Assessment of Heavy Metal Enrichment and Level of Contamination of Floodplains Soil in Ondo State, Nigeria

Flooding is one significant process that contributes to the movement of sediment and metals. With higher velocities of water, flooding can take contamination downstream. The soil samples were collected from three floodplains of Owena river, Ogbese river and Ala river in Ondo State were analyzed for their physico-chemical characteristics. The study also investigated the chemical speciation of Cd, Cu, Ni and Zn and total concentration in the soil samples. The concentration of the heavy metals in the selected floodplains were orderly as Zn > Cu > Ni > Cd. Investigating the speciation showed that contribution to the total metal content of the alluvial soil was from both geogenic and anthropogenic sources. Pollution/Contamination index evaluation showed that the alluvial soils had very slight metal contamination for all the metals except for Cd being found in the range of very severe contamination to slight contamination in Owena and Ala floodplains. The enrichment factor of the heavy metals had a general trend of Ni = Cu < Zn < Cd. The geo-accumulation index also had a general trend of Ni < Cu < Zn < Cd. The pollution index had highest value in Ala.