A Study of Heavy Metals Pollution in the Coastal Marine Sediment of Ondo State, Nigeria

Abstract

The present study was carried out to assess the pollution status of heavy metals in the marine sediment in Ondo coastal area. A total of 36 sediment samples were collected from the three locations (Awoye, Abereke and Ayetoro) once in a month in 2015 covering both dry and wet season. The sediment samples were subjected to digestion and Atomic Absorption Spectrophotometer (AAS) was used to measure the concentrations of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn. The measured concentrations data were used for evaluating the contamination level and accumulation status of heavy metals in sediment by employing several pollution indices: contamination factor (CF), degree of contamination (Cdeg), pollution load index (PLI), enrichment factor (EF) and index of geoaccumulation (Igeo). The results showed that Fe had the highest average concentration values of 248.00§ 20.00 and 324.33§ 5.80 mg/kg at Awoye sampling site for wet and dry season, respectively while the highest mean concentration of Mn were 271.77±9.50 and 295±10.06 mg/kg at Abereke and Ayetoro, respectively. The contamination factor (CF) values for As, Cd and Mn were 1 < CF < 3, indicating a moderate contamination. The results of Cdeg were ranged from 8.6 to 12.5 for both dry and wet season except in Ayetoro site that had 7.8 in the wet season. The PLI values were 0.47, 0.50 and 0.54 (<1) for Abereke, Awoye and Ayetoro sites, respectively, denoting unpolluted conditions. The EF values for Pb and Ni obtained from all the sites ranged from 20.8 to 38.9, showing their significantly enriched in sediment. The Igeo values of As, Cr, Fe, V, Zn and Cu were less than one (Igeo <1) for the three sampling locations in both seasons, implying that the sediments in the study area are practically uncontaminated by these metals. Pb had the Igeo values of 2.80 and 2.85 during dry and wet season at Awoye sampling site while Ni had 2.57 at Abereke only in the dry season. The heavy metals in sediment might be derived from the upstream rivers from the top soil, mechanically weathered rock materials and anthropogenic activities.