Assessment of heavy metals contamination and sediment quality in Ondo coastal marine area, Nigeria

Abstract

Heavy metals contamination and sediment quality are parts of the major concerns of the aquatic ecosystem globally. To assess the contamination and sediment quality of the Ondo coastal marine area, a total of seventy two (72) sediment samples were collected from three sampling locations along the coastal region. The concentrations of As, Cd, Cr, Cu, Fe, Ni, Pb and Zn were determined by employing Atomic Absorption Spectrophotometry (AAS). The contamination status and quality were assessed by employing sediment enrichment factor (Ksef), contamination factor (Cfi), and modified degree of contamination (mCd), sediment quality guidelines (SQG), sediment toxicity degree (STd) and toxicity load index (TLI). The sources of heavy metals were defined by employing principal component factor analysis (PCFA) approach. Iron had the highest average concentration values of 417.50 ± 89.87, 369.38 ± 80.04 and 286.17 ± 65.21 μg/g at Ayetoro, Abereke and Awoye sites, respectively. The Ksef values of As, Zn, Pb and Cd were < 50 revealing severe enrichment. The Cfi values of As were >6 at Abereke and Awoye sites showing moderate contamination condition. The mCd value of Ayetoro site is 3.0 indicating moderate degree of contamination. The SQG-Q values for Abereke and Awoye were 2.5 and 3.5 representing potential of adverse effects on the biological organism in the sediments. The STd values for As, Cr, Cu, Zn, Ni and Pb were between 1 and 1.5 (1 < STd ≤ 1.5) indicating low toxic level. The result of TLI three sites was 0.52 implying low metals toxicity. PCFA analysis identified mixed source (anthropogenic and natural sources), transportation services, and wastes disposal activities as major sources of heavy metals in the sediment of the study area. This study indicated low contamination and toxicity level of sediment due to heavy metals but a progressive discharge and accumulation of heavy metals in the sediment could occur from continuous oil exploration, transportation services and wastes disposal activities which may threaten aquatic ecosystem.