Abstract

The coastal zone of Nigeria is a home to over 80% of the country’s industries, which have introduced significant levels of heavy metals into the marine environment. All the available literature shows that, this area of transgressive beach, of the Bight of Benin, Southwest, Nigeria, is among the poorly studied in term of heavy metal accumulation and distribution. Ten selected heavy metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) were investigated monthly from six locations for one annual cycle of 2016. Samples were subjected to digestion and Atomic Absorption Spectrophotometer to determine the concentrations of heavy metals. The results showed that all the heavy metals except for Cd did not pose any apparent risk to biota at all levels. The Contamination Factors (CF) of As, Cd and Mn, indicated a moderate contamination (1<CF<3). Degree of contamination (C_deg) ranged from 5.2 to 12.5 in both seasons. The PLI were less than one in all the sampling stations and seasons. The Enrichment Factor (EF) values for Cd and As obtained for all the locations ranged from 1.9 to 24.9 indicating a significant enrichment of Cd and As in sediment. The Index of Geoaccumulation (I_geo) of all the investigated metals were negative across the sampling stations except Cd, implying that there was low heavy metals contamination across the study area. The heavy metals in sediments of Ondo State coastal marine water might be derived from the mechanically weathered rock materials and anthropogenic activities.

Keywords: Rock; Bight of Benin; Anthropogenic; Geoaccumulation; Enrichment factor