Heavy Metal Contamination of Otofure Dumpsite Environment near Benin City Edo, Nigeria

This study characterized some indices of heavy metals in the soils of Otofure waste dumpsite environment near Benin City, Edo State in Southern Nigeria, in order to ascertain the level of heavy metal contamination of one of the several sites receiving municipal solid wastes daily. Six samples were collected at the dumpsite (DS) and the adjoining upland positions (US). The samples were air-dried, crushed and sieved through a 2mm sieve and pre-treated using standard methods before determining the heavy metal concentrations in Atomic Absorption Spectrophotometer (Bulk Scientific 210 VGP) according to the method of the Association of Analytical Chemists. Various pollution indexes were computed using the analytical data obtained. The computed Enrichment factor (EF) showed that Mn. Fe, and cu had no enrichment at the top and subsurface of the dumpsite. However, there was a significant Zn enrichment and enrichment with Ni and V at the topsoil; and Extreme enrichment with Cr, Cd, and lead of the soil at the dumpsite. Also, the soil Contamination factor (CF) indicated a moderate contamination of iron (Fe), manganese (Mn) and copper (Cu), Very High contamination of zinc (Zn), chromium (Cr), cadmium (Cd), lead (Pb), nickel (Ni) and vanadium (V). Pollution Load Index (PLI) showed that Otofure dumpsite is heavily polluted (PLI > 1) by heavy metals in general. Geoaccumulation Index (Igeo) showed that soils of Otofure dumpsite were unpolluted to moderately polluted for manganese (Mn) and copper (Cu), heavily polluted for zinc (Zn), Heavily to Extremely polluted for chromium (Cr), cadmium (Cd), lead (Pb), and nickel (Ni), and Extremely polluted for chromium (Cr), cadmium (Cd), lead (Pb) and vanadium (V). The potential ecological risk index (PERI) showed slight pollution for manganese (Mn), zinc (Zn) and copper (Cu), a very strong pollution for chromium (Cr), and an extremely strong pollution for lead (Pb), nickel (Ni) and cadmium (Cd). The risk index (RI) for Otofure dumpsite indicated a very strong risk or level D pollution for the higher elevation around the Otofure dumpsite environment that could pose human health risks if crops from that environment is ingested. This result thus suggest the need for a gradual shift from surface municipal waste dumping of solid wastes to well-engineered and managed recycling/sanitary landfill in Edo State and Nigeria in order to prevent heavy metal pollution of lands and possibly groundwater where shallow aquifers exist.