AbstractDue to the combination of its restricted water circulation, the rise in shipping intensity and industrial activities, the coastal zone of Lagos Harbour, Nigeria, is vulnerable to contamination with heavy metals. The purpose of this study was therefore to investigate and characterise the concentration of heavy metals in the sediments of Lagos Harbour applying a variety of improved and efficient metal extraction and determination methods.
A total of 26 sampling sites were established for sample collection within Lagos Harbour and Lagos Lagoon, while nearby Apese Lagoon was chosen as a control zone. Surface (1-5 cm) sediment samples were collected using a Van Veen grab on three occasions during the 2013 and 2014 dry seasons, and the 2013 wet season. Total metal concentrations were analysed using X-ray fluorescence (XRF). The sediments 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). The results from the metal analysis were computed into GIS for spatial distribution using WinGlink software followed by correlation analysis, Principal Component Analysis (PCA), Cluster analysis of similarities, contamination (Cf) and enrichment factors (Ef).
The significant elements studied in this research were As, Cd, Cr, Cu, Co, Fe, Pb, Mn, Ni, V and Zn. The total analysis (XRF) showed that Cu and Zn significantly exceeded the threshold effect level (TEL), while the Aqua regia analysis showed that recoverable As significantly exceeded the TEL across the three sites, and 1 M HCl, however, showed that all the bioavailable metals were below the TEL across all three sites.
The contamination factor (Cf) indicated that in the 2013 dry season bioavailable Ni had the highest contamination factor at a petroleum products tank farm in Lagos Harbour. In the 2013 wet season XRF showed that the sediments in both Lagos Harbour and Lagos Lagoon were contaminated with Cd and Zn, while Aqua regia analysis showed Cu contamination in the sediments from Lagos Lagoon. Results from the 2014 dry season showed a generally higher trend in Cf.
The enrichment factor of metals in the sediment was measured in the surficial sediments at the three sites in order to identify metals with significant enrichment from anthropogenic sources. Generally, Aqua regia analysis showed higher enrichment of metals and metalloids in the sediments in Lagos Harbour than in Lagos Lagoon.
The interrelationship of the metals and grain particle sizes showed (using XRF) that As, Cd, Cu, Mn were significantly loaded in the coarse sand and silt. Using Aqua regia, As, Cr, Cd were bioavailable in clay, silt and coarse sand. While 1 M HCl showed that Cr, Cu and Fe were distributed in clay, silt and coarse sand respectively. The factors scores plot showed clusters which indicated that metal concentrations were affected by type of anthropogenic activity, geographical proximity and sea water incursion, but diffused runoff entry during the wet season made the clusters rather weaker. The major identified metal pollution hotspots were the Atlas cove, petroleum tank farm areas and ports in the Lagos Harbour while in the Lagos Lagoon they ii include the entry canal points of municipal sewage and runoff, coastal solid waste dump and receiving waters for industrial effluents.
These findings are significant for the development of baseline data to inform the formulation of guidelines for the protection of marine environment within the Nigerian Harbour system. This is in line with the United Nation Sustainable Development Goals #14 and #17: ‘Conserve and sustainably use the ocean, seas and marine resources’ and ‘Strengthen the means of implementation and revitalize the global partnership for sustainable development’. Moreover, these data can be used by the Nigerian authorities to improve harbour life and marine biota, and by other researchers interested in constructing efficacious testing methods.
|Date of Award||Mar 2019|
|Supervisor||Mike Fowler (Supervisor) & Graham Mills (Supervisor)|