Heavy Metals Geochemistry and Pollution Status of Coastal Sediments in Ayetoro Area, Southwestern Nigeria

Abstract

Coastal sediments from Ayetoro, South-western Nigeria were systematically sampled and analysed for their heavy metals concentration. Fifteen costal sediment samples were taken using a Vanveen grab at sampling thickness and density of 10cm and 100 m respectively, while the depth of sampling was determined using single point Echo sounder. The heavy metals analysed were Cadmium (Cd), Lead (Pb), Copper (Cu), Nickel (Ni), Iron (Fe), Manganese (Mn) and Zinc (Zn) with Model 210 VGP Buck Scientific Atomic Absorption Spectrophotometer. The results showed that the respective locations are contaminated with metals from both geogenic and anthropogenic sources. SS15 (Eyin-more) is shown to be very strongly polluted with Cd and Pb whereas, PLI values of 1.06, 1.10 and 2,76 indicates that SS1, SS6 and SS16 have very high level of metal toxicity while other locations remain unpolluted. The average concentration of the heavy metals range from Fe with the highest concentration (15313.05 - 38399.11) mg/kg, followed by Pb (17.94-165.57) mg/kg; Zn (28.81-125.59) mg/kg; Cu (16.73-112.59) mg/kg, Cd (0.05-22.75) mg/kg and Ni (3.75-17.96) mg/kg with the lowest concentration. The average Enrichment Factor values showed that Cd and Pb has significant enrichment (7.67 and 5.71), followed by Cu, Ni, Zn having deficiency to minimal enrichment (1.31, 0.17, 1.02) whereas Cd and Pb is significantly enriched in all locations. This could be as a result of oil pollution from exploration and exploitation activities, improper waste disposal and industrial effluents which can result to brain damage, increasing the biological oxygen demand (BOD) of living organisms in the sea, destruction of the ecosystem and their food chain and web relationships, infant mortality as well as pollution of domestic and portable water sources. The dominance of Fe-Zn-Pb-Ni metal associations signified zinc ores or massive sulphide mineralization in the studied area. The coastal town of Ayetoro should be given more attention in terms of Environmental Safety Enforcement by the government.