
Seven heavy metals: Ti, Cr, Mn, Fe, Zn, V and Ce were detected and their concentrations were determined. The concentrations of the Ti (7159.60 ppm), Cr (607.97 ppm), Mn (1218.31 ppm), Fe (63278.44 ppm), Zn (399.14 ppm), Ce (1063.40 ppm) and V (204.85 ppm) were high. The heavy metals were present in all samples except for vanadium and cerium. The heavy metals vary significantly within samples and between sites. The heavy metals were found to exceed their background levels at most site of the study area, with the Cr and Zn levels found to be comparably more enriched. This was corroborated by the elevated Enrichment factor (EF) and Pollution load index (PLI) values for the heavy metals suggesting significant anthropogenic contributions with little of bedrock/crustal materials contributions to the samples obtained from the study area. Principal component analysis (PCFA) indicated two groups (Ti, Cr, Fe and Mn) and (Zn and Cr) that showed high inter-elemental relationship between them as a consequence of their highly significant positive correlations. This was corroborated by Pearson correlation matrices (PCM) for the analyzed elements. The PCFA and the PCM results confirmed that the high positively correlated elements had similar sources. From the PCFA result, the first group which comprises Ti, Cr, Fe and Mn indicated contamination via similar sources such as industrial effluent and sewages with little of bedrock/crustal materials contributions. The second group comprised Zn and Cr which indicated the dual sources of the Cr from the study area and suggested other contamination sources such as municipal and domestic sewages, urban runoff, port activities such as ship painting and repairs, loading and unloading of vessels, and discharges from passerby ship/boats such as oil, bilge and garbage.
This study concluded that the sediment samples of the Apapa, Tin Can Island and Ikorodu port complexes were polluted with the heavy metals. The sources of these metals were anthropogenic with little of bedrock/crustal materials contributions.
Keywords: Heavy metal; Assessment; Coastal Sediments; Enrichment; Statistical
analysis; Nigeria.
1.0. Introduction
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.
2.0. Materials and Methods
2.1. Study Area
The Lagos port complex which comprises of the Apapa, Tin Can Island and Ikorodu port complexes are located on the Lagos lagoon and the Badagary creek. The Apapa and Tin can Island port complexes are located at the Badagary creek, west axis of the Lagos Lagoon via the Lagos harbor. Ikorodu port complex is located at the north axis of the Lagos Lagoon. The areas north and west of the lagoon are not well provided with good road network so many communities within; traditionally rely on water as means of transportation. These areas are selected because of their high commercial, industrial and to some extent domestic activities taking place there on a daily basis. The commercial and industrial activities accounts for 50% of ship traffic into the Nigerian ports excluding tankers, estimated to be approximately 3,500 vessels per annum. All the vessels calling at these ports carry enormous amount of waste including bilge, sludge, garbage, sewage, chemical waste (toxic and non-toxic) and in the absence of Reception Facilities all the ship generated waste are discharged into the sea within the vicinity of the ports. Table 2.1 shows the site descriptions with the Global Positioning Satellite locations (GPS) for samples collected from the Apapa, Ikorodu and Tin Can Island port complexes. Sites 1, 2, 15 & 16 are located near ports, sites 9, 8 & 10 near a port with an industrial complex sited in it. Sites 3, 4, 13, & 14 are located near residential areas/coastal communities. Sites 5, 6, 17 & 18 are located near industrial factories, sites 7, 11 & 12 near areas of no known anthropogenic activities.
2.2. Sampling
Sampling was conducted in the month of July, 2012, about the peak of rainy season. A total of eighteen samples were collected from the three locations (Apapa, Ikorodu and Tin Can Island port complexes). In each location, a total of six samples were collected as shown in figure 1.0. Samples were collected with the aid of an engine boat to assess the sites and a Van Veen grab sampler. The grab in an open condition tied to a rope was lowered in water by standing at the edge of the anchored boat, and when it reaches the seafloor, the rope was buzzed whereby the hook was released closing the grab halves and thereby trapping the sediment within the grab. The grab was carefully retrieved on board the vessel and contents were transferred to a clean plastic tub. The sediments were sub sampled into well labeled polythene bags. After each grab, the sampler, plastic tub and hand gloves were thoroughly washed to avoid cross contamination of the samples. Finally, the samples in the labeled polythene bags were placed in a plastic bucket and transported to the laboratory.

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