Vertical Profiling and Contamination Risk Assessment of Some Trace Metals in Lagos Lagoon Axis

Abstract

Lagos Harbour (a Lagos lagoon axis) serves as a route for goods transportation, coupled with proliferation of urban and industrial establishments. The socioeconomic activities within has often led to the introduction of substantial wastes, marine debris and spills into the harbor. In an attempt to monitor the pollution status of aquatic organisms in the Lagos Lagoon axis, vertical profiling of the trace metal contents was carried out to reveal, the vertical variations in the monthly trends of; Cu, Zn, Pb, Cr, Mn, Ni, and Fe between August and October,2014.Chemical analysis was carried out in the Nigerian institute for oceanography and marine research (NIOMR) wet and instrumentation laboratory, using aqua regia digestion methods and 200AA series Atomic Absorption Spectrophotometer. The observed levels of the trace metals shows a decreasing order of abundance; Fe > Cr > Pb > Mn> Ni > Zn > Cu; Fe > Pb > Cr > Ni > Mn > Zn >Cu and Fe > Cr > Pb > Ni > Mn > Zn > Cu for 0.2meters, 2.6meters and 5.2meters respective depth profile. This study reveal a general contamination trends; medium depth (2.6m) > bottom depth (5.2m) > surface depth (0.2m). Higher metal concentrations were observed in October. All observed trace metals except Cu, Zn and Fe exhibit high contamination ratio. The trace metals distributions in the study area are majorly controlled by; precipitations, dilution, anthropogenic activities and Sea/fresh water incursion from the Atlantic Ocean and the adjourning creeks. A strong regulation in the indiscriminate waste dump and a check in the socioeconomic activities in the Lagos Harbour are very essential.