Ballast water is important for safe and efficient operation of vessels, helping to maintain stability during voyage in seas and docking in harbours. However, ballast pose considerable environmental challenges because they are often laden with polluted sediments and invasive species. The Lagos Harbour, which houses in largest port in West Africa, receives about five thousand vessels annually which discharges ballast water and sediment into the water with the potential to cause environmental pollution. In the Nigerian context there is high potential for pollution due to weak regulations, poor enforcement and limited research of this kind in other to understand their composition, fate and impacts. This study aims at characterizing the chemical composition (Heavy metals- Arsenic, Cadmium, Chromium, Copper, Lead & Zinc, as well as carbon and nitrogen content) of the ballast sediment because of their positive correlation with the survival of invasive species in the ballast water and sediment tanks. A total of four ships (2 cargos and 2 tankers) were surveyed within Lagos Harbour and surface (1-5 cm) sediment samples were scooped using a specialized grab for sampling ballast sediments. The sediments were transferred in specialized cool boxes to the University of Portsmouth in United Kingdom for analysis. Total metal concentrations were analysed using X-ray fluorescence (XRF). They were subjected to two acid digestions: Aqua regia (AR) and 1 M hydrochloric acid (1 M HCl ) following the procedures set out by the Canadian National Water Research Institute (NWRI) and the United States Environment Protection Agency (US-EPA Method 3050B). Total carbon and nitrogen contents were determined using an in-line Yanaco MT-5 CHN analyser. The results obtained were compared with established guidelines and subjected to correlation and Principal Component Analysis (PCA). The findings indicated high concentrations of Arsenic, Lead, Cadmium, Carbon and Nitrogen in the sediments. Tanker vessels contained relatively higher concentrations of the pollutants than cargo vessels. The findings from this study provides interesting baseline data which will guide a more intensive investigation of chemical composition of ballast water and sediments for effective comparison with what is obtainable elsewhere in the world. The maritime industry needs to pay close attention to ballast management particularly in developing countries like Nigeria where there is limited regulation for management of coastal areas with respect to shipping activities as a potential source of marine pollution. The IMO needs to direct further effort at investigating the non-biological components of ballast water and sediments in other to protect valuable biodiversity.
Keywords: Coastal Pollution, Ballast Water Management, Chemical Composition, Lagos Harbour, Ships, Analytical Techniques