Geochemical evaluation of the Lagos lagoon sediments and water.

Abstract

The Lagos lagoon is a depository of last resort for over 70% of the surface runoffs, drainage channels and important rivers flowing from interior Nigeria to the Atlantic Ocean. The surrounding densely populated and industrialized areas often result in the introduction of potential harmful materials into the Lagoon. This work is aimed at providing reference data for the quality assessment of the Lagoon. One hundred sediment samples obtained from the Lagoon were air dried at room temperature, disaggregated, sieved and digested using aquaregia and subsequently analyzed with the ICP-OES for elemental composition. 30 water samples were also obtained and analyzed for their metal contents. The geochemical results showed that the order of abundance of the major oxides were Fe O >SO >Na O>Al O >CaO>MgO>K O>TiO . The concentration of the trace 2 3 4 2 2 3 2 2 elements in ppm showed the following pattern of distribution: Cd (Bdl-3.7); Cu (3.0-231); Mn (64.0-1737); Mo (Bdl-28); Ni (3-49); Pb (2.0-146); Zn (9-366); As (Bdl-28); B (Bdl-27); Ba (9-167); Be (Bdl-3); Bi (Bdl-8); Co (Bdl-23); Cr (6-87); Ga (Bdl-15); La (7-87); Sb (Bdl-11); Sc (.9-11); Sr (4-192); Te (Bdl-6); Th (Bdl-10); Tl (Bdl-15); V (4-124);W (Bdl-8); Y (2-27) and Zr (1-30). The metal content of the lagoon water also revealed the following metal concentration range in ppm: Fe (4.20-43.67); B (0.08-0.41); Ni (Bdl-0.16); Cu (Bdl-0.016); Zn (0.02-0.118) and Pb (0.01-0.08). The geochemical evaluation of the metals contents of the sediments and water revealed that the metal loads of the media surpass their natural background while Pb, Cd, Bi, Tl, W, Cu and Zn are metals that are of significant environmental implications.